McKnight's Physical Geography: A Landscape Appreciation [11 ed.] 9780321820433, 0321820436, 2012039478, 0321864042, 9780321864048 - EBIN.PUB (2022)

MCKNIGHT’S

Physical Geography A Landscape Appreciation

MCKNIGHT’S

ELEVENTH EDITION

Physical Geography A Landscape Appreciation DARREL HESS City College of San Francisco Illustrated by DENNIS TASA

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Library of Congress Cataloging-in-Publication Data Hess, Darrel. McKnight’s physical geography : a landscape appreciation / Darrel Hess ; illustrated by Dennis Tasa. — 11th ed. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-321-82043-3 (hardcover : alk. paper) ISBN-10: 0-321-82043-6 (hardcover : alk. paper) 1. Physical geography. I. McKnight, Tom L. (Tom Lee). 1928–2004 Physical geography. II. Title. III. Title: Physical geography. GB54.5.H47 2013 910’.02—dc23 2012039478

www.pearsonhighered.com

1 2 3 4 5 6 7 8 9 10—DOW—16 15 14 13 12 ISBN-10: 0-321-82043-6; ISBN-13: 978-0-321-82043-3 (Student Edition) ISBN-10: 0-321-86404-2; ISBN-13: 978-0-321-86404-8 (Instructor’s Review Copy)

BRIEF CONTENTS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Introduction to Earth 2 Portraying Earth 30 Introduction to the Atmosphere 54 Insolation and Temperature 76 Atmospheric Pressure and Wind 108 Atmospheric Moisture 140 Atmospheric Disturbances 176 Climate and Climate Change 206 The Hydrosphere 252 Cycles and Patterns in the Biosphere 280 Terrestrial Flora and Fauna 306 Soils 344 Introduction to Landform Study 374 The Internal Processes 400 Preliminaries to Erosion: Weathering and Mass Wasting 446 Fluvial Processes 466 Karst and Hydrothermal Processes 498 The Topography of Arid Lands 514 Glacial Modification of Terrain 540 Coastal Processes and Terrain 572

APPENDIX I

The International System of Units (SI) A-1

APPENDIX II U.S. Geological Survey Topographic Maps A-3 APPENDIX III Meteorological Tables A-8 APPENDIX IV The Weather Station Model A-13 APPENDIX V Köppen Climate Classification A-19 APPENDIX VI Biological Taxonomy A-21 APPENDIX VII The Soil Taxonomy A-23

v

GEOSCIENCE ANIMATION LIBRARY

Animation Convection and Plate Tectonics

Covering the most difficult-to-visualize topics in physical geography, the Geoscience Animations can be accessed by students with mobile devices through Quick Response Codes in the book, or through the Study Area. Teachers can assign these media with assessments in .

1

Introduction to Earth

14

Solar System Formation Earth-Sun Relations

2

Plate Boundaries Seafloor Spreading Paleomagnetism Convection and Plate Tectonics Divergent Boundaries Subduction Zones Collision of India with Eurasia Transform Faults and Boundaries Assembly and Breakup of Pangaea Mantle Plumes Terrane Formation Volcanoes Formation of Crater Lake The Eruption of Mount St. Helens Igneous Features Folding Faulting Seismic Waves Seismographs

Portraying Earth Map Projections

3

Introduction to the Atmosphere Ozone Depletion Coriolis Effect

4

Insolation and Temperature Atmospheric Energy Balance Ocean Circulation Patterns—Subtropical Gyres Global Warming

5

Atmospheric Pressure and Wind Development of Wind Patterns Cyclones and Anticyclones Global Atmospheric Circulation The Jet Stream and Rossby Waves Seasonal Pressure and Precipitation Patterns El Niño

6

Atmospheric Moisture Hydrologic Cycle Phase Changes of Water Adiabatic Processes and Atmospheric Stability Seasonal Pressure and Precipitation Patterns

7

Atmospheric Disturbances Cold Fronts Warm Fronts Midlatitude Cyclones Hurricanes Tornadoes

8

Climate and Climate Change Seasonal Pressure and Precipitation Patterns End of the Last Ice Age Orbital Variations and Climate Change

9

10

Cycles and Patterns in the Biosphere Net Primary Productivity Biological Productivity in Midlatitude Oceans

13 vi

15

Introduction to Landform Study Metamorphic Rock Foliation Isostasy

Preliminaries to Erosion: Weathering and Mass Wasting Mechanical Weathering Mass Wasting Eruption of Mount St. Helens

16

Fluvial Processes Stream Sediment Movement Oxbow Lake Formation Floods and Natural Levee Formation Stream Terrace Formation

18

The Topography of Arid Lands Wind Transportation of Sediment Desert Sand Dunes

19

Glacial Modification of Terrain End of the Last Ice Age Isostasy Flow of Ice within a Glacier Glacial Processes Orbital Variations and Climate Change

The Hydrosphere Hydrologic Cycle Tides Ocean Circulation Patterns—Subtropical Gyres Ocean Circulation Patterns—Global Conveyor-Belt Circulation The Water Table Groundwater Cone of Depression

The Internal Processes

20

Coastal Processes and Terrain Wave Motion and Wave Refraction Tsunami Tides Coastal Sediment Transport Movement of Barrier Island Coastal Stabilization Structures Seamounts & Coral Reefs

VIDEOS Video Hurricane Sandy

Videos providing engaging visualizations and real world examples of physical geography concepts can be accessed by students with mobile devices through Quick Response Codes in the book, or through the Study Area. Teachers can assign these media with assessments in .

2

Portraying Earth

8

Studying Fires Using Multiple Satellite Sensors

3

Introduction to the Atmosphere Ozone Hole Coriolis Effect Merry-Go-Round

4

Insolation and Temperature Seasonal Radiation Patterns Seasonal Changes in Temperature

5 6

Atmospheric Moisture Hydrologic Cycle Global Precipitation

7

20,000 years of Pine Pollen Temperature and Agriculture

9

Atmospheric Disturbances

The Hydrosphere Hydrologic Cycle

10

Cycles and Patterns in the Biosphere Global Carbon Uptake by Plants

11

Atmospheric Pressure and Wind El Niño La Niña

Climate and Climate Change

Terrestrial Flora and Fauna Climate, Crops, and Bees

13

Introduction to Landform Study Black Smokers

20

Coastal Processes and Terrain Movement of Sand in Beach Compartment Summertime/Wintertime Beach Conditions

Hurricane Hot Tower 2005 Hurricane Season Hurricane Sandy

vii

CONTENTS

GEOSCIENCE ANIMATION LIBRARY vi GEOSCIENCE VIDEO LIBRARY vii PREFACExvii ABOUT OUR SUSTAINABILITY INITIATIVES xxii ABOUT THE AUTHORS xxiii BOOK AND MasteringGeography WALKTHROUGH xxiv

1

Introduction to Earth 2

Geography and Science3 Studying the World Geographically4 The Process of Science6 Numbers and Measurement Systems7 Environmental Spheres and Earth Systems7 Earth’s Environmental Spheres7 Earth Systems8 Earth and the Solar System10 The Solar System10 The Size and Shape of Earth11 The Geographic Grid—Latitude and Longitude13 Latitude14 Longitude15 Locating Points on the Geographic Grid17 Earth–Sun Relations and the Seasons17 Earth Movements18 The Annual March of the Seasons19 Seasonal Transitions22 Significance of Seasonal Patterns23 Telling Time24 Standard Time24 International Date Line25 Daylight-Saving Time26

viii

2

Portraying Earth 30

Maps and Globes31 Maps32 Map Scale33 Scale Types33 Large and Small Map Scales34 Map Projections and Properties35 Map Projections35 Map Properties35 Families of Map Projections36 Cylindrical Projections36 Planar Projections37 Conic Projections38 Pseudocylindrical Projections38 Conveying Information on Maps39 Map Essentials39 Isolines40 Portraying the Three-Dimensional Landscape42 GPS—The Global Positioning System42 Remote Sensing44 Aerial Photographs44 Visible Light and Infrared Sensing44 FOCUS ▶ Using Remote Sensing Images to Study a Landscape45 Thermal Infrared Sensing46 Multispectral Remote Sensing46 Geographic Information Systems (GIS)49 Tools of the Geographer50

3

Introduction to the Atmosphere 54

Size and Composition of the Atmosphere55 Size of Earth’s Atmosphere56 Development of Earth’s Modern Atmosphere56 Composition of the Modern Atmosphere57 Permanent Gases57 Variable Gases57 Particulates (Aerosols)58

Contentsix

Vertical Structure of the Atmosphere59 Thermal Layers59 Pressure60 Composition61

Land and Water Temperature Contrasts94 Warming of Land and Water94 Cooling of Land and Water95 Implications95

Human-Induced Atmospheric Change62 Depletion of the Ozone Layer62 Air Pollution64 PEOPLE AND THE ENVIRONMENT ▶ The UV Index65 Energy Production and the Environment67

Mechanisms of Global Energy Transfer95 Atmospheric Circulation96 Oceanic Circulation96

Weather and Climate67 ENERGY FOR THE 21ST CENTURY

▶ Our Continuing

Dependence on Fossil Fuels68

The Elements of Weather and Climate69 The Controls of Weather and Climate69 The Coriolis Effect71

4

Insolation and Temperature 76

The Impact of Temperature on the Landscape77 Energy, Heat, and Temperature78 Energy78 Temperature and Heat79 Measuring Temperature79 Solar Energy80 Electromagnetic Radiation80 ENERGY FOR THE 21ST CENTURY ▶ Solar Power81 Insolation83 Basic Warming and Cooling Processes in the Atmosphere83 Radiation83 Absorption83 Reflection84 Scattering84 Transmission85 Conduction86 Convection87 Advection87 Adiabatic Cooling and Warming87 Latent Heat88 Earth’s Solar Radiation Budget88 Long-Term Energy Balance88 Earth’s Energy Budget89 Variations in Insolation by Latitude and Season90 Latitudinal and Seasonal Differences90 FOCUS ▶ Monitoring Earth’s Radiation Budget91 Latitudinal Radiation Balance92

Vertical Temperature Patterns98 Environmental Lapse Rate98 Average Lapse Rate99 Temperature Inversions99 Global Temperature Patterns100 Prominent Controls of Temperature100 Seasonal Patterns101 Annual Temperature Range102 Measuring Earth’s Surface Temperature by Satellite103 Climate Change and “Global Warming”103 Temperature Change During Twentieth Century104 Increasing Greenhouse Gas Concentrations104 Intergovernmental Panel on Climate Change (IPCC)105

5

Atmospheric Pressure and Wind 108

The Impact of Pressure and Wind on the Landscape110 The Nature of Atmospheric Pressure110 Factors Influencing Atmospheric Pressure110 Mapping Pressure with Isobars112 The Nature of Wind112 Direction of Movement113 Wind Speed114 Cyclones and Anticyclones115 The General Circulation of the Atmosphere116 ENERGY FOR THE 21ST CENTURY ▶ Wind Power117 Idealized Circulation Patterns118 Seven Components of the General Circulation119 Subtropical Highs119 Trade Winds121 Intertropical Convergence Zone (ITCZ)122 The Westerlies122 Polar Highs124 Polar Easterlies125 Polar Front125 Vertical Patterns of the General Circulation125 Modifications of the General Circulation126 Seasonal Variations in Location126 Monsoons127

xContents

Localized Wind Systems129 Sea and Land Breezes129 Valley and Mountain Breezes129 Katabatic Winds130 Foehn and Chinook Winds131 Santa Ana Winds131 El Niño-Southern Oscillation131 Effects of El Niño131 Normal Pattern132 El Niño Pattern133 La Niña134 Causes of ENSO134 Teleconnections134 PEOPLE AND THE ENVIRONMENT ▶ Forecasting El Niño135

Other Multiyear Atmospheric and Oceanic Cycles136 Pacific Decadal Oscillation136 The North Atlantic Oscillation and the Arctic Oscillation136

6

Atmospheric Moisture 140

The Impact of Atmospheric Moisture on the Landscape142 The Nature of Water: Commonplace but Unique142 The Hydrologic Cycle142 The Water Molecule143 Important Properties of Water143 Phase Changes of Water145 Latent Heat145 Importance of Latent Heat in the Atmosphere146 Water Vapor and Evaporation147 Evaporation and Rates of Evaporation147 Evapotranspiration148 Measures of Humidity148 Actual Water Vapor Content148 Relative Humidity149 Related Humidity Concepts150 Condensation151 The Condensation Process151 Adiabatic Processes151 Dry and Saturated Adiabatic Rates151 Significance of Adiabatic Temperature Changes153 Clouds153 Classifying Clouds153 Fog156

Dew157 Clouds and Climate Change157 Atmospheric Stability157 Buoyancy157 The Stability of Air157 PEOPLE AND THE ENVIRONMENT ▶ Global Dimming158 Determining Atmospheric Stability160 Precipitation161 The Processes161 Forms of Precipitation162 Atmospheric Lifting and Precipitation164 Convective Lifting164 FOCUS ▶ GOES Weather Satellites165 Orographic Lifting166 Frontal Lifting166 Convergent Lifting167 Global Distribution of Precipitation167 Regions of High Annual Precipitation167 Regions of Low Annual Precipitation168 Seasonal Precipitation Patterns169 Precipitation Variability170 Acid Rain171 Sources of Acid Precipitation171

7

Atmospheric Disturbances 176

The Impact of Storms on the Landscape177 Air Masses178 Characteristics178 Origin178 Classification178 Movement and Modification178 North American Air Masses179 Fronts180 Cold Fronts180 Warm Fronts181 Stationary Fronts181 Occluded Fronts181 Air Masses, Fronts, and Major Atmospheric Disturbances182 Midlatitude Cyclones182 Characteristics182 Movements184 Life Cycle184 Weather Changes with the Passing of a Midlatitude Cyclone186

Contentsxi

FOCUS ▶ Conveyor Belt Model of Midlatitude Cyclones187 Occurrence and Distribution188 Midlatitude Anticyclones188 Characteristics188 Relationships of Cyclones and Anticyclones188 Easterly Waves189 Characteristics189 Origin189 Tropical Cyclones: Hurricanes190 Categories of Tropical Disturbances190 Characteristics190 Origin192 Movement192 Damage and Destruction193 Hurricanes and Climate Change194 PEOPLE AND THE ENVIRONMENT ▶ Lessons of Hurricane Katrina195

Localized Severe Weather197 Thunderstorms197 Tornadoes199 PEOPLE AND THE ENVIRONMENT ▶ The Devastating Tornadoes of 2011201

Waterspouts202 Severe Storm Watches and Warnings202 FOCUS ▶ Wather Radar203

8

Climate and Climate Change 206

Subarctic Climate (Dfc, Dfd, Dwc, Dwd)228 Polar and Highland Climates (Groups E and H)230 Tundra Climate (ET)231 FOCUS ▶ Signs of Climate Change in the Arctic232 Ice Cap Climate (EF)233 Highland Climate (Group H)234 Global Patterns Idealized236 Global Climate Change237 Determining Climates of the Past237 Dendrochronology238 Oxygen Isotope Analysis238 Ice Cores239 Pollen Analysis240 Urban Heat Islands241 Causes of Long-Term Climate Change241 Atmospheric Aerosols241 Fluctuations in Solar Output242 Variations in Earth–Sun Relations242 Greenhouse Gases Concentration243 Feedback Mechanisms243 The Roles of the Ocean244 Anthropogenic Climate Change244 Evidence of Current Climate Change244 Natural or Anthropogenic Climate Change?246 Using Models to Predict Future Climate246 Projections of Future Climate247 Addressing Climate Change248 Mitigating and Adapting248 ENERGY FOR THE 21ST CENTURY ▶ Strategies for Reducing Greenhouse Gas Emissions249

Climate Classification208 Early Classification Schemes208 The Köppen Climate Classification System208 Climographs209 World Distribution of Major Climate Types210 Tropical Humid Climates (Group A)211 Tropical Wet Climate (AF)212 Tropical Savanna Climate (Aw)213 Tropical Monsoon Climate (Am)214 Dry Climates (Group B)216 Subtropical Desert Climate (BWh)217 Midlatitude Desert Climate (BWk)220 Mild Midlatitude Climates (Group C)221 Mediterranean Climate (Csa, Csb)222 Humid Subtropical Climate (Cfa, Cwa, Cwb)223 Marine West Coast Climate (Cfb, Cfc)224 Severe Midlatitude Climates (Group D)225 Humid Continental Climate (Dfa, Dfb, Dwa, Dwb)226

9

The Hydrosphere 252

The Hydrologic Cycle253 Surface-to-Air Water Movement254 Air-to-Surface Water Movement255 Movement On and Beneath Earth’s Surface255 Residence Times255 Energy Transfer in the Hydrologic Cycle256 The Oceans256 How Many Oceans?256 Characteristics of Ocean Waters257 Movement of Ocean Waters258 Tides259 Ocean Currents260 Waves261

xiiContents

PEOPLE AND THE ENVIRONMENT ▶ The Great Pacific Garbage Patch262

Permanent Ice—The Cryosphere263 Permafrost265 Surface Waters267 Lakes267 Wetlands268 Rivers and Streams270 Groundwater271 Movement and Storage of Underground Water271 Zone of Aeration272 Zone of Saturation273 Zone of Confined Water274 Waterless Zone275 Groundwater Mining275 FOCUS ▶ Monitoring Groundwater Resources from Space276

10

Cycles and Patterns in the Biosphere 280

The Impact of Plants and Animals on the Landscape281 The Geographic Approach to the Study of Organisms282 Biogeography282 The Search for a Meaningful Classification Scheme283 Biogeochemical Cycles283 The Flow of Energy284 ENERGY FOR THE 21ST CENTURY ▶ Biofuels286 The Hydrologic Cycle287 The Carbon Cycle287 The Oxygen Cycle288 The Nitrogen Cycle289 Mineral Cycles291 Food Chains291 Food Pyramids292 Pollutants in the Food Chain293 Biological Factors and Natural Distributions293 Evolutionary Development293 PEOPLE AND THE ENVIRONMENT ▶ The 2010 Deepwater Horizon Oil Spill294

Migration and Dispersal296 Reproductive Success296 Population Die-off and Extinction296 Plant Succession297 Environmental Factors299 The Influence of Climate299

FOCUS ▶ Bark Beetle Killing Forests in Western North America300 Edaphic Influences301 Topographic Influences301 Wildfire301 Environmental Correlations: The Example of Selva302

11

Terrestrial Flora and Fauna 306

Ecosystems and Biomes307 Ecosystem: A Concept for All Scales307 Biome: A Scale for All Biogeographers308 Terrestrial Flora308 Characteristics of Plants309 Floristic Terminology309 Environmental Adaptations310 Competition and the Inevitability of Change311 Spatial Associations of Plants312 Vertical Zonation313 Local Variations313 Terrestrial Fauna315 Characteristics of Animals316 Kinds of Animals316 Environmental Adaptations317 FOCUS ▶ Changing Climate Affects Bird Populations319 Competition among Animals321 Cooperation among Animals321 Zoogeographic Regions322 The Major Biomes324 Tropical Rainforest325 Tropical Deciduous Forest326 Tropical Scrub327 Tropical Savanna327 Desert329 Mediterranean Woodland and Shrub330 Midlatitude Grassland330 Midlatitude Deciduous Forest332 Boreal Forest332 Tundra334 Human Modification of Natural Distribution Patterns334 Physical Removal of Organisms335 Habitat Modification335 PEOPLE AND THE ENVIRONMENT ▶ Rainforest Loss in Brazil338

Introduction of Exotic Species339

Contentsxiii

12

Soils344

Soil and Regolith345 From Regolith to Soil346 Soil as a Component of the Landscape346 Soil-Forming Factors347 The Geologic Factor347 The Climatic Factor347 The Topographic Factor347 The Biological Factor348 The Time Factor350 Soil Components350 Inorganic Materials350 Organic Matter350 Soil Air351 Soil Water352 Soil Properties353 Color353 Texture354 Structure355 Soil Chemistry356 Colloids356 Cation Exchange356 Acidity/Alkalinity356 Soil Profiles357 Soil Horizons357 Pedogenic Regimes358 Laterization359 Podzolization359 Gleization360 Calcification360 Salinization360 Climate and Pedogenic Regimes361 Soil Classification361 The Soil Taxonomy361 The Mapping Question362 Global Distribution of Major Soils363 Entisols (Very Little Profile Development)363 FOCUS ▶ Using Soil Properties to Decipher Past Environmental Changes364

Inceptisols (Few Diagnostic Features)365 Andisols (Volcanic Ash Soils)365 Gelisols (Cold Soils with Permafrost)365 Histosols (Organic Soils on Very Wet Sites)366 Aridisols (Soils of Dry Climates)366 Vertisols (Swelling and Cracking Clays)367

Mollisols (Dark, Soft Soils of Grasslands)368 Alfisols (Clay-Rich B Horizons, High Base Status)369 Ultisols (Clay-Rich B Horizons, Low Base Status)370 Spodosols (Soils of Cool, Forested Zones)370 Oxisols (Highly Weathered and Leached)371 Distribution of Soils in the United States372

13

Introduction to Landform Study374

The Structure of Earth375 Earth’s Hot Interior376 The Crust376 The Mantle376 The Inner and Outer Cores377 Plate Tectonics and the Structure of Earth377 The Composition of Earth377 Minerals378 Rocks379 Igneous Rocks380 Sedimentary Rocks383 Metamorphic Rocks386 ENERGY FOR THE 21ST CENTURY ▶ Fracking for Natural Gas387

The Rock Cycle389 Continental and Ocean Floor Rocks390 Isostasy390 The Study of Landforms391 Some Critical Concepts392 Internal and External Geomorphic Processes392 Uniformitarianism393 Geologic Time393 Scale and Pattern395 An Example of Scale395 Pattern and Process in Geomorphology397

14

The Internal Processes400

The Impact of Internal Processes on the Landscape401 From Rigid Earth to Plate Tectonics402 Wegener’s Continental Drift402

xivContents

The Theory of Plate Tectonics404 The Evidence404 Seafloor Spreading404 Plate Tectonic Theory406 Plate Boundaries408 Divergent Boundaries408 Convergent Boundaries409 Transform Boundaries413 Plate Boundaries Over Geologic Time413 The Pacific Ring of Fire414 Additions to Plate Tectonic Theory415 Hot Spots and Mantle Plumes415 Accreted Terranes417 Remaining Questions417 Volcanism418 Volcano Distribution418 Magma Chemistry and Styles of Eruption419 Lava Flows421 Volcanic Peaks422 Volcanic Hazards426 Volcanic Gases426 Lava Flows427 Eruption Column and Ash Fall427 Pyroclastic Flows427 Volcanic Mudflows (Lahars)428 Monitoring Volcanoes429 Intrusive Igneous Features430 Plutons430 Folding432 The Process of Folding433 Types of Folds433 Topographic Features Associated with Folding433 Faulting434 Types of Faults435 PEOPLE AND THE ENVIRONMENT ▶ The 2010 Haiti Earthquake436

Landforms Associated with Normal Faulting437 Landforms Associated with Strike-Slip Faulting438

15

Preliminaries to Erosion: Weathering and Mass Wasting 446

Denudation447 The Impact of Weathering and Mass Wasting on the Landscape447 Weathering and Rock Openings448 Types of Rock Openings449 The Importance of Jointing449 Weathering Agents450 Mechanical Weathering450 Chemical Weathering454 Biological Weathering455 Differential Weathering455 Climate and Weathering456 Mass Wasting456 Factors Influencing Mass Wasting456 Fall458 Slide459 Flow460 Creep461 PEOPLE AND THE ENVIRONMENT ▶ The La Conchita Landslides462

16

Fluvial Processes 466

The Impact of Fluvial Processes on the Landscape467 Streams and Stream Systems468 Streamflow and Overland Flow468 Valleys and Interfluves468 Drainage Basins469 Stream Orders469 ENERGY FOR THE 21ST CENTURY ▶ Hydropower470

Earthquakes438 Seismic Waves438 Earthquake Magnitude439 Shaking Intensity439 Earthquake Hazards440

Fluvial Erosion and Deposition471 Erosion by Overland Flow471 Erosion by Streamflow471 Transportation472 Deposition473 Perennial and Intermittent Streams473 Floods as Agents of Erosion and Deposition473

Complexities of the Internal Processes—Example of the Northern Rockies441 FOCUS ▶ Earthquake Prediction442

Stream Channels474 Channel Flow475 Stream Channel Patterns475

Contentsxv

Structural Relationships477 Consequent and Subsequent Streams477 Stream Drainage Patterns477 The Shaping and Reshaping of Valleys480 Valley Deepening480 Valley Widening482 Valley Lengthening483 Deposition in Valleys486 Floodplains486 Floodplain Landforms487 Modifying Rivers for Flood Control489 Flood Control on the Mississippi River489 PEOPLE AND THE ENVIRONMENT ▶ The Changing Mississippi River Delta491

Stream Rejuvenation492 Theories of Landform Development493 Davis’s Geomorphic Cycle493 Penck’s Theory of Crustal Change and Slope Development494 Equilibrium Theory494

17

Karst and Hydrothermal Processes 498

The Impact of Solution Processes on the Landscape499

Fluvial Erosion in Arid Lands519 Fluvial Deposition in Arid Lands521 Climate Change and Deserts522 The Work of the Wind522 Aeolian Erosion523 PEOPLE AND THE ENVIRONMENT ▶ Desertification524 Aeolian Transportation525 Aeolian Deposition525 Aeolian Processes in Nondesert Regions528 Characteristic Desert Landscape Surfaces529 Common Desert Surfaces529 Erg—A Sea of Sand529 Reg—Stony Deserts529 Hamada—Barren Bedrock530 Two Representative Desert Landform Assemblages530 Basin-and-Range Landforms530 The Ranges531 The Piedmont Zone531 The Basins532 Death Valley: A Remarkable Example of Basin-and-Range Terrain532 Mesa-and-Scarp Terrain534 Structure of Mesa-and-Scarp Landforms534 Erosion of Escarpment Edge535 Arches and Natural Bridges535 Badlands536

Solution and Precipitation499 Caverns and Related Features501 Speleothems501 Karst Topography502 Karst Landforms502 Hydrothermal Features505 Hot Springs505 Geysers506 Fumaroles508 Hydrothermal Features in Yellowstone508 ENERGY FOR THE 21ST CENTURY ▶ Geothermal Energy509

18

The Topography of Arid Lands 514

A Specialized Environment515 Special Conditions in Deserts515 Running Water in Waterless Regions517 Surface Water in the Desert517

19

Glacial Modification of Terrain 540

The Impact of Glaciers on the Landscape542 Types of Glaciers542 Mountain Glaciers542 Continental Ice Sheets542 Glaciations Past and Present543 Pleistocene Glaciation544 Indirect Effects of Pleistocene Glaciations544 Contemporary Glaciation546 Glacier Formation and Movement548 Changing Snow to Ice548 Glacier Movement549 PEOPLE AND THE ENVIRONMENT ▶ Disintegration of Antarctic Ice Shelves550

Glacier Flow versus Glacier Advance551

xviContents

The Effects of Glaciers551 Erosion by Glaciers551 Transportation by Glaciers552 Deposition by Glaciers552 Continental Ice Sheets554 Development and Flow554 Erosion by Ice Sheets554 Deposition by Ice Sheets556 Glaciofluvial Features558 FOCUS ▶ Shrinking Glaciers560 Mountain Glaciers561 Development and Flow of Mountain Glaciers561 Erosion by Mountain Glaciers561 Deposition by Mountain Glaciers565 The Periglacial Environment566 Patterned Ground567 Proglacial Lakes567 Causes of the Pleistocene Glaciations568 Climate Factors and the Pleistocene569 Are We Still in an Ice Age?569

20

Coastal Processes and Terrain 572

PEOPLE AND THE ENVIRONMENT ▶ The 2011 Japan Earthquake and Tsunami580

ENERGY FOR THE 21ST CENTURY ▶ Tidal Power582 Ice Push583 Organic Secretions583 Stream Outflow583 Coastal Sediment Transport583 Coastal Depositional Landforms585 Sediment Budget of Depositional Landforms585 Beaches585 Spits586 Barrier Islands586 Human Alteration of Coastal Sediment Budgets588 Shorelines of Submergence and Emergence590 Coastal Submergence590 Coastal Emergence591 Coral Reef Coasts592 Coral Polyps592 Coral Reefs593 FOCUS ▶ Imperiled Coral Reefs594

LEARNING CHECK ANSWERSAK-1 APPENDIX I The International System of Units (SI) A-1

APPENDIX II U.S. Geological Survey Topographic Maps A-3 The Impact of Waves and Currents on the Landscape573 Coastal Processes574 The Role of Wind in Coastal Processes574 Coastlines of Oceans and Lakes574 Waves575 Wave Motion575 Wave Refraction576 Tsunami578 Important Shoreline-Shaping Processes579 Tides579 Changes in Sea Level and Lake Level579

APPENDIX III Meteorological Tables A-8 APPENDIX IV The Weather Station Model A-13 APPENDIX V Köppen Climate Classification A-19 APPENDIX VI Biological Taxonomy A-21 APPENDIX VII The Soil Taxonomy A-23 GLOSSARY G-1 PHOTO C-1 ILLUSTRATION AND TEXT CREDITS C-3 INDEX I-1

PREFACE

McKnight’s Physical Geography: A Landscape Appreciation presents the concepts of physical geography in a clear, readable way to help students comprehend Earth’s physical landscape. The 11th edition of the book has undergone a thorough revision, while maintaining the time-proven approach to physical geography first presented by Tom McKnight nearly 30 years ago.

NEW TO THE 11TH EDITION Users of earlier editions will see that the overall sequence of chapters and topics remains the same, with material added or updated in several key areas. Changes to the new edition include the following: t 5IFFOUJSF BSUQSPHSBN IBTDPOUJOVFE JUTUIPSPVHI revision and updating by illustrator Dennis Tasa. Dozens of new diagrams, maps, and photographs are found throughout. t &BDIDIBQUFSJODMVEFTBOFXMFBSOJOHQBUI CFHJOOJOH with a series of new Key Questions to help students prioritize key issues and concepts. t $IBQUFSTOPXPQFOXJUIOFXSeeing Geographically features that ask students observational questions about the chapter’s opening image, and are revisited in the end-of-chapter Learning Review. t 5ISPVHIPVUFBDIDIBQUFS OFXLearning Check questions periodically confirm a student’s understanding of the material. t "O FYQBOEFE FOEPGDIBQUFS Learning Review now includes new basic quantitative Exercises. t 5IFTFSJFTPGCPYFEFTTBZTDBMMFEEnergy for the 21st Century has been expanded from the 10th edition (where it was called Renewable Energy). The boxes have been updated and are now more closely tied to the main text. Contributed by professors from across the country, the essay topics include Our Continuing Dependence on Fossil Fuels; Solar Energy; Wind Energy; Strategies for Reducing Greenhouse Gas Emissions; Fracking for Natural Gas; Geothermal Energy; Biofuels; Hydropower; and Tidal Power. t *O$IBQUFS JOGPSNBUJPOPOEarth’s Environmental Spheres and Earth Systems has been greatly expanded. t *O$IBQUFS NBUFSJBMPOcontour lines and portraying the three-dimensional landscape has been reorganized. t .BUFSJBM PO UIF development of Earth’s modern atmosphere has been added to Chapter 3. t *O $IBQUFS UIF TFDUJPO PO UIF Coriolis effect has been revised and reorganized to clarify the concept for students, and examples have been added of topics in later chapters for which understanding of the Coriolis effect is important.

t *O $IBQUFS UIF NBUFSJBM PO energy, heat, and temperature has been revised and expanded. t /FXEJBHSBNTJO$IBQUFSJMMVTUSBUFUIFPacific Decadal Oscillation. t $IBQUFS Climate and Climate Change, has been thoroughly updated and revised with the latest data and applications, and more detailed explanations of oxygen isotope analysis and radiocarbon dating. t 5IFNBUFSJBMPOrocks has been expanded in Chapter 13, as has the discussion of geologic time. t .BUFSJBMPOdifferential weathering is now incorporated into Chapter 15. t $IBQUFSPOdesert landscapes and Chapter 20 on coastal processes and landforms have been thoroughly reorganized for clarity. t 4PNFLFZNBUFSJBMQSFWJPVTMZGPVOE JO'PDVT#PYFTIBT been integrated directly into the text. Updated and revised Focus Boxes include The UV Index; Monitoring Earth’s Radiation Budget; Forecasting El Niño; GOES Weather Satellites; Global Dimming; Lessons of Hurricane Katrina; The Great Pacific Garbage Patch; Bark Beetles Killing Forests in Western North America; Signs of Climate Change in the Arctic; Climate Change Affects Bird Populations; Rainforest Loss in Brazil; The La Conchita Landslides; The Changing Mississippi River Delta; Disintegration of Antarctic Ice Shelves; Shrinking Glaciers; and Imperiled Coral Reefs. t /FX'PDVT#PYFTJODMVEFUsing Remote Sensing Images to Study a Landscape; The Conveyor Belt Model of Midlatitude Cyclones; Weather Radar; The Devastating Tornadoes of 2011; Monitoring Groundwater Resources from Space; The 2010 Deepwater Horizon Oil Spill; Using Soil Profiles to Decipher Past Environmental Changes; The 2010 Haiti Earthquake; Earthquake Prediction; Desertification; and The 2011 Japan Earthquake and Tsunami. t 2VJDL3FTQPOTF 23 $PEFTBSFJOUFHSBUFEUISPVHIPVU the book to enable students with mobile devices to access mobile-ready versions of the Geoscience Animations and new videos as they read, for just in time visualization and conceptual reinforcement. These media are also available in the Student Study Area of MasteringGeography, and many can also be assigned by teachers for credit and grading. t 5 I F U I F E J U J P O J T O P X T V Q Q P S U F E C Z MasteringGeography TM, the most widely used and effective online homework, tutorial, and assessment system for the sciences. Assignable media and activities include: Geoscience Animations, Videos, Encounter Physical Geography Google Earth™ Explorations, MapMaster™ interactive maps, coaching activities on the toughest topics in physical geography, end-of-chapter questions and exercises, reading quizzes, and Test Bank questions. xvii

xviiiPreface

TO THE STUDENT Welcome to McKnight’s Physical Geography: A Landscape Appreciation. Take a minute to skim through this book to see some of the features that will help you learn the material in your physical geography course: t :PVMMOPUJDFUIBUUIFbook includes many diagrams, maps, and photographs. Physical geography is a visual discipline, so studying the figures and their captions is just as important as reading through the text itself. t .BOZQIPUPHSBQITIBWFiMPDBUPSNBQTwUPIFMQZPV learn the locations of the many places we mention in the book. t "SFGFSFODFNBQPGQIZTJDBMGFBUVSFTPGUIFXPSMEJT found inside the front cover of the book, and a reference map of the countries of the world is found inside the back cover. t &BDI DIBQUFS CFHJOT XJUI B RVJDL PWFSWJFX PG UIF material, as well as series of questions—think about these questions as you study the material in that chapter. t -PPLBUUIFQIPUPHSBQIUIBUCFHJOTFBDIDIBQUFS5IF Seeing Geographically questions for this photograph will get you thinking about the material in the chapter, and about the kinds of things that geographers can learn by looking at a landscape. t "TZPVSFBEUISPVHIFBDIDIBQUFS ZPVMMDPNFBDSPTT short Learning Check questions. These quick questions are designed to check your understanding of key information in the text section you’ve just read. Answers to the Learning Check questions are found in the back of the book. t &BDI DIBQUFS DPODMVEFT XJUI B Learning Review. Begin with the Key Terms and Concepts questions— these will check your understanding of basic factual information and key terms (key terms are printed in bold type throughout the text). Then, answer the Study Questions—these will confirm your understanding of major concepts presented in the chapter. Finally, you can try the Exercises—for these problems you’ll interpret maps or diagrams and use basic math to reinforce your understanding of the material you’ve studied. t 'JOJTIUIFDIBQUFSCZBOTXFSJOHUIFSeeing Geographically questions at the end of the Learning Review. To answer these questions, you’ll put to use things you’ve learned in the chapter. As you progress through the book, you begin to recognize how much more you can “see” in a landscape after studying physical geography. t 5IF BMQIBCFUJDBM HMPTTBSZ BU UIF FOE PG UIF book provides definitions for all of the key terms. t .PTUDIBQUFSTJODMVEF23DPEFTJDPOTUIBUEJSFDUZPV to online animations and videos that you can access with your mobile device. The animations help explain important concepts in physical geography and include a written and an audio narration. The animations and videos can also be accessed through the Student Study Area in MasteringGeography, and animations can also be assigned for credit by teachers.

THE TEACHING AND LEARNING PACKAGE The author and publisher have been pleased to work with a number of talented people to produce an excellent instructional package.

FOR TEACHERS AND STUDENTS MasteringGeography™ with Pearson eText The Mastering platform is the most widely used and effective online homework, tutorial, and assessment system for the sciences. It delivers self-paced tutorials that provide individualized coaching, focus on course objectives, and are responsive to each student’s progress. The Mastering system helps teachers maximize class time with customizable, easy-to-assign, and automatically graded assessments that motivate students to learn outside of class and arrive prepared for lecture. MasteringGeography offers: t Assignable activities that include Geoscience Animation activities, Encounter Physical Geography Google Earth Explorations, Video activities, MapMaster™ Interactive Map activities, Map Projection activities, coaching activities on the toughest topics in physical geography, end-of-chapter questions and exercises, reading quizzes, Test Bank questions, and more. t Student Study Area with Geoscience Animations, Videos, MapMaster™ interactive maps, web links, glossary flashcards, “In the News” RSS feeds, chapter quizzes, an optional Pearson eText (including versions for iPad and Android devices), and more. Pearson eText gives students access to the text whenever and wherever they can access the Internet. The eText pages look exactly like the printed text, and include powerful interactive and customization functions, including links to the multimedia. Geoscience Animation Library on DVD 5th edition (0321716841) This resource offers over 100 animations covering the most difficult-to-visualize topics in physical geography, physical geology, oceanography, meteorology, and Earth science. The animations are provided as Flash files and preloaded into PowerPoint slides for both Windows and Mac. This library was created through a unique collaboration among Pearson’s leading geoscience authors—including Darrel Hess, Robert Christopherson, Frederick Lutgens, Aurora Pun, Gary Smith, Edward Tarbuck, and Alan Trujillo. Television for the Environment Earth Report Videos on DVD (0321662989) This three-DVD set helps students visualize how human decisions and behavior have affected the environment, and how individuals are taking steps

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toward recovery. With topics ranging from the poor land management promoting the devastation of river systems in Central America to the struggles for electricity in China and Africa, these 13 videos from Television for the Environment’s global Earth Report series recognize the efforts of individuals around the world to unite and protect the planet. Practicing Geography: Careers for Enhancing Society and the Environment by Association of American Geographers (0321811151) This book examines career opportunities for geographers and geospatial professionals in business, government, nonprofit, and educational sectors. A diverse group of academic and industry professionals share insights on career planning, networking, transitioning between employment sectors, and balancing work and home life. The book illustrates the value of geographic expertise and technologies through engaging profiles and case studies of geographers at work. Teaching College Geography: A Practical Guide for Graduate Students and Early Career Faculty by Association of American Geographers (0136054471) This two-part resource provides a starting point for becoming an effective geography teacher from the very first day of class. Part One addresses “nuts-and-bolts” teaching issues. Part Two explores being an effective teacher in the field, supporting critical thinking with GIS and mapping technologies, engaging learners in large geography classes, and promoting awareness of international perspectives and geographic issues. Aspiring Academics: A Resource Book for Graduate Students and Early Career Faculty by Association of American Geographers (0136048919) Drawing on several years of research, this set of essays is designed to help graduate students and early career faculty start their careers in geography and related social and environmental sciences. Aspiring Academics stresses the interdependence of teaching, research, and service—and the importance of achieving a healthy balance of professional and personal life—while doing faculty work. Each chapter provides accessible, forward-looking advice on topics that often cause the most stress in the first years of a college or university appointment.

FOR THE TEACHER t Instructor Resource Manual (032186400X) Available for download, this resource for both new and experienced teachers includes learning objectives, detailed chapter outlines, icebreakers to initiate classroom discussions, answers to end-of-chapter questions and a sample syllabus. t TestGen/Test Bank® (0321863992) TestGen is a computerized test generator that lets teachers view and edit Test Bank questions, transfer questions to tests,

and print the test in a variety of customized formats. This Test Bank includes over 3000 multiple-choice, true/false, and short-answer/essay questions. Questions are correlated against learning outcomes as well as U.S. National Geography Standards and Bloom’s Taxonomy to help teachers to better map the assessments against both broad and specific teaching and learning objectives. The Test Bank is also available in Microsoft Word©, and is importable into Blackboard and WebCT. t Instructor Resource DVD (0321863909) Everything teachers need, where they want it. The Instructor Resource DVD helps make teachers more effective by saving them time and effort. All digital resources can be found in one well-organized, easy-to-access place, and include: Figures—All textbook images as JPGs, PDFs, and PowerPoint Slides Lecture Outline PowerPoint Presentations, which outline the concepts of each chapter with embedded art and can be customized to fit teachers’ lecture requirements CRS “Clicker” Questions in PowerPoint format correlated against U.S. National Geography Standards, chapter specific learning outcomes, and Bloom’s Taxonomy TestGen—The TestGen software, questions, and answers for both MACs and PCs Electronic Files of the Instructor Resource Manual and Test Bank This Instructor Resource content is also available completely online via the Instructor Resources section of www.pearsonhighered.com/irc. t Answer Key to Laborator y Manual (0321864026) Available for download, the answer key provides answers to problem sets presented in the Laboratory Manual: www.pearsonhighered.com/irc. t AAG Community Portal for Aspiring Academics and Teaching College Geography: This website is intended to support community-based professional development in geography and related disciplines. Here you will find activities providing extended treatment of the topics covered in both books. The activities can be used in workshops, graduate seminars, brown bags, and mentoring programs offered on campus or within an academic department. You can also use the discussion boards and contributions tool to share advice and materials with others: www.pearsonhighered.com/aag/. t Course Management: Pearson is proud to partner with many of the leading course management system providers on the market today. These partnerships enable us to provide our testing materials already formatted for easy importation into the powerful Blackboard course management system. Please contact your local Pearson representative for details: www.pearsonhighered.com/elearning/.

xxPreface

FOR THE STUDENT t Physical Geography Laboratory Manual, 11th edition by Darrel Hess (0321863968) This lab manual offers a comprehensive set of more than 45 lab exercises to accompany any physical geography class. The first half covers topics such as basic meteorological processes, the interpretation of weather maps, weather satellite images, and climate data. The second half focuses on understanding the development of landforms and the interpretation of topographic maps and aerial imagery. Many exercises have problems that use Google Earth™, and the lab manual website contains maps, images, photographs, satellite movie loops, and Google Earth™ KMZ files. The 11th edition of the lab manual includes both new and revised exercises, new maps, and expanded use of Google Earth™. www.mygeoscienceplace.com t Goode’s World Atlas (0321652002) Goode’s World Atlas has been the world’s premiere educational atlas since 1923, and for good reason. It features over 250 pages of maps, from definitive physical and political maps to important thematic maps that illustrate the spatial aspects of many important topics. The 22nd edition includes 160 pages of new, digitally produced reference maps, as well as new thematic maps on global climate change, sea level rise, CO2 emissions, polar ice fluctuations, deforestation, extreme weather events, infectious diseases, water resources, and energy production. t D i re P re d i c t i o n s b y M i c h a e l M a n n a n d L e e Kump (0136044352) Periodic reports from the Intergovernmental Panel on Climate Change (IPCC) evaluate the risk of climate change brought on by humans. But the sheer volume of scientific data remains inscrutable to the general public, particularly to those who may still question the validity of climate change. In just over 200 pages, this practical text presents and expands upon the essential findings in a visually stunning and undeniably powerful way to the lay reader. Scientific findings that provide validity to the implications of climate change are presented in clear-cut graphic elements, striking images, and understandable analogies.

PEARSON’S ENCOUNTER SERIES Pearson’s Encounter series provides rich, interactive explorations of geoscience concepts through Google Earth™ activities, exploring a range of topics in regional, human, and physical geography. For those who do not use MasteringGeography, all chapter explorations are available in print workbooks as well as in online quizzes, at www.mygeoscienceplace.com, accommodating different classroom needs. Each exploration consists of a worksheet, online quizzes, and a corresponding Google Earth™ KMZ file: t Encounter Physical Geography Workbook and Website by Jess C. Porter and Stephen O’Connell (0321672526)

t Encounter Geosystems Workbook and Website by Charlie Thomsen (0321636996) t Encounter Earth Workbook and Website by Steve Kluge (0321581296) t Encounter Human Geography Workbook and Website by Jess C. Porter (0321682203) t Encounter World Regional Geography Workbook and Website by Jess C. Porter (0321681754)

ACKNOWLEDGMENTS I offer my great appreciation to illustrator Dennis Tasa. Now in our second edition working together, my admiration for his ability to take my ideas and sketches and turn them into effective and impressive illustrations has only grown. Over the years, scores of colleagues, students, and friends have helped me and the founding author of this book, Tom McKnight, update and improve this textbook. Their assistance has been gratefully acknowledged previously. Here we acknowledge those who have provided assistance in recent years by acting as reviewers of the text and animations that accompany it, or by providing helpful critiques and suggestions: Victoria Alapo, Metropolitan Community College Casey Allen, Weber State University Sergei Andronikov, Austin Peay State University Greg Bierly, Indiana State University Mark Binkley, Mississippi State University Peter Blanken, University of Colorado Margaret Boorstein, Long Island University James Brey, University of Wisconsin Fox Valley David Butler, Texas State University Karl Byrand, University of Wisconsin Sean Cannon, Brigham Young University—Idaho Wing Cheung, Palomar College Jongnam Choi, Western Illinois University Glen Conner, Western Kentucky University Carlos E. Cordova, Oklahoma State University Richard A. Crooker, Kutztown University of Pennsylvania Mike DeVivo, Grand Rapids Community College Bryan Dorsey, Weber State University Don W. Duckson, Jr., Frostburg State University Tracy Edwards, Frostburg State University Steve Emerick, Glendale Community College Doug Foster, Clackamas Community College Basil Gomez, Indiana State University Jerry Green, Miami University—Oxford Michael Grossman, Southern Illinois University— Edwardsville Perry J. Hardin, Brigham Young University

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Ann Harris, Eastern Kentucky University Miriam Helen Hill, Jacksonville State University Barbara Holzman, San Francisco State University Robert M. Hordon, Rutgers University Paul Hudson, University of Texas Catherine Jain, Palomar College Steven Jennings, University of Colorado at Colorado Springs Dorleen B. Jenson, Salt Lake Community College Kris Jones, Saddleback College Ryan Kelly, Lexington Community College Rob Kremer, Metropolitan State College of Denver Kara Kuvakas, Hartnell College Steve LaDochy, California State University Michael Madsen, Brigham Young University—Idaho Kenneth Martis, West Virginia University William (Bill) Monfredo, University of Oklahoma Mandy Munro-Stasiuk, Kent State University Paul O’Farrell, Middle Tennessee State University Thomas Orf, Las Positas College Michael C. Pease, University of New Mexico Stephen Podewell, Western Michigan University Nick Polizzi, Cypress College Robert Rohli, Louisiana State University Anne Saxe, Saddleback College Randall Schaetzl, Michigan State University Jeffrey Schaffer, Napa Valley College John H. Scheufler, Mesa College Robert A. Sirk, Austin Peay State University Dale Splinter, University of Wisconsin—Whitewater Stephen Stadler, Oklahoma State University Herschel Stern, Mira Costa College Jane Thorngren, San Diego State University Timothy Warner, West Virginia University Shawn Willsey, College of Southern Idaho My thanks go out to contributors of new and revised short boxed essays included in this edition: Ted Eckmann of Bowling Green State University, Matt Huber of Syracuse University, Ryan Jensen of Brigham Young University, Michael C. Pease of Central Washington University, Nancy Wilkinson of San Francisco State University, Jennifer Rahn, Samford University, Birmingham, Alabama, Valerie Sloan, University of Colorado at Boulder, and Kenneth Zweibel of George Washington University. Thanks also to Randall Schaetzl of Michigan State University, who contributed a new boxed essay, as well as a detailed review of the material on soils and geomorphology. Special thanks go to Karl Byrand of the University of Wisconsin Colleges and Stephen Stadler of Oklahoma

State University. In addition to contributing essays to this edition, both have long shared their expertise by providing student- and teacher-support materials for this textbook series. I would also like to thank Jess Porter of University of Arkansas at Little Rock, Stephen O’Connell of the University of Central Arkansas, Jason Allard of Valdosta State University, Richard Crooker of Kutztown University, Chris Sutton of Western Illinois University, and Andrew Mercer of Mississippi State University for their contributions to MasteringGeography and other supporting material. Many of my colleagues at City College of San Francisco offered valuable suggestions on sections of the previous and current edition of the book: Carla Grandy, Dack Lee, Joyce Lucas-Clark, Robert Manlove, Kathryn Pinna, Todd Rigg-Carriero, Carole Toebe, and Katryn Wiese. I especially want to thank Chris Lewis, who reviewed large sections of this book for clarity and accuracy. I also extend my appreciation to my many students over the years—their curiosity, thoughtful questions, and cheerful acceptance of my enthusiasm for geography have helped me as a teacher and as a textbook author. Textbooks of this scope cannot be created without a production team that is as dedicated to quality as the authors. First of all, my thanks go to Pearson Geography Editor Christian Botting, who provided skillful leadership and assembled the outstanding group of professionals with whom I worked. My thanks and admiration go to Senior Project Editor Crissy Dudonis, who cheerfully kept me on track throughout the entire production process. Many thanks also to Project Manager Anton Yakovlev, Senior Project Manager Katy Gabel, Production Project Liaison Ed Thomas, Photo Researcher Kristin Piljay, Art Development Editor Jay McElroy, Senior Project Manager Kevin Lear, Assistant Editor Kristen Sanchez, Editorial Assistant Bethany Sexton, Senior Marketing Manager Maureen McLaughlin, Marketing Assistant Nicola Houston, Copyeditor Nicole Schlutt, and Media Producers Tim Hainley and Ziki Dekel. Special thanks go to Marcia Youngman, who has worked as copyeditor or proofreader with me on so many books that I can’t imagine sending a book to press before she’s looked at it. I offer my greatest appreciation to Executive Development Editor Jonathan Cheney, who provided me with unwavering support and sound advice on every aspect of this book. Finally, I wish to express my appreciation for my wife, Nora. Her help, understanding, and support have once again seen me through the long hours and many months of work that went into this book. Darrel Hess Earth Sciences Department City College of San Francisco 50 Phelan Avenue San Francisco, CA 94112 [emailprotected]

DEDICATION

For my wife, Nora D.H.

ABOUT OUR SUSTAINABILITY INITIATIVES Pearson recognizes the environmental challenges facing this planet, as well as acknowledges our responsibility in making a difference. This book is carefully crafted to minimize environmental impact. The binding, cover, and paper come from facilities that minimize waste, energy consumption, and the use of harmful chemicals. Pearson closes the loop by recycling every out-of-date text returned to our warehouse. Along with developing and exploring digital solutions to our market’s needs, Pearson has a strong commitment to achieving carbon-neutrality. As of 2009, Pearson became the first carbon- and climateneutral publishing company. Since then, Pearson remains strongly committed to measuring, reducing, and offsetting our carbon footprint. The future holds great promise for reducing our impact on Earth’s environment, and Pearson is proud to be leading the way. We strive to publish the best books with the most up-to-date and accurate content, and to do so in ways that minimize our impact on Earth. To learn more about our initiatives, please visit www.pearson.com/responsibility.

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ABOUT THE AUTHORS

Darrel Hess began teaching geography at City College of San Francisco in 1990 and served as chair of the Earth Sciences Department from 1995 to 2009. After earning his bachelor’s degree in geography at the University of California, Berkeley, in 1978, he served for two years as a teacher in the Peace Corps on the Korean island of Jeju-do (see Figure 2-24). Upon returning to the United States, he worked as a writer, photographer, and audiovisual producer. His association with Tom McKnight began as a graduate student at UCLA, where he served as one of Tom’s teaching assistants. Their professional collaboration developed after Darrel graduated from UCLA with a master’s degree in geography in 1990. He first wrote the Study Guide that accompanied the fourth edition of Physical Geography: A Landscape Appreciation, and then the Laboratory Manual that accompanied the fifth edition. Darrel has been authoring both works ever since. In 1999 Tom asked Darrel to join him as coauthor of the textbook. As did Tom, Darrel greatly enjoys the outdoor world. Darrel and his wife, Nora, are avid hikers, campers, and scuba divers.

Tom L. McKnight taught geography at UCLA from 1956 to 1993. He received his bachelor’s degree in geology from Southern Methodist University in 1949, his master’s degree in geography from the University of Colorado in 1951, and his Ph.D. in geography and meteorology from the University of Wisconsin in 1955. During his long academic career, Tom served as chair of the UCLA Department of Geography from 1978 to 1983, and was director of the University of California Education Abroad Program in Australia from 1984 to 1985. Passionate about furthering the discipline of geography, he helped establish the UCLA/Community College Geography Alliance and generously funded awards for both undergraduate and graduate geography students. His many honors include the California Geographical Society’s Outstanding Educator Award in 1988, and the honorary rank of Professor Emeritus upon his retirement from UCLA. In addition to Physical Geography: A Landscape Appreciation, his other college textbooks include The Regional Geography of the United States and Canada; Oceania: The Geography of Australia, New Zealand, and the Pacific Islands; and Introduction to Geography, with Edward F. Bergman. Tom passed away in 2004—the geographic community misses him enormously.

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A Learning Path Guides Students Each chapter’s learning tools form a path that gives students a consistent framework to learn about the processes and patterns that create our planet’s landscape. NEW! Seeing Geographically questions at the beginning and end of each chapter ask students to perform visual analysis and critical thinking to check their understanding of key chapter concepts and overcome any misconceptions.

Chapter 2

PORTRAYING EARTH

Seeing Geographically

Seeing Geographically

NEW! Key Questions work as chapter-specific learning outcomes in the chapter opening pages, which connect to Learning Checks, End of Chapter Questions, and the Learning Outcomes in MasteringGeography.™ NEW! Learning Checks integrate review questions at the end of chapter sections, helping students check comprehension.

Learning Check 2-5

Would a Mercator projection be a good choice for a map used to study the loss of forest cover around the world? Why or why not?

Review and Study questions appear at the end of every chapter, giving students the practice they need to learn and master the material. There are three exercise types. t Questions on Key Terms & Concepts ensure students have a firm grasp of the essential vocabulary. t Study Questions reinforce the main concepts in the chapter. t NEW! Exercises offer optional mathematical treatments of chapter concepts, and are also available in MasteringGeography. KEY TERMS AND CONCEPTS

Learning Check 3-6

Is photochemical smog considered a primary pollutant or a secondary pollutant in the atmosphere? Why?

The Nature of Water: Commonplace but Unique (p. 142) 1. Briefly describe how water moves through the hydrologic cycle. 2. What is a hydrogen bond between water molecules? 3. Describe what happens to the density of water as it freezes. 4. What is meant by surface tension of water? 5. What is capillarity?

STUDY QUESTIONS

Learning Check 9-7

What are some of the consequences of thawing permafrost around the Arctic?

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1. Why does ice float on liquid water? 2. Why is evaporation a “cooling” process and condensation a “warming” process? 3. What happens to the relative humidity of an unsaturated parcel of air when the temperature decreases? Why? 4. What happens to the relative humidity of an unsaturated parcel of air when the temperature increases? Why? 5. Why does a rising parcel of unsaturated air cool at a greater rate than a rising parcel of saturated air (in EXERCISES which condensation is taking place)? 1. Calculate the relative humidity for the following parcels of air: a. If the specific humidity is 5 g/kg and the capacity is 20 g/kg: __________ % b. If the specific humidity if 35 g/kg and the capacity is 40 g/kg: __________ % 2. Use Figure 6-8 to estimate the water vapor capacity (the saturation specific humidity in g/kg) of air at the following temperatures: a. 0°C (32°F): __________ g/kg b. 30°C (86°F): __________ g/kg 3. Using your answers for Exercise Problem 2 above, calculate the relative humidity of the following parcels of air at the temperature given: a. If the specific humidity is 3 g/kg at a temperature of 0°C: __________%

Current, Compelling Applications Boost Comprehension Expert contributors author many of the special Focus, People and the Environment, and Energy for the 21st Century features, sharing a variety of expertise and experience with students. NEW! Energy for the 21st Century feature boxes provide balanced coverage of both renewable and non-renewable energy resources authored by expert contributors, including a new feature on Our Continuing Dependence on Fossil Fuels (Chapter 3) and Fracking for Natural Gas (Chapter 13).

People and the Environment boxes discuss the effects of human activity on the environment. New topics in the Eleventh Edition include The Record Breaking Tornadoes of 2011 (Chapter 7) and the 2010 Haiti Earthquake (Chapter 14).

PEOPLE AND THE ENVIRONMENT ENERGY FOR THE 21ST CENTURY

The Devastating Tornadoes of 2011

Our Continuing Dependence on Fossil Fuels

▶ Ted Eckmann, Bowling Green State University

▶ Matthew T. Huber, Syracuse University

F

ossil fuels (coal, oil, and natural gas) are the product of millions of years of accumulated solar energy absorbed in plant life and trapped as hydrocarbon matter underneath Earth’s surface.

The Historical Significance of Fossil Fuels: Before the use of fossil fuels, people did most mechanical work using their own muscle power and that of animals both ultimately derived from the energy of sunshine stored in plants through photosynthesis and the animals that consume plants (discussed in Chapter 10). The historic shift from solar energy to fossil fuels led to machinery that ran without the force of muscle power, such as steam engines, and eventually to electrical power generation and automobiles. This change allowed for dramatic gains in labor productivity and the growth of transportation networks. Moreover, the increasing reliance on fossil fuels freed up thousands of acres that were previously used for energy, such as farmland used to grow feed for working animals and forest land that provided wood and charcoal for heating, cooking, and metal production. Because of these benefits, the world today derives around 80 percent of its energy from fossil fuels (Figure 3-C).

The Consequences of Fossil Fuel Use: Despite the benefits of fossil fuels, they are not without drawbacks. First, the combustion of coal, oil, and gas produces enormous amounts of pollution. For example, sulfur dioxide (SO2) from coal-fired power plants causes acid rain

(discussed in Chapter 6). All fossil fuel use emits carbon dioxide (CO2), a greenhouse gas associated with global climate change (discussed in Chapter 4). Moreover, the uneven distribution of fossil fuels creates geopolitical conflict over access to, and control over, energy resources. Although this problem is most visible in conflicts over oil (as in the Middle East), conflicts over natural gas pipelines in the Ukraine and North America and concerns about “fracking” in the United States (see Chapter 13) or mountaintop coal mining in Appalachia represent other examples of the contentious nature of fossil fuel development.

Alternative Energy: Since at least the 1970s, support for switching to alternative energy has been growing among scientists, policymakers, and the public. Most alternatives to fossil fuels generate electricity. Most electricity today is generated by the combustion of coal or gas to create steam that turns a turbine. For now, the transportation sector runs mostly on liquid fuels derived from crude oil. The only liquid fuel alternatives are biofuels (see Chapter 10), often derived from crops grown on farmland, thus competing with food production. Many alternative energy sources show promise but also have limitations. Nuclear power is the largest alternative energy source, but it brings risks of calamitous accidents, such as the Fukushima disaster in Japan following the tsunami of 2011 (see Chapter 20), and produces radioactive waste Hydro 2.3%

T

he tornadoes of 2011 shattere many long-standing records an demonstrated that despite advance in detection and warning technolog tornadoes still pose major threat Prior to 2011, the record for the larg est number of tornadoes in a singl month stood at 542, but April 201 surpassed this in dramatic fashio with 758 tornadoes reported acros the United States. The most activ part of the month was from Apr 25 to April 28, and it included th d e a d l i e s t t o r n a d o o u t b re a k s i n c modern recordkeeping began. Th outbreak produced 343 confirmed tornadoes and killed 321 people (Figure 7-E). Damage likely exceeded 10 billion dollars. Four of these tornadoes produced damage up to the EF-5 category—the first EF-5 tornadoes anywhere on Earth since 2008. However, these storms would not be the last tornadoes to reach EF-5 strength in this record-breaking year.

that is difficult to dispose of. Hydroelectric power uses dams and the power of falling water to generate electricity (see Chapter 16). Dams, however, degrade river ecosystems and often displace thousands of people. Wind power recently has been the fastest growing alternative (see Chapter 5), but its capacity to generate electricity ultimately depends on when the wind blows. Solar power harnesses direct sunlight to generate electricity either through photovoltaic cells or the boiling of water to create steam (see Chapter 4). Like wind, solar is intermittent, and it is not available when it is dark or cloudy. Furthermore, unlike fossil fuels that can be easily transported anywhere, some alternatives such as geothermal (see Chapter 17) and tidal power (see Chapter 20), as well as large installations of wind and solar power generation, may only be available in locations far from population centers, such as deserts for solar and unobstructed topography for wind. Most importantly, the main barriers to an “energy transition” away from fossil fuels are political and economic (see Chapter 8). Historically, fossil fuels are simply much cheaper making it difficult for alternative energy to be economically viable when only short-term costs are considered. Fossil fuel energy companies are also some of the largest and most profitable corporations in the world, and some have used their political influence to inhibit policies that might spur a shift toward alternative energy.

EF-5 Tornadoes:

Although EF-5 is the rarest ranking for a tornado, EF5s produce a disproportionately large share of overall tornado fatalities because they can destroy even well-built structures. Thus, even people in shelters who would be adequately protected from weaker tornadoes sometimes die in EF-5 strength winds, which can be the fastest on Earth. All four of the EF-5 tornadoes in Figure 7-E occurred on the same day—April 27, 2011—that set a new record for the largest number of confirmed tornadoes in a 24-hour period: 199. The largest of the EF-5 tornadoes from April 27 remained on the ground for almost 2 hours, producing a damage path 172 kilometers (107 miles) long and up to 2 kilometers (1.25 miles) wide.

Other* 0.8%

Nuclear 5.8% Oil 32.8%

Biofuels and waste 10.2%

VA

NC

EF-5 EF-4 EF-3 EF-2 EF-1 EF-0

m April 25 to 28, 2011, color-coded by maximum intensity reached along the path. only 36 kilometers (22 miles). However, the Joplin tornado reached its peak strength in a densely populated city of around 50,000 residents. Most of the areas affected in the April outbreak had substantially lower population densities, and although parts of urban areas like Tuscaloosa and Birmingham, Alabama, did experience EF-4 level damage, the EF-5 tornadoes in the April outbreak mostly occurred outside large cities. The Joplin tornado’s combination of EF-5 strength with a densely populated

area produced catastrophic results. It killed 158 people and caused three billion dollars of damage, making it the most destructive and most deadly tornado since modern recordkeeping began. Tornadoes occurred in seven other states on the same day as the Joplin tornado, but the Joplin tornado was the day’s only EF-5, and the totals for destruction and fatalities from that day remained well below the records set in the April outbreak a few weeks earlier.

Lessons Learned:

By the end of 2011, tornadoes had killed 551 people in the United States—the largest annual total in 62 years of modern records. Even though weather forecasting and warning technologies have improved dramatically over the last 62 years, population densities have also increased, and studies have found that some people may even be taking tornadoes less seriously than they did in the past—education and communication about tornado hazards remain important components of public safety during severe storms.

Joplin Tornado:

Less than one month later, on May 22, another EF-5 tornado occurred, this time in Joplin, Missouri (Figure 7-F). In comparison to many of the tornadoes from the April outbreak, the EF-5 in Joplin was relatively compact, with a path length of

Natural gas 20.9% Coal/peat 27.2%

▲ Figure 7-F Damage in Joplin, Missouri, two days after an EF-5 tornado

devastated the city.

▲ Figure 3-CSources of global energy production in 2009. “Other” includes geothermal, solar, wind, and tidal power. (Source: International Energy Agency, 2011, Key World Energy Statistics 2011.)

FOCUS

Using Remote Sensing Images to Study a Landscape ▶ Ryan Jensen, Brigham Young University

R

Focus features present in-depth case studies of special topics in physical geography. New topics in the Eleventh Edition include Using Remote Sensing Images to Study a Landscape (Chapter 2), The Conveyor Belt Model of Midlatitude Cyclones (Chapter 7), and Monitoring Groundwater Resources from Space (Chapter 9).

emote sensing provides geographers and other researchers with a great amount of spatial information that can be analyzed to improve our understanding of landscapes. Geographers can study spatial features using data collected from both aerial platforms (airplanes or helicopters) and orbital platforms (satellites). Popular websites and programs provide much remote sensing data for anyone to examine at no cost. These programs, such as Google Earth™, MapQuest™, and the U.S. Geological Survey National Map, are valuable tools that display data at a variety of scales, depending on the “Zoom” level you select. Spatial resolution (the amount of detail you can see) becomes finer the further you zoom into a landscape. The usefulness of remote sensing will only increase as human activities and natural processes change Earth’s surface.

A Fluvial Landscape:

To see how remote sensing data can capture characteristics of Earth’s surface, look at the images of fluvial features (features formed by flowing water) in Figure 2-A. Landsat 5 acquired the data for the Costa Marques, Brazil, area in June 1984 and again in September 2001. Costa Marques is located along the Guapore/ Itenez River that forms the border between Brazil and Bolivia. Landsat data are typically acquired in 30 * 30 meter pixels. That is, each image pixel covers an area of 30 meters by 30 meters (98 feet by 98 feet), or 900 square meters

(9687 square feet) over a surface area of 180 kilometers by 180 kilometers (111 miles by 111 miles). In each of the images, you can see fluvial features such as meanders, meander scars, oxbow lakes, and floodplain lakes. The images can also be compared to study changes in the landscape. Notice that the rivers are much wider and there is more water on the floodplains in the 1984 scene than in the 2001 scene. Further, many of the oxbow lakes (Point A) had much more water in 1984 than in 2001. Meander scars that were very obvious in 1984 (Point B) are not as obvious in 2001. Sand that was not visible in 1984 (Point C) is visible in 2001. The 2001 image also shows evidence of human expansion in Costa Marques and along parts of the Guapore/Itenez River (Points D and E).

A More Detailed Look:

When more detail is needed, finer spatial resolution data may be used to study an area. Such data are available from commercial

B F

▲ Figure 2-B Fine-spatial resolution data showing a meander neck and meander scars in the Costa Marques area. September 2001

June 1984

D

D

Costa Marques

E

Guapore/Itenez River

C

B

websites and programs such as Google Earth, MapQuest, and many others. For example, look at Point F in Figure 2-A. It is reasonable to assume that the river at that point will eventually create a new channel across the neck of the meander. This process cannot be clearly examined using the 30 * 30 meter Landsat data, but it can be examined using finer-resolution data. Figure 2-B shows a more-detailed image of the same meander neck at Point F. As you can see, there might be evidence of a new channel forming at Point F. In fact, in wet years, river water may flow through the meander neck. Consider another example: Point B in Figure 2-B shows the same meander scars as the Landsat images in Figure 2-A (Point B). These features can be more fully examined using the detailed image in Google Earth, which can also be used to make measurements such as length and area. Knowing the area of the lake within the scar might be useful in determining how the lake changes from season to season or year to year.

B

A F

Costa Marques

Guapore/Itenez River

C

A

E

◀ Figure 2-A Two

F

Landsat images acquired over the Costa Marques, Brazil, area in 1984 and 2001.

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Dynamic Media to Engage Students Multimedia resources are linked throughout the text and eText, bringing the concepts to life.

Animation Convection and Plate Tectonics

NEW! Quick Response (QR) Codes within the pages of the book link to a variety of animations and videos, providing students with just-in-time access to media resources tied to the book’s concepts. Media are automatically linked in the eText and also available in the MasteringGeography™ study area.

Video Hurricane Hot Towers

NEW! Additional satellite images, the latest science, statistics, and associated graphics are integrated throughout the text. These resources provide a clear, relevant view of the planet as we understand it and encourage students to explore on their own.

▲Figure 3-24 The wind pattern within storms such as hurricanes is

influenced by the deflection of the Coriolis effect. This image shows Tropical Storm Beryl in May 2012, just before making landfall.

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Stunning Graphics Visualize Earth’s Landscape The excellent cartographic and illustration program by renowned geoscience illustrator Dennis Tasa helps students visualize and understand the concepts covered in this text. Hundreds of maps include shaded relief where appropriate.

Major photos paired with locator maps to enhance geographic literacy.

NEVADA

UTAH

(a) High-resolution orthoimagery Lake Mead

Hoover Dam

(b) Topographic map

C

r olo

ad o R .

Lake Mohave CALIFORNIA

ARIZONA

“Bathtub ring” from higher reservoir level

(c) Geologic map (d) Google map ▲Figure 2-1 Different types of maps convey different kinds of information about the landscape, as shown in

these four maps of a region near Salem, Massachusetts. (a) High-resolution orthophoto imagery (original scale 1:24,000). (b) Topographic map with elevation contour lines (original scale 1:24,000). (c) Geologic map showing rock types: orange = coarse glacial deposits; blue = glaciomarine deposits; green = glacial till; lavender = swamp deposits (original scale 1:50,000). (d) Google™ Map showing streets and highways.

Midocean ridge Transform fault

Oceanic crust

Seafloor spreading

Lithosphere

▲Figure 9-24 Hoover Dam and Lake Mead on the Colorado River. The

“bathtub ring” around the margin of the reservoir marks the water level when Lake Mead is at full capacity.

Continental crust Asthenosphere

(a) Transform plate boundary

(b) Divergent plate boundary

Oceanic trench

Oceanic crust

Oceanic crust

Continental crust Lithosphere

g

(c) Convergent plate boundary (oceanic–oceanic subduction)

Oceanic crust

Lithosphere

e

tin

Asthenosphere

Oceanic trench

Lithosphere

Figure 14.12

Line art with numerous multi-part photorealistic illustrations capture sequence and evolution to help students understand various processes.

lat

Continental crust Lithosphere

Su

p

bd

uc

bd

Asthenosphere

Su

uc

tin

gp

lat

e

(d) Convergent plate boundary (oceanic–continental subduction)

▲Figure 14-12 Three kinds of plate boundaries. The edges of lithospheric plates slide past each

other along transform boundaries such as the San Andreas Fault system in California (a); move apart at divergent boundaries such as continental rift valleys and midocean ridges (b); and come together at convergent boundaries such as oceanic-oceanic plate subduction zones (c), oceaniccontinental plate subduction zones (d), and continental collision zones.

xxvii

www.masteringgeography.com MasteringGeography delivers engaging, dynamic learning opportunities—focusing on course objectives and responsive to each student’s progress—that are proven to help students absorb physical geoscience course material and understand difficult geographic concepts. Give students a sense of place and an understanding of physical concepts Encounter Activities provide rich, interactive explorations of geography concepts using the dynamic features of Google Earth™ to visualize and explore Earth’s physical landscape. Dynamic assessment includes multiple-choice and shortanswer questions related to core physical geography concepts. All Explorations include corresponding Google Earth KMZ media files, and questions include hints and specific wrong-answer feedback to help coach students towards mastery of the concepts.

Geoscience Animations illuminate the most difficultto-visualize topics from across the physical geosciences, such as solar system formation, hydrologic cycle, plate tectonics, glacial advance and retreat, global warming, etc. Animations include audio narration, a text transcript, and assignable multiple-choice quizzes with specific wrong-answer feedback to help guide students towards mastery of these core physical process concepts. NEW! Quick Response Codes link to video and animation resources as a means to provide students with just-intime access to visualization or indicate to students when they can login to the Study Area of MasteringGeography to access these media.

xxviii

Improve critical thinking and geographic literacy while exploring Earth’s physical landscape is a powerful tool that presents assignable layered thematic and place name interactive maps at world and regional scales for students to test their geographic literacy and spatial reasoning skills, and explore the modern geographer’s tools. MapMaster Layered Thematic Interactive Map Activities act as a mini-GIS tool, allowing students to layer various thematic maps to analyze spatial patterns and data at regional and global scales. Multiple-choice and short-answer questions are organized around the textbook topics and concepts. NEW! MapMaster has been updated to include: tOFXNBQMBZFST t;PPNBOEBOOPUBUJPO functionalities t$VSSFOU64$FOTVT 6OJUFE Nations, and Population Reference Bureau Data

NEW! Coaching Activities are built around the toughest topics in physical geography. Geography videos provide students a sense of place and allow them to explore a range of locations and topics related to physical geography. A variety of video clips cover diverse locations and physical geoscience concepts, with quiz questions to make these assignable and assessable. These video activities allow instructors to test students’ understanding and application of concepts, and offer hints and wrong-answer feedback to guide students towards mastering the concepts.

Student Resources in MasteringGeography t t t t t t t

(FPTDJFODF"OJNBUJPOT .BQ.BTUFS™ interactive maps 1SBDUJDFRVJ[[FT (FPHSBQIZWJEFPT i*OUIF/FXTw344GFFET (MPTTBSZGMBTIDBSET 0QUJPOBM1FBSTPOF5FYUBOENPSF

Callouts to MasteringGeography appear at the end of each chapter to direct students to extend their learning beyond the textbook. xxix

www.masteringgeography.com With the Mastering gradebook and diagnostics, you’ll be better informed about your students’ progress than ever before. Mastering captures the step-by-step work of every student—including wrong answers submitted, hints requested, and time taken at every step of every problem—all providing unique insight into the most common misconceptions of your class. Quickly monitor and display student results

The Gradebook records all scores for automatically graded assignments. Shades of red highlight struggling students and challenging assignments.

Diagnostics provide unique insight into class and student performance. With a single click, charts summarize the most difficult questions, vulnerable students, grade distribution, and score improvement over the duration of the course.

With a single click, Individual Student Performance Data provides at-a-glance statistics into each individual student’s performance, including time spent on the question, number of hints opened, and number of wrong and correct answers submitted.

xxx

Easily measure student performance against your Learning Outcomes Learning Outcomes MasteringGeography provides quick and easy access to information on student performance against your learning outcomes and makes it easy to share those results. t 2VJDLMZBEEZPVSPXOMFBSOJOHPVUDPNFT PSVTFQVCMJTIFS provided ones, to track student performance and report it to your administration. t 7JFXDMBTTBOEJOEJWJEVBMTUVEFOUQFSGPSNBODFBHBJOTU specific learning outcomes. t &GGPSUMFTTMZFYQPSUSFTVMUTUPBTQSFBETIFFUUIBUZPVDBO further customize and/or share with your chair, dean, administrator, and/or accreditation board.

Easy to customize Customize publisher-provided items or quickly add your own. MasteringGeography makes it easy to edit any questions or answers, import your own questions, and quickly add images, links, and files to further enhance the student experience. Upload your own video and audio files from your hard drive to share with students, as well as record video from your computer’s webcam directly into MasteringGeography—no plugins required. Students can download video and audio files to their local computer or launch them in Mastering to view the content.

Pearson eText gives students access to McKnight’s Physical Geography: A Landscape Approach, Eleventh Edition whenever and wherever they can access the Internet. The eText pages look exactly like the printed text, and include QPXFSGVMJOUFSBDUJWFBOEDVTUPNJ[BUJPOGVODUJPOT6TFST can create notes, highlight text in different colors, create bookmarks, zoom, click hyperlinked words and phrases to view definitions, and view as a single page or as two pages. Pearson eText also links students to associated media files, enabling them to view an animation as they read the text, and offers a full-text search and the ability to save and export OPUFT5IF1FBSTPOF5FYUBMTPJODMVEFTFNCFEEFE63-TJO the chapter text with active links to the Internet. NEW! The Pearson eText app is a great companion to Pearson’s eText browser-based book reader. It allows existing subscriberswho view their Pearson eText titles on a Mac or PC to additionally access their titles in a bookshelf on the iPad and Android devices either online or via download. xxxi

Chapter 1

INTRODUCTION TO EARTH

IF YOU OPENED THIS BOOK EXPECTING THAT THE STUDY OF geography was going to be memorizing names and places on maps, you’ll be surprised to find that geography is much more than that. Geographers study the location and distribution of things—tangible things such as rainfall, mountains, and trees, as well as less tangible things such as language, migration, and voting patterns. In short, geographers look for and explain patterns in the physical and human landscape. In this book you’ll learn about fundamental processes and patterns in the natural world—the kinds of things you can see whenever you walk outside: clouds in the sky, mountains, streams and valleys, and the plants and animals that inhabit the landscape. You’ll also learn about human interactions with the natural environment—how events such as hurricanes, earthquakes, and floods affect our lives and the world around us, as well as how human activities are increasingly altering our environment. By the time you finish this book you’ll understand—in other words you’ll appreciate—the landscape in new ways. This opening chapter sets the stage for your study of physical geography. Here we introduce concepts and terms used throughout the book. As you study this chapter, think about these key questions: S How do geographers study the world and use science to explain and understand the

natural environment? S What are the overlapping environmental “spheres” of Earth, and how does the

concept of Earth systems help us understand the interrelationships of these spheres? S How does Earth fit in with the solar system, and how does the size of Earth compare

with the size of its surface features? S How does the system of latitude and longitude describe location on Earth? S What causes the annual change of seasons, and how do patterns of sunlight around

Earth change during the year? S How is the system of time zones used to establish times and dates around the

world?

GEOGRAPHY AND SCIENCE The word geography comes from the Greek words meaning “Earth description.” Several thousand years ago many scholars were indeed “Earth describers,” and therefore geographers, more than anything else. Nonetheless, over the centuries there was a trend away from generalized Earth description toward more specialized disciplines—such as geology, meteorology, economics, and biology—and so geography as a field of study was somewhat overshadowed. Over the last few hundred years, however, geography reaffirmed its place in the academic world, and today geography is an expanding and flourishing field of study.

Seeing Geographically This is a natural color, composite satellite image of Earth created by NASA. In the image can you see any indications of human presence? What might explain the differences in the color of land areas? What might explain the differences in the color of ocean areas?

3

4Physical Geography: A Landscape Appreciation

All of the items shown in Figure 1-1 are familiar to us, and this familiarity highlights a basic characteristic of geography as a field of learning: Geography doesn’t have its own body of facts or objects that only geographers study. The focus of geology is rocks, the attention of economics is economic systems, demography examines human population, and so on. Geography, on the other hand, is much broader in scope than most other disciplines, “borrowing” its objects of study from related fields. Geographers, too, are interested in rocks and economic systems and population—especially in describing and understanding their location and distribution. We sometimes say that geography asks the fundamental question, “Why what is where and so what?”

Elements of Geography Physical Geography

Cultural Geography

Landforms

Population

Rocks & Minerals

Economic Activities

Water

Languages

Weather & Climate

Religions Political Systems

Plants Animals

Settlements Soil

Food

Natural Science

Learning Check 1-1

What are the differences between physical geography and cultural geography? (Answer on p. AK-1)

Social Science

▲Figure 1-1 The elements of geography can be grouped into two broad

categories. Physical geography primarily involves the study of natural science, whereas cultural geography primarily entails the study of social science.

Another basic characteristic of geography is its interest in interrelationships. One cannot understand the distribution of soils, for example, without knowing something about the rocks from which the soils were derived, the slopes on which the soils developed, and the climate and vegetation under which they developed. Similarly, it is impossible to comprehend the distribution of agriculture without an understanding of climate, topography, soil, drainage, population, economic conditions, technology, historical development, and many other factors, both physical and cultural. Because of its wide scope, geography bridges the academic gap between natural science and social science, studying all of the elements in Figure 1-1 in an intricate web of geographic interrelationships. In our study of physical geography, our emphasis is on understanding the surface environment of Earth and the ways in which humans utilize and alter this environmental home. The habitable environment for humans exists over almost the entire land surface of Earth (Figure 1-2). It is only in the most extremely dry, cold, and rugged places

Studying the World Geographically Geographers study how things differ from place to place—the distributional and locational relationships of things around the world (what is sometimes called the “spatial” aspect of things). Figure 1-1 shows the kinds of “things” geographers study, divided into two groups representing the two principal branches of geography. The elements of physical geography are natural in origin, and for this reason physical geography is sometimes called environmental geography. The elements of cultural geography are those of human endeavor, so this branch is sometimes referred to as human geography. The almost unlimited possible combinations of these various elements create the physical and cultural landscapes of the world that geographers study.

◀Figure 1-2 Most of Earth’s land surface 60°

is habitable. The uninhabitable areas are too hot, too cold, too wet, too dry, or too rugged to support much human life—such as parts of the Arctic, most of Greenland, Antarctica, various mountainous regions, and several deserts.

60°

PA C I F I C OCEAN

ATLANTIC

30°

OCEAN

Tropic of Cancer

30° Tropic of Cancer PA C I F I C OCEAN

Equator

INDIAN

Equator

OCEAN PA C I F I C Tropic of Capricorn

OCEAN

Tropic of Capricorn

30°

30°

Habitable Nonhabitable

30° INDIAN

ATLANTIC OCEAN

OCEAN 0 0

60°

MODIFIED GOODE'S HOMOLOSINE EQUAL-AREA PROJECTION

60°

1000

2000

3000 Miles

3000 Kilometers 60°

CHAPTER 1Introduction to Earth5

that humans rarely venture, and even in such locations, other forms of life may be found. Earth’s “life zone,” encompassing oceanic, terrestrial, and atmospheric life, extends from the bottom of the deepest oceanic trench to the atmosphere above the highest mountain peaks—a zone perhaps 30 kilometers (20 miles) deep. It is primarily within this shallow life zone that geographers focus their interests and do their work. In this book we concentrate on the physical elements of the landscape, the processes involved in their development, their distribution, and their basic interrelationships. As we proceed from chapter to chapter, this notion of landscape development by natural processes and landscape modification by humans serves as a central focus. We will pay attention to elements of cultural geography only when they help to explain the development or patterns of the physical elements—especially the ways in which humans influence or alter the physical environment. Global Environmental Change:Several broad geographic themes run through this book. One of these themes is global environmental change—both the humancaused and natural processes that are currently altering the landscapes of the world. Some of these changes can take place over a period of just a few years, whereas others require many decades or even thousands of years (Figure 1-3). We pay special attention to the accelerating impact of human activities on the global environment: In the chapters on the atmosphere we discuss such issues as human-caused climate change, ozone depletion, and acid rain, whereas in later chapters we look at issues such as rainforest removal and coastal erosion. Rather than treat global environmental change as a separate topic, we integrate this theme throughout the book. To help with this integration, we supplement the main text with short boxed essays, such as those entitled “People and the Environment” that focus on specific cases of human interaction with the natural environment, as well as boxes entitled “Energy for the 21st Century” that

focus on the challenge of supplementing—and perhaps eventually replacing—fossil fuels with renewable sources of energy. These essays serve to illustrate the connections between many aspects of the environment, such as the relationships between changing global temperatures, changing sea level, changing quantities of polar ice, and the changing distribution of plant and animal species, and the global economy and human society. Globalization:A related but less obvious theme running through this book is globalization. In the broadest terms, globalization refers to the processes and consequences of an increasingly interconnected world— connections between the economies, cultures, and political systems of the world. Although globalization is most commonly associated with the cultural and economic realms of world, it is important to recognize the environmental components of globalization as well. For example, the loss of tropical rainforest for timber or commercial agriculture in some regions of the world is driven in part by growing demand for commodities in countries far away from the tropics (Figure1-4). Similarly, rapid economic growth in newly industrialized countries is contributing to the already high atmospheric greenhouse gas emissions of industrialized countries—the interconnected economies of the world are thus interconnected in their influence on the natural environment. Because of geography’s global perspective and its interest in both the natural and human landscape, geographers are able to offer insights into many of the world’s most pressing problems—problems too complex to address from a narrower perspective. For example, the detrimental consequences of climate change cannot be addressed if we ignore the economic, social, historical, and political aspects of the issue. Similarly, global inequities of wealth and political power cannot be addressed if we ignore environmental and resource issues. Just about everything in the world is in one way or another connected with everything else! Geography helps us understand these connections. ◀Figure 1-3

Earth’s climate is changing. This image shows the difference in temperature (the temperature anomaly in °C) during the period 2000 to 2009 compared with the average temperatures for the baseline period 1951 to 1980. (NASA)

Temperature Anomaly (°C) –2.5

–1.5

–0.5

+0.5

+1.5

+2.5

▲Figure 1-4 Deforestation in some parts of the tropics is influenced by consumer demand in other parts of the world. This logging operation is in Perak, Malaysia.

Learning Check 1-2

Why are physical geographers interested in globalization?

The Process of Science Because physical geography is concerned with processes and patterns in the natural world, knowledge in physical geography is advanced primarily through the study of science, and so it is useful for us to say a few words about science in general. Science is often described—although somewhat simplistically—as a process that follows the scientific method: 1. Observe phenomena that stimulate a question or problem. 2. Offer an educated guess—a hypothesis—about the answer. 3. Design an experiment to test the hypothesis. 4. Predict the outcome of the experiment if the hypothesis is supported, and if the hypothesis is not supported. 5. Conduct the experiment and observe what actually happens. 6. Draw a conclusion or formulate a simple generalized “rule” based on the results of the experiment. In practice, however, science doesn’t always work through experimentation; in many fields of science, data collection through observation of a phenomenon is the basis of knowledge. In some regards science is best thought of as a process—or perhaps even as an attitude— 6

for gaining knowledge. The scientific approach is based on observation, experimentation, logical reasoning, skepticism of unsupported conclusions, and the willingness to modify or even reject long-held ideas when new evidence contradicts them. For example, up until the 1950s most Earth scientists thought it impossible that the positions of continents could change over time; however, as we’ll see in Chapter 14, by the late 1960s enough new evidence had been gathered to convince them that their earlier ideas were wrong—the configuration of continents has changed, and continues to change! Although the term “scientific proof” is sometimes used by the general public, strictly speaking, science does not “prove” ideas. Instead, science works by eliminating alternative explanations—eliminating explanations that aren’t supported by evidence. In fact, in order for a hypothesis to be “scientific,” there must be some test or possible observation that could disprove it—if there is no way to disprove an idea, then that idea simply cannot be supported by science. The word “theory” is often used in everyday conversation to mean a “hunch” or conjecture. However, in science a theory represents the highest order of understanding for a body of information—a logical, welltested explanation that encompasses a wide variety of facts and observations. Thus, the “theory of plate tectonics” presented in Chapter 14 represents an empirically supported, broadly accepted, overarching framework for understanding processes operating within Earth.

CHAPTER 1Introduction to Earth7

The acceptance of scientific ideas and theories is based on a preponderance of evidence, not on “belief” and not on the pronouncements of “authorities.” New observations and new evidence often cause scientists to revise their conclusions and theories or those of others. Much of this self-correcting process for refining scientific knowledge takes place through peer-reviewed journal articles. Peers—that is, fellow scientists—scrutinize a scientific report for sound reasoning, appropriate data collection, and solid evidence before it is published; reviewers need not agree with the author’s conclusions, but they strive to ensure that the research meets rigorous standards of scholarship before publication. Because new evidence may prompt scientists to change their ideas, good science tends to be somewhat cautious in the conclusions that are drawn. For this reason, the findings of many scientific studies are prefaced by phrases such as “the evidence suggests,” or “the results most likely show.” In some cases, different scientists interpret the same data quite differently and so disagree in their conclusions. Frequently, studies find that “more research is needed.” The kind of uncertainty sometimes inherent in science may lead the general public to question the conclusions of scientific studies—especially when presented with a simple, and perhaps comforting nonscientific alternative. It is, however, this very uncertainty that often compels scientists to push forward in the quest for knowledge and understanding! In this book we present the fundamentals of physical geography as it is supported by scientific research and evidence. In some cases, we will describe how our current understanding of a phenomenon developed over time; in other cases we will point out where uncertainty remains, where scientists still disagree, or where intriguing questions still remain.

TABLE 1-1

Distance:

Unit Conversions—Quick Approximations S.I. to English Units

English to S.I. Units

1 centimeter = a little less than ½ inch

1 inch = about 2½ centimeters

1 meter = a little more 1 foot = about 1⁄3 meters than 3 feet 1 kilometer = about 2⁄3 1 yard = about mile 1 meter 1 mile = about 1½ kilometers Volume:

1 liter = about 1 quart

1 quart = about 1 liter 1 gallon = about 4 liters

Mass:

1 gram = about 1⁄30 ounce

1 ounce = about 30 grams

1 kilogram = about 2 pounds

1 pound = about ½ kilogram

Temperature: 1°C change = 1.8°F change

1°F change = about 0.6°C change

For exact conversion formulas, see Appendix I.

International; also sometimes called the “metric system”)— using measurements such as kilometers, kilograms, and degrees Celsius. You will notice that this book gives measurements in both S.I. and English units. If you are not familiar with both systems, Table 1-1 provides some quick approximations to help you learn the basic equivalents in each; detailed tables of conversion formulas between English and S.I. units appear in Appendix I.

Learning Check 1-3

Why is the phrase “scientific proof” somewhat misleading?

Numbers and Measurement Systems Because so much of science is based on observation and measurable data, any thorough study of physical geography entails the use of mathematics. Although this book introduces physical geography primarily in a conceptual way without the extensive use of mathematical formulas, numbers and measurement systems are nonetheless important for us. Throughout the book, we use numbers and simple formulas to help illustrate concepts—the most obvious of which are numbers used to describe distance, size, weight, and temperature. Two quite different systems of measurement are used around the world today. In the United States much of the general public is most familiar with the so-called English System of measurement—using measurements such as miles, pounds, and degrees Fahrenheit. However, most of the rest of the world—and the entire scientific community—uses the International System of measurement (abbreviated S.I. from the French Système

ENVIRONMENTAL SPHERES AND EARTH SYSTEMS From the standpoint of physical geography, the surface of Earth is a complex interface where four principal components of the environment meet and to some degree overlap and interact (Figure 1-5). These four components are often referred to as Earth’s environmental spheres.

Earth’s Environmental Spheres The solid, inorganic portion of Earth is sometimes called the lithosphere1 (litho is Greek for “stone”), comprising the rocks of Earth’s crust as well as the unconsolidated particles of mineral matter that overlie the solid bedrock. The lithosphere’s surface is shaped into an almost infinite variety of landforms, both on the seafloors and on the surfaces of the continents and islands. 1 As we will see in Chapter 13, in the context of plate tectonics and our study of landforms, the term “lithosphere” is used specifically to refer to large “plates” consisting of Earth’s crustal and upper mantle rock.

8Physical Geography: A Landscape Appreciation

hydrosphere and yet may contain a vast quantity of fish and other organic life that are part of the biosphere. An even better example is soil, which is composed largely of bits of mineral matter (lithosphere) but also contains life forms (biosphere), along with air (atmosphere), soil moisture (hydrosphere), and perhaps frozen water (cryosphere) in its pore spaces. The environmental spheres can serve to broadly organize concepts for the systematic study of Earth’s physical geography and are used that way in this book.

Atmosphere

Cryosphere

Learning Check 1-4

Lithosphere

Briefly define the lithosphere, atmosphere, hydrosphere, cryosphere, and biosphere.

Earth Systems Biosphere ARCTIC OCEAN U.S. CAN.

Alaska Wonder Lake and Mt. McKinley BERING SEA

Hydrosphere

PACIFIC OCEAN

▲Figure 1-5 The physical landscape of Earth is composed of four

overlapping and interacting systems called “spheres.” The atmosphere is the air we breathe. The hydrosphere is the water of rivers, lakes, and oceans, the moisture in soil and air, as well as the snow and ice of the cryosphere. The biosphere is the habitat of all earthly life, as well as the life forms themselves. The lithosphere is the soil and bedrock that cover Earth’s surface. This scene shows Wonder Lake and Mt. McKinley (Denali) in Denali National Park, Alaska.

The gaseous envelope of air that surrounds Earth is the atmosphere (atmo is Greek for “air”). It contains the complex mixture of gases needed to sustain life. Most of the atmosphere is close to Earth’s surface, being densest at sea level and rapidly thinning with increased altitude. It is a very dynamic sphere, kept in almost constant motion by solar energy and Earth’s rotation. The hydrosphere (hydro is Greek for “water”) comprises water in all its forms. The oceans contain the vast majority of the water found on Earth and are the moisture source for most precipitation. A subcomponent of the hydrosphere is known as the cryosphere (cry comes from the Greek word for “cold”)—water frozen as snow and ice. The biosphere (bio is Greek for “life”) encompasses all the parts of Earth where living organisms can exist; in its broadest and loosest sense, the term also includes the vast variety of earthly life forms (properly referred to as biota). These “spheres” are not discrete and separated entities but rather are considerably interconnected. This intermingling is readily apparent when considering an ocean—a body that is clearly a major component of the

Earth’s environmental spheres operate and interact through a complex of Earth systems. By “system” we mean a collection of things and processes connected together and operating as a whole. In the human realm, for example, we talk of a global “financial system” that encompasses the exchange of money between institutions and individuals, or of a “transportation system” that involves the movement of people and commodities. In the natural world, systems entail the interconnected flows and storage of energy and matter. Closed Systems: Some systems are effectively selfcontained and therefore isolated from influences outside that system—and so are called closed systems. It is rare to find closed systems in nature. Earth as a whole is essentially a closed system with regard to matter—currently there is no significant increase or decrease in the amount of matter (the “stuff”) of Earth, although relatively small but measurable amounts of meteoric debris arrives from space, and tiny amounts of gas are lost to space from the atmosphere. Energy, on the other hand, does enter and exit the Earth system constantly. Open Systems:Most Earth systems are open systems— both energy and matter are exchanged across the system boundary. Matter and energy that enter the system are called inputs, and losses from the system to its surroundings are called outputs. For example, as we’ll see in Chapter 19, a glacier behaves as an open system (Figure1-6). The material inputs to a glacier include water in the form of snow and ice, along with rocks and other materials picked up by the moving ice; the material outputs of a glacier include the meltwater and water vapor lost to the atmosphere, as well as the rock transported and eventually deposited by the ice. The most obvious energy input into a glacial system is solar radiation that melts the ice by warming the surrounding air and by direct absorption into the ice itself. But also at work are less obvious exchanges of energy that involve latent heat—energy stored by water during melting and evaporation, and released during freezing and condensation (latent heat is discussed in detail in Chapter 6). Equilibrium:When inputs and outputs are in balance over time, the conditions within a system remain the same; such a system can be described as being in equilibrium. For

CHAPTER 1Introduction to Earth9

Material Input: Snow and ice

Material Input: Rock and debris

Energy Input: Solar radiation

Energy Output: Latent heat exchanged between ice, liquid water, and water vapor

Inpu

ts

Dire

ction

G Sysltacier em

of ic

e mo

Outp

vem

uts

ent

Glacier ice

Material Output: Meltwater and water vapor

Material Output: Rock and debris

▲Figure 1-6 A simplified view of a glacier as an open system. The primary material inputs of a

glacier include snow, ice, and rock, whereas its outputs include meltwater, water vapor, and rock transported by the flowing ice. Theenergy interchange includes incoming solar radiation and the exchange of latent heat between ice, liquid water, and water vapor.

instance, a glacier will remain the same size over many years if its inputs of snow and ice are balanced by the loss of an equivalent amount of ice through melting. If, however, the balance between inputs and outputs changes, equilibrium will be disrupted—increasing snowfall for several years, for example, can cause a glacier to grow until a new equilibrium size is reached. Interconnected Systems:In physical geography we study the myriad of interconnections between Earth’s systems and subsystems. Continuing with our example of a glacier: The system of an individual glacier is interconnected with many other Earth systems, including Earth’s solar radiation budget (discussed in Chapter 4), wind and pressure patterns (discussed in Chapter 5), and the hydrologic cycle (discussed in Chapter 6)—if inputs or outputs in those systems change, a glacier may also change. For instance, if air temperature increases through a change in Earth’s solar radiation budget, both the amount of water vapor available to precipitate as snow and the rate of melting of that snow, may change, causing an adjustment in the size of the glacier. Learning Check 1-5

What does it mean when we say a system is in equilibrium?

Feedback Loops:Some systems produce outputs that “feedback” into that system, reinforcing change. As we’ll see in Chapter 8, over the last few decades increasing

temperatures in the Arctic have reduced the amount of highly reflective, summer sea ice. As the area of sea ice has diminished, the darker, less reflective ocean has absorbed more solar radiation, contributing to the temperature increase—which in turn has reduced the amount of sea ice even more, further reducing reflectance and increasing absorption. Were Arctic temperatures to decrease, an expanding cover of reflective sea ice would reduce absorption of solar radiation and so reinforce a cooling trend. These are examples of positive feedback loops—change within a system continuing in one direction. Conversely, negative feedback loops tend to inhibit a system from changing—in this case increasing a system input tends to decrease further change, keeping the system in equilibrium. For example, an increase in air temperature may increase the amount of water vapor in the air; this greater amount of water vapor may in turn condense and increase the cloud cover—which can reflect incoming solar radiation and so prevent a further temperature increase. Although systems may resist change through negative feedback loops, at some point a system may reach a tipping point or threshold beyond which the system becomes unstable and changes abruptly until it reaches a new equilibrium. For instance, as we’ll see in Chapter 9, it is possible that the increasing freshwater runoff from melting glaciers in the Arctic could disrupt the energy transfer of the slow, deep ocean thermohaline circulation in the Atlantic Ocean, triggering a sudden change in climate.

10Physical Geography: A Landscape Appreciation

The preceding examples are not intended to confuse you, but rather to illustrate the great complexity of Earth’s interconnected systems! Because of this complexity, in this book we often first describe one process or Earth system in isolation before presenting its interconnections with other systems.

Arms

Learning Check 1-6

What is the difference between a positive feedback loop and a negative feedback loop?

EARTH AND THE SOLAR SYSTEM Earth is part of a larger solar system—an open system with which Earth interacts. Earth is an extensive rotating mass of mostly solid material that orbits the enormous ball of superheated gases we call the Sun. The geographer’s concern with spatial relationships properly begins with the relative location of this “spaceship Earth” in the universe.

Galactic Bulge

Sun

Animation Solar System Formation

The Solar System Earth is one of eight planets of our solar system, which also contains more than 160 natural satellites or “moons” revolving around the planets, an uncertain number of smaller dwarf planets such as Pluto, scores of comets (bodies composed of frozen liquid and gases together with small pieces of rock and metallic minerals), more than 500,000 asteroids (small, rocky, and sometimes icy objects, mostly less than a few kilometers in diameter), and millions of meteoroids (most of them the size of sand grains). The medium-massed star we call the Sun is the central body of the solar system and makes up more than 99.8 percent of its total mass. The solar system is part of the Milky Way Galaxy, which consists of at least 200,000,000,000 stars arranged in a disk-shaped bared-spiral that is about 100,000 light-years in diameter (1 light-year equals about 9.5 trillion kilometers—the distance a beam of light travels over a period of one year) and 10,000 light-years thick at the center (Figure 1-7). The Milky Way Galaxy is only one of hundreds of billions of galaxies in the universe. To begin to develop an understanding for astronomical distances, we might consider a reduced-scale model of the universe: if the distance between Earth and the Sun, which is about 150,000,000 kilometers (93,000,000 miles), is taken to be 2.5 centimeters (1 inch), then the distance from Earth to the nearest star would be 7.2 kilometers (4.5 miles), and the distance from Earth to the next similar-sized galaxy beyond the Milky Way would be about 240,000 kilometers (150,000 miles)! Origins:The origin of Earth, and indeed of the universe, is incompletely understood. It is generally accepted that the universe began with a cosmic event called the big bang. The most

100,000 light-years ▲Figure 1-7 The structure of the Milky Way Galaxy showing the

approximate location of our Sun on one of the spiral arms.

widely held view is that the big bang took place some 13.7 billion years ago—similar to the age of the oldest known stars. The big bang began in a fraction of a second as an infinitely dense and infinitesimally small bundle of energy containing all of space and time started to expand away in all directions at extraordinary speeds, pushing out the fabric of space and filling the universe with the energy and matter we see today. Our solar system originated between 4.5 and 5 billion years ago when a nebula—a huge, cold, diffuse cloud of gas and dust—began to contract inward, owing to its own gravitational collapse, forming a hot, dense protostar (Figure 1-8). This hot center—our Sun—was surrounded by a cold, revolving disk of gas and dust that eventually condensed and coalesced to form the planets. All of the planets revolve around the Sun in elliptical orbits, with the Sun located at one focus (looking “down” on the solar system from a vantage point high above the North Pole of Earth, the planets appear to orbit in a counterclockwise direction around the Sun). All the planetary orbits are in nearly the same plane (Figure 1-9), perhaps revealing their relationship to the original spinning direction of the nebular disk. The Sun rotates on its axis from west to east. Moreover, most of the planets rotate from west to east on their own axes (Uranus rotates “sideways” with its rotational axis almost parallel to its orbital plane; Venus rotates from east to west). The planets revolve more slowly and generally have a lower temperature as their distance from the Sun increases. The Planets: The four inner terrestrial planets— Mercury, Venus, Earth, and Mars—are generally smaller, denser, and less oblate (more nearly spherical), and they rotate more slowly on their axes than the four outer

CHAPTER 1Introduction to Earth11

1

2

3

4

By contrast, the four Jovian planets tend to be much larger, more massive (although they are less dense), and much more oblate (less perfectly spherical) because they rotate more rapidly. The Jovian planets are mostly composed of elements such as hydrogen and helium—liquid near the surface, but frozen toward the interior—as well as ices of compounds such as methane and ammonia. The Jovian planets generally have atmospheres that are dense, turbulent, and relatively deep. It was long thought that tiny Pluto was the ninth and outermost planet in the solar system. In recent years, however, astronomers have discovered other icy bodies, such as distant Eris, Makemake, and Haumea that are similar to Pluto and orbiting the Sun beyond Neptune in what is referred to as the Kuiper Belt or trans-Neptunian region. In June 2008 the International Astronomical Union reclassified Pluto as a special type of dwarf planet known as a plutoid. Some astronomers speculate that there may be several dozen yet-to-be-discovered plutoids and other dwarf planets in the outer reaches of the solar system. Learning Check 1-7

5

Contrast the characteristics of the terrestrial and Jovian planets in our solar system.

The Size and Shape of Earth

begins to contract inward. (2) Cloud flattens into nebular disk as it spins faster around a central axis. (3) Particles in the outer parts of the disk collide with each other to form protoplanets. (4) Protoplanets coalesce into planets and settle into orbits around the hot center. (5) The final product: a central Sun surrounded by eight orbiting planets (solar system not shown in correct scale). The original nebular disk was much larger than our final solar system.

Is Earth large or small? The answer to this question depends on one’s frame of reference. If the frame of reference is the universe, Earth is almost infinitely small. The diameter of our planet is only about 13,000 kilometers (7900 miles), a tiny distance at the scale of the universe—for instance, the Moon is 385,000 kilometers (239,000 miles) from Earth, the Sun is 150,000,000 kilometers (93,000,000 miles) away, and the nearest star is 40,000,000,000,000 kilometers (25,000,000,000,000 miles) distant.

Jovian planets—Jupiter, Saturn, Uranus, and Neptune. Also, the inner planets are composed principally of mineral matter and, except for airless Mercury, have diverse but relatively shallow atmospheres.

The Size of Earth: In a human frame of reference, however, Earth is impressive in size. Its surface varies in elevation from the highest mountain peak, Mount Everest, at 8850 meters (29,035 feet) above sea level, to the deepest oceanic trench, the Mariana Trench of the Pacific Ocean, at

▲Figure 1-8 The birth of the solar system. (1) Diffuse gas cloud, or nebula,

Uranus Mercury Asteroid Belt

Mars

Venus

Jupiter

Earth Saturn

Neptune

▲Figure 1-9 The solar system (not drawn to correct scale). The Sun is not exactly at the center of the solar system—the planets revolve around the

Sun in elliptical orbits. The Kuiper Belt, which includes dwarf planets such as Pluto, begins beyond Neptune.

12Physical Geography: A Landscape Appreciation

8850 meters (29,035 ft.) Sea level

Total relief

19,883 meters (65,233 ft.)

Mt. Everest

Sea level

Mariana Trench 11,033 meters (36,198 ft.)

+ +

12,756,274 meters (about 12,756 km or 7,926 mi.)

Equator

trigonometrically. He determined the angle of the noon Sun rays at Alexandria and at the city of Syene, 960 kilometers (600 miles) away. From these angular and linear distances he was able to estimate an Earth circumference of almost 43,000 kilometers (26,700 miles) which is reasonably close to the actual figure of 40,000 kilometers (24,900miles). The Shape of Earth:Earth is almost, but not quite, spherical. The cross section revealed by a cut through the equator would be circular, but a similar cut from pole to pole would be an ellipse rather than a circle (Figure 1-11). Any rotating body has a tendency to bulge around its equator and flatten at the polar ends of its rotational axis. Although the rocks of Earth may seem quite rigid and immovable to us, they are sufficiently pliable to allow Earth to develop a bulge around its middle. The slightly flattened polar diameter of Earth is 12,714 kilometers (7900 miles), whereas the slightly bulging equatorial diameter is 12,756 kilometers (7926 miles), a difference of only about 0.3 percent. Thus, our planet is properly described as an oblate spheroid rather than a true sphere. However, because this variation from true sphericity is exceedingly small, in most cases in this book we will treat Earth as if it were a perfect sphere. Learning Check 1-8 What are Earth’s highest and lowest points, and what is the approximate elevation difference between them?

▲Figure 1-10 Earth is large relative to the size of its surface features.

Earth’s maximum relief (the difference in elevation between the highest and lowest points) is 19,883 meters (65,233 feet) or about 20 kilometers (12 miles) from the top of Mount Everest to the bottom of the Mariana Trench in the Pacific Ocean.

North Pole

12,714 km

11,033 meters (36,198 feet) below sea level, a total difference in elevation of 19,883 meters (65,233 feet). Although prominent on a human scale of perception, this difference is minor on a planetary scale, as Figure1-10 illustrates. If Earth were the size of a basketball, Mount Everest would be an imperceptible pimple no greater than 0.17 millimeter (about 7 thousandths of an inch) high. Similarly, the Mariana Trench would be a tiny crease only 0.21 millimeter (about 8 thousandths of an inch) deep— this represents a depression smaller than the thickness of a sheet of paper. Our perception of the relative size of topographic irregularities on Earth is often distorted by three-dimensional wall maps and globes that emphasize such landforms. To portray any noticeable appearance of topographic variation, the vertical distances on such maps are usually exaggerated 8 to 20 times their actual proportional dimensions—as are many diagrams used in this book. Further, many diagrams illustrating features of the atmosphere also exaggerate relative sizes to convey important concepts. More than 2600 years ago Greek scholars correctly reasoned Earth to have a spherical shape. About 2200 years ago, Eratosthenes, the director of the Greek library at Alexandria, calculated the circumference of Earth

North Pole

(a) A diameter through the poles North Pole

Resulting cross section South Pole

Equ

ator

12,

756

km

Equator

Resulting cross section (b) A diameter through the equator ▲Figure 1-11 Earth is not quite a perfect sphere. Its surface flattens

slightly at the North Pole and the South Pole and bulges out slightly around the equator. Thus, a cross section through the poles, shown in (a), has a diameter slightly less than the diameter of a cross section through the equator, shown in (b).

CHAPTER 1Introduction to Earth13 North Pole

THE GEOGRAPHIC GRID— LATITUDE AND LONGITUDE Any understanding of the distribution of geographic features over Earth’s surface requires some system of accurate location. The simplest technique for achieving this is a grid system consisting of two sets of lines that intersect at right angles, allowing the location of any point on the surface to be described by the appropriate intersection, as shown in Figure 1-12. Such a rectangular grid system has been reconfigured for Earth’s spherical surface. If our planet were a nonrotating body, the problem of describing surface locations would be more difficult than it is: imagine trying to describe the location of a particular point on a perfectly round, perfectly clean Ping-Pong ball. Because Earth does rotate, we can use its rotation axis as a starting point to describe locations. Earth’s rotation axis is an imaginary line passing through Earth that connects the points on the surface called the North Pole and the South Pole (Figure 1-13). Further, if we visualize an imaginary plane passing through Earth halfway between the poles and perpendicular to the axis of rotation, we have another valuable reference feature: the plane of the equator. Where this plane intersects Earth’s surface is the imaginary midline of Earth, called simply the equator. We use the North Pole, South Pole, rotational axis, and equatorial plane as natural reference features for measuring and describing locations on Earth’s surface. Great Circles:Any plane that is passed through the center of a sphere bisects that sphere (divides it into two equal halves) and creates what is called a great circle where

Equator

Equatorial Plane

South Pole ▲Figure 1-13 Earth spins around its rotation axis, an imaginary line

that passes through the North Pole and the South Pole. An imaginary plane bisecting Earth midway between the two poles defines the equator.

it intersects the surface of the sphere (Figure 1-14a). The equator is such a great circle. Planes passing through any other part of the sphere produce what are called small circles where they intersect the surface (Figure 1-14b). Great circles have two properties of special interest for us: 1. A great circle is the largest circle that can be drawn on a sphere; it represents the circumference of that sphere and divides its surface into two equal halves or hemispheres. As we’ll see later in this chapter, the

North Pole

A

B

C

D

E

1

Equator

2

3

Equator

X (a) Forming great circles

Y

4

Equator

5

Equator

(b) Forming small circles ▲Figure 1-14 Comparison of great and small circles. (a) A great circle

▲Figure 1-12 An example of a grid system. The location of point X can

be described as 2B or as B2; the location of Y is 3D or D3.

results from the intersection of Earth’s surface with any plane that passes through Earth’s center. (b) A small circle results from the intersection of Earth’s surface with any plane that does not pass through Earth’s center.

14Physical Geography: A Landscape Appreciation

dividing line between the daytime and nighttime halves of Earth is a great circle. 2. A path between two points along the arc of a great circle is always the shortest route between those points. Such routes on Earth are known as great circle routes (great circle routes will be discussed in more detail in Chapter 2).

North Pole (90°N)

70°N 60°N 50°N 40°N

The geographic grid used as the locational system for Earth is based on the principles just discussed. Furthermore, the system is closely linked with the various positions assumed by Earth in its orbit around the Sun. The grid system of Earth is referred to as a graticule and consists of lines of latitude and longitude.

30°N 20°N 10°N 0° 10°S 20°S 30°S

Learning Check 1-9

What is a great circle? Provide one example of a great circle.

▲Figure 1-16 Lines of latitude indicate north-south location. They are

Latitude

called parallels because they are always parallel to each other.

Latitude is a description of location expressed as an angle north or south of the equator. As shown in Figure 1-15, we can project a line from any location on Earth’s surface to the center of Earth. The angle between this line and the equatorial plane is the latitude of that location. Latitude is expressed in degrees, minutes, and seconds. There are 360 degrees (°) in a circle, 60 minutes (') in one degree, and 60 seconds (˝ ) in one minute. With the advent of GPS navigation (discussed in Chapter 2), it is increasingly common to see latitude and longitude designated using decimal notation, for example, 38°22´47˝ N can be written 38°22.78´ N or even 38.3797° N.

North Pole 90° N

Kuji 40° N 30° N

40° N

20° N

E

qu

at or

80°N

10° N 20° S

0° 10° S

Bowen

20° S

South Pole 90° S

Latitude varies from 0° at the equator to 90° north at the North Pole and 90° south at the South Pole. Any position north of the equator is north latitude, and any position south of the equator is south latitude (the equator itself is simply referred to as having a latitude of 0°). A line connecting all points of the same latitude is called a parallel—because it is parallel to all other lines of latitude (Figure 1-16). The equator is the parallel of 0° latitude, and it, alone of all parallels, constitutes a great circle. All other parallels are small circles—all aligned in true east–west directions on Earth’s surface. Because latitude is expressed as an angle, it can be infinitely subdivided—parallels can be constructed for every degree of latitude, or even for fractions of a degree of latitude. Although it is possible to either construct or visualize an unlimited number of parallels, seven latitudes are of particular significance in a general study of Earth (Figure 1-17): 1. 2. 3. 4. 5. 6. 7.

Equator, 0° Tropic of Cancer, 23.5° N Tropic of Capricorn, 23.5° S (Figure 1-18) Arctic Circle, 66.5° N Antarctic Circle, 66.5° S North Pole, 90° N South Pole, 90° S

The North Pole and South Pole are of course points rather than lines, but can be thought of as infinitely small parallels. The significance of these seven parallels will be explained later in this chapter when we discuss the seasons.

▲Figure 1-15 Measuring latitude. An imaginary line from Kuji, Japan,

to Earth’s center makes an angle of 40° with the equator. Therefore, Kuji's latitude is 40° N. An imaginary line from Bowen, Australia, to Earth’s center makes an angle of 20°, giving this city a latitude of 20° S.

Learning Check 1-10 called parallels?

Why are lines of latitude

CHAPTER 1Introduction to Earth15

Descriptive Zones of Latitude:Regions on Earth are sometimes described as falling within general bands or zones of latitude. The following common terms associated with latitude are used throughout this book (note that there is some overlap between several of these terms):

North Pole 90°N Arc

tic

Cir cle 66.

5°N

Tro pi

co

fC

S

anc

er

Equ

ato

S

r

S S

23.

Tro pi

co

5°N

fC

S S

apr

ico

rn 0°

Ant

23.

5°S

arc

tic

Cir cle

66.

5°S

South Pole 90°S ▲Figure 1-17 Seven important parallels. As we will see when we discuss

the seasons, these latitudes represent special locations where rays from the Sun strike Earth’s surface on certain days of the year.

S

Low latitude—generally between the equator and 30° N and S Midlatitude—between about 30° and 60° N and S High latitude—latitudes greater than about 60° N and S Equatorial—within a few degrees of the equator Tropical—within the tropics (between 23.5° N and 23.5° S) Subtropical—slightly poleward of the tropics, generally around 25–30° N and S Polar—within a few degrees of the North or South Pole

Nautical Miles:Each degree of latitude on the surface of Earth covers a north–south distance of about 111 kilometers (69 miles). The distance varies slightly with latitude because of the flattening of Earth at the poles. The distance measurement of a nautical mile—and the description of speed known as a knot (one nautical mile per hour)—is defined by the distance covered by one minute of latitude (1´), the equivalent of about 1.15 statute (“ordinary”) miles or about 1.85 kilometers.

Longitude

10°W

30°W 20°W

80°E 70°E 60°E

40°E

30°E

20°E

Alice Springs

10°E

Tr o p i c o f C a p r i c o r n

50°E

50°W 40°W

Latitude comprises the north–south component of Earth’s grid system. The other half is longitude—an angular description of east–west location, also measured in degrees, minutes, and seconds. Longitude is represented by imaginary lines extending from pole to pole and crossing all parallels at right angles. These lines, called meridians, are not parallel to one another except where they cross the equator. Any pair of meridians is farthest apart at the equator, becoming increasingly close together northward and southward and finally converging at the poles (Figure 1-19).

AUSTRALIA

▲Figure 1-18 The Tropic of Capricorn; like all other parallels of latitude,

is an imaginary line. As a significant parallel, however, its location is often commemorated by a sign. This scene is near Alice Springs in the center of Australia.

▲Figure 1-19 Lines of longitude, or meridians, indicate east–west

location and all converge at the poles.

16Physical Geography: A Landscape Appreciation North Pole

Freetown

Prime Meridian

Greenwich

13°W

Establishing the Prime Meridian: The equator is a natural baseline from which to measure latitude, but no such natural reference line exists for longitude. Consequently, for most of recorded history, there was no accepted longitudinal baseline; each country would select its own “prime meridian” as the reference line for east–west measurement. Thus, the French measured from the meridian of Paris, the Italians from the meridian of Rome, and so forth. At least 13 prime meridians were in use in the 1880s. Not until the late 1800s was standardization finally achieved. United States and Canadian railway executives adopted a standard time system for all North American railroads in 1883, and the following year an international conference was convened in Washington, D.C., to achieve the same goal on a global scale and to agree upon a single prime meridian. After weeks of debate, the delegates chose the meridian passing through the Royal Observatory at Greenwich, England, just east of London, as the prime meridian for all longitudinal measurement (Figure 1-20). The principal argument for adopting the Greenwich meridian as the prime meridian was a practical one: more than two-thirds of the world’s shipping lines already used the Greenwich meridian as a navigational base. Thus, an imaginary north–south plane passing through Greenwich and through Earth’s axis of rotation represents the plane of the prime meridian. The angle between this plane and a plane passed through any other point and the

0° or t a Equ

South Pole

13° ▲Figure 1-21 The meridians that mark longitude are defined by

10°

UNITED KINGDO M

intersecting imaginary planes passing through the poles. Shown here are the planes for the prime meridian through Greenwich, England, and the meridian through Freetown, Sierra Leone, at 13° west longitude.

P rim e M erid ian

I R E LAND

55°

Greenwich 50°

▲Figure 1-20 The prime meridian of the world, longitude 0°0´0˝ at Greenwich, England, which is about 8 km (5 miles) from the heart of London.

axis of Earth is a measure of longitude. For example, the angle between the Greenwich plane and a plane passing through the center of the city of Freetown (in the western African country of Sierra Leone) is 13 degrees, 15 minutes, and 12 seconds. Because the angle is formed west of the prime meridian, the longitude of Freetown is written 13°15´12˝ W (Figure 1-21). Measuring Longitude:Longitude is measured both east and west of the prime meridian to a maximum of 180° in each direction. Exactly halfway around the globe from the prime meridian, in the middle of the Pacific Ocean, is the 180° meridian (Figure 1-22). All places on Earth, then, have a location that is either east longitude or west longitude, except for points exactly on the prime meridian (described simply as 0° longitude) or exactly on the 180th meridian (described as 180° longitude). The distance between any two meridians varies predictably. At the equator, the surface length of one degree of longitude is about the same as that of one degree of latitude. However, because meridians converge at the poles, the distance covered by one degree of longitude decreases poleward (Figure 1-23), diminishing to zero at the poles where all meridians meet at a point.

CHAPTER 1Introduction to Earth17 0° 30°E

30°W

Prime Meridian

60°E

60°W

North Pole

90°E

90°W

detailed latitude and longitude data. For example, at the 1964 World’s Fair in New York City, a time capsule (a container filled with records and memorabilia of contemporary life) was buried. For reference purposes, the U.S. Coast and Geodetic Survey determined that the capsule was located at 40°28´34.089˝ north latitude and 73°43´16.412˝ west longitude. At some time in the future, if a hole were to be dug at the spot indicated by those coordinates, it would be within 15 centimeters (6 inches) of the capsule. Learning Check 1-11

Are locations in North America described by east longitude or west longitude? 120°E

120°W 180° Meridian 150°E

EARTH–SUN RELATIONS AND THE SEASONS

150°W 180°

▲Figure 1-22 A polar view of meridians radiating from the North Pole.

Think of each line as the top edge of an imaginary plane passing through both poles. All the planes are perpendicular to the plane of the page.

Locating Points on the Geographic Grid

Longitude 1° = 0 km

Latitude 1° = 111 km

Latitude 1° = 112 km

The network of intersecting parallels and meridians creates a geographic grid over the entire surface of Earth (see Figure 1-23). The location of any place on Earth’s surface can be described with great precision by reference to

Nearly all life on Earth depends on solar Animation energy; therefore, the relationship between Earth–Sun Relations Earth and the Sun is of vital importance. Because of the perpetual motions of Earth, this relationship does not remain the same throughout the year. We begin with a description of Earth movements and the relationship of Earth’s axis to the Sun, and then we offer an explanation of the change of seasons.

North Pole (90°N)

Longitude 1° = 56 km

80°N 70°N

10°N

Longitude 1° = 96 km

0° 10°S 20°S 30°S

Latitude 1° = 111 km

10°W

20°N

40°E

20°W

30°N

80°E 70°E 60°E 50°E

40°N

30°E

50°W 40°W 30°W

50°N

Latitude 1° = 111 km

60°N

◀Figure 1-23 The complete grid system of latitude and

Longitude 1° = 111 km

longitude—the graticule. Because the meridians converge at the poles, the distance of 1° of longitude is greatest at the equator and diminishes to zero at the poles, whereas the distance of 1° of latitude varies only slightly (due to the slight flattening of Earth at the poles).

18Physical Geography: A Landscape Appreciation

Earth Movements Two basic Earth movements—its daily rotation on its axis and its annual revolution around the Sun—along with the inclination and “polarity” of Earth’s rotation axis, combine to change Earth’s orientation to the Sun—and therefore produce the change of seasons. Earth’s Rotation on Its Axis:Earth rotates from west to east on its axis (Figure 1-24), a complete rotation requiring 24 hours (from the vantage point of looking down at the North Pole from space, Earth is rotating in a counterclockwise direction). The Sun, the Moon, and the stars appear to rise in the east and set in the west—this is, of course, an illusion created by the steady eastward spin of Earth. Rotation causes all parts of Earth’s surface except the poles to move in a circle around Earth’s axis. Although the speed of rotation varies by latitude (see Figure 1-24), it is constant at any given place on Earth and so we experience no sense of motion. This is the same reason that we have little sense of motion on a smooth jet airplane flight at cruising speed—only when speed changes, such as during takeoff and landing, does motion become apparent. Rotation has several important effects on the physical characteristics of Earth’s surface: 1. Earth’s constant rotation causes an apparent deflection in the paths of both wind and ocean currents—to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This phenomenon is called the Coriolis effect and is discussed in detail in Chapter3.

North Pole Rotation axis

North Pole: 0 kph (0 mph) 60°N: 840 kph (520 mph) 30°N: 1450 kph (900 mph)

Equator: 1670 kph (1040 mph)

W es

t East

South Pole ▲Figure 1-24 Earth rotates from west to east. Looking down at the North Pole from above, Earth appears to rotate in a counterclockwise direction. The speed of Earth’s rotation is constant but it varies by latitude, being greatest at the equator, and effectively diminishing to zero at the poles. The speed of rotation at different latitudes is shown in kilometers per hour (kph) and miles per hour (mph).

2. The rotation of Earth brings any point on the surfacethrough the increasing and then decreasing gravitational pull of the Moon and the Sun. Although the land areas of Earth are too rigid to be significantly moved by these oscillating gravitational attractions, oceanic waters move onshore and then recede in a rhythmic pattern of tides, discussed further in Chapter 9. 3. Undoubtedly the most important effect of earthly rotation is the diurnal (daily) alternation of daylight and darkness, as portions of Earth’s surface are turned first toward and then away from the Sun. This variation in exposure to sunlight greatly influences local temperature, humidity, and wind movements. Except for the organisms that live either in caves or in the ocean deeps, all forms of life have adapted to this sequential pattern of daylight and darkness. We human beings fare poorly when our circadian (24-hour cycle) rhythms are misaligned as the result of high-speed air travel that significantly interrupts the normal sequence of daylight and darkness. We are left with a sense of fatigue known as “jet lag,” which can include unpleasant changes in our usual patterns of appetite and sleep. Earth’s Revolution around the Sun:Another significant Earth motion is its revolution or orbit around the Sun. Each revolution takes 365 days, 5 hours, 48 minutes, and 46 seconds, or 365.242199 days. This is known officially as the tropical year and for practical purposes is usually simplified to 365.25 days. (Astronomers define the year in other ways as well, but the duration is very close to that of the tropical year and need not concern us here.) The path followed by Earth in its journey around the Sun is not a true circle but an ellipse (Figure 1-25). Because of this elliptical orbit, the Earth–Sun distance is not constant; rather, it varies from approximately 147,100,000 kilometers (91,400,000 miles) at the closest or perihelion position (peri is from the Greek and means “around” and helios means “Sun”) on about January 3, to approximately 152,100,000 kilometers (94,500,000 miles) at the farthest or aphelion position (ap is from the Greek and means “away from”) on about July 4. The average Earth–Sun distance is defined as one astronomical unit (1 AU) and is about 149,597,871 kilometers (92,960,117 miles). Earth is 3.3 percent closer to the Sun during the Northern Hemisphere winter than during the Northern Hemisphere summer, an indication that variations in the distance between Earth and the Sun do not cause the change of seasons; instead, two additional factors in the relationship of Earth to the Sun—inclination and polarity—work together with rotation and revolution to produce the change of seasons. Learning Check 1-12

Distinguish between Earth’s rotation and its revolution.

Inclination of Earth’s Axis: The imaginary plane defined by the orbital path of Earth around the Sun is called the plane of the ecliptic (see Figure 1-25). However,

CHAPTER 1Introduction to Earth19

Eq

uat o

r

23.5°

Ellipse foci

Eq ua

tor

n Aphelio km 0 0 ,0 0 0 152,1 iles) m 0 0 ,0 (94,500

23.5° on Periheli 0 km 0 ,0 0 0 147,1 miles) 0 0 ,0 (91,400

Eq

ua

tor

January 3rd

Sun

July 4th Eq

uat o

h’s Eart

l ita orb

th pa

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▲Figure 1-25 The plane of the ecliptic is the orbital plane of Earth. Because Earth’s rotation axis is tilted, the plane of the ecliptic and the equatorial

plane do not coincide. The path Earth follows in its revolution around the Sun is an ellipse with the Sun at one focus. Earth reaches perihelion (its closest point to the Sun) on about January 3rd and aphelion (its farthest point from the Sun) on about July 4th. (In this diagram the elliptical shape of Earth’s orbit is greatly exaggerated.)

Earth’s rotation axis is not perpendicular to the plane of the ecliptic. Rather, the axis is tilted about 23.5° from the perpendicular (Figure 1-26) and maintains this tilt throughout the year. This tilt is referred to as the inclination of Earth's axis.

Learning Check 1-13

Does the North Pole lean toward the Sun throughout the year? If not, how does the North Pole’s orientation change during the year?

Perpendicular to Plane of Ecliptic

Equ

66.5°

ato

r

23.5°

tati

on

axi

s

Plane of Ecliptic

Ro

Polarity of Earth’s Axis:Not only is Earth’s rotation axis inclined relative to its orbital path, no matter where Earth is in its orbit around the Sun the axis always points in the same direction relative to the stars—toward the North Star, Polaris (Figure 1-27). In other words, at any time during the year, Earth’s rotation axis is parallel to its orientation at all other times. This characteristic is called the polarity of Earth’s axis (or parallelism). The combined effects of rotation, revolution, inclination, and polarity result in the seasonal patterns experienced on Earth. Notice in Figure 1-27 that at one point in Earth’s orbit, around June 21, the North Pole is oriented most directly toward the Sun, whereas six months later, around December 21, the North Pole is oriented most directly away from the Sun—this is the most fundamental feature of the annual march of the seasons.

North 23.5° Pole

South Pole ▲Figure 1-26 Earth’s rotation axis is inclined 23.5° from a line

perpendicular to the plane of the ecliptic.

The Annual March of the Seasons During a year, the changing relationship of Earth to the Sun results in variations in day length and in the angle at which the Sun’s rays strike the surface of Earth. These changes are

20Physical Geography: A Landscape Appreciation

March 20 Equinox

rth Ea

it orb

North Pole

Equator

Arctic Circle Arctic Circle

Sun

June 21 Solstice

Circle of Illumination

December 21 Solstice

Circle of Illumination

September 22 Equinox

Plane of the ecliptic

▲Figure 1-27 A “top view” of the march of the seasons. Earth’s rotational axis maintains polarity (points in the same direction) throughout the year, so on the June solstice the North Pole leans most directly toward the Sun, whereas on the December solstice the North Pole leans most directly away from the Sun (the dates shown are approximate). One-half of Earth is illuminated at all times during the year. The line between the two halves is called the circle of illumination.

most obvious in the mid- and high latitudes, but important variations take place within the tropics as well. As we discuss the annual march of the seasons, we will pay special attention to three conditions: 1. The latitude receiving the vertical rays of the Sun (rays striking the surface at a right angle), also referred to as the subsolar point or the declination of the Sun. 2. The solar altitude (the height of the Sun above the horizon) at different latitudes. 3. The length of day (number of daylight hours) at different latitudes. Initially, we emphasize the conditions on four special days of the year: The March equinox, the June solstice, the September equinox, and the December solstice (Figure 1-28). As we describe the change of seasons, the significance of the “seven important parallels” discussed earlier in this chapter will become clear. We begin with the June solstice. June Solstice: On the June solstice, which occurs on or about June 21 (the exact date varies slightly from year to year), the Earth reaches the position in its orbit where the North Pole is oriented most directly toward the Sun. On this day, the vertical rays of the Sun at noon are

striking the Tropic of Cancer, 23.5° north of the equator (Figure1-28b). Were you at the Tropic of Cancer on this day, the Sun would be directly overhead in the sky at noon (in other words, the solar altitude would be 90°). The Tropic of Cancer marks the northernmost location reached by the vertical rays of the Sun during the year. The dividing line between the daylight half of Earth and nighttime half of Earth is a great circle called the circle of illumination. On the June solstice, the circle of illumination bisects (“cuts in half”) the equator (Figure 1-28b), so on this day the equator receives equal day and night—12hours of daylight and 12 hours of darkness. However, as we move north of the equator, the portion of each parallel in daylight increases—in other words, as we move north of the equator, day length increases. Conversely, day length decreases as we move south of the equator. Notice in Figure 1-28b that on the June solstice, the circle of illumination reaches 23.5° beyond the North Pole to a latitude of 66.5° N. As Earth rotates, all locations north of 66.5° remain continuously in daylight and so on this day experience 24 hours of daylight. By contrast, all points south of 66.5° S are always outside the circle of illumination and so have 24 continuous hours of darkness. These special parallels defining the equatorward limit of 24 hours of light

CHAPTER 1Introduction to Earth21 March Equinox March 20 (a) Oblique view

December Solstice December 21

June Solstice June 21 Sun

North Pole

Arc

tic

Tro pi

co

Cir cle

fC

anc

er

Equ

ato

Tro pi

co

Ant

arc

fC

South Pole

tic

apr

r

North Pole

Arc

tic

September Equinox September 22

Tro pi

co

North Pole

ico

rn Arct

Cir cle

fC

anc

er

Equ

ato

Vertical ray

Vertical ray

Cir cle

Tro pi

co

Ant

arc

fC

ic Circle

tic

apr

r

ico

rn

Cir cle

South Pole

Circle of illumination

(b) June solstice side view

Tropic of Cancer

Vertical ray

(d) December solstice side view

Equator

Tropic of Capricorn

South Pole

(c) September equinox side view ▲Figure 1-28 (a) The annual march of the seasons showing Earth–Sun relations on the June solstice, September equinox,

December solstice, and March equinox (the dates shown are approximate). The circle of illumination is the dividing line between the daylight and nighttime halves of Earth. (b) On the June solstice the vertical rays of the noon Sun strike 23.5° N latitude. (c) On the March equinox and September equinox, the vertical rays of the noon Sun strike the equator. (d) On the December solstice, the vertical rays of the noon Sun strike 23.5° S latitude.

and dark on the solstice dates are called the polar circles. The northern polar circle, at 66.5° N, is the Arctic Circle; the southern polar circle, at 66.5° S, is the Antarctic Circle. The June solstice is called the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere (what are commonly called the “first day of summer” and the “first day of winter” in their respective hemispheres). Learning Check 1-14

What is the latitude of the vertical rays of the Sun on the June solstice?

September Equinox: Three months after the June solstice, on approximately September 22 (as with solstice dates, this date also varies slightly from year to year), Earth

experiences the September equinox. Notice in Figure 1-28c that the vertical rays of the Sun are striking the equator. Notice also that the circle of illumination just touches both poles, bisecting all other parallels—on this day all locations on Earth experience 12 hours of daylight and 12 hours of darkness (the word “equinox” comes from the Latin, meaning “the time of equal days and equal nights”). At the equator— and only at the equator—every day of the year has virtually 12 hours of daylight and 12 hours of darkness; all other locations have equal day and night only on an equinox. The September equinox is called the autumnal equinox in the Northern Hemisphere and the vernal equinox in the Southern Hemisphere (and what are commonly called the “first day of fall” and the “first day of spring” in their respective hemispheres).

22Physical Geography: A Landscape Appreciation

December Solstice:On the December solstice, which occurs on or about December 21, the Earth reaches the position in its orbit where the North Pole is oriented most directly away from the Sun; the vertical rays of the Sun now strike 23.5° S, the Tropic of Capricorn (Figure 1-28d). Once again, the circle of illumination reaches to the far side of one pole and falls short on the near side of the other pole—areas north of the Arctic Circle are in continuous darkness, whereas areas south of the Antarctic Circle are in daylight for 24 hours. Although the latitude receiving the vertical rays of the Sun has shifted 47° from June 21 to December 21, the relationships between Earth and the Sun on the June solstice and the December solstice are very similar— the conditions in each hemisphere are simply reversed. The December solstice is called the winter solstice in the Northern Hemisphere and the summer solstice in the Southern Hemisphere (what are commonly called the “first day of winter” and the “first day of summer,” respectively). March Equinox:Three months after the December solstice, on approximately March 20, Earth experiences the March equinox. The relationships of Earth and the Sun are virtually identical on the March equinox and the September equinox (Figure 1-28c). The March equinox is called the vernal equinox in the Northern Hemisphere and the autumnal equinox in the Southern Hemisphere (what are commonly called the “first day of spring” and the “first day of fall,” respectively). Table 1-2 summarizes the conditions present during the solstices and equinoxes. Learning Check 1-15 How much does day length at the equator change during the year?

TABLE 1-2

Seasonal Transitions In the preceding discussion of the solstices and equinoxes, we mainly emphasized the conditions on just four special days of the year. It is important to understand the transitions in day length and Sun angle that take place between those days as well. Latitude Receiving the Vertical Rays of the Sun:The vertical rays of the Sun only strike Earth between the Tropic of Cancer and the Tropic of Capricorn. After the March equinox, the vertical rays of the Sun migrate north from the equator, striking the Tropic of Cancer on the June solstice (although latitudes north of the Tropic of Cancer never experience the vertical rays of the Sun, the June solstice marks the day of the year when the Sun is highest in the sky in those latitudes). After the June solstice, the vertical rays migrate south, striking the equator again on the September equinox and finally to their southernmost latitude on the December solstice (the December solstice marks the day of the year when the Sun is lowest in the sky in the Northern Hemisphere). Following the December solstice, the vertical rays migrate northward, reaching the equator once again on the March equinox. The changing latitude of the vertical rays of the Sun during the year is shown graphically on a chart known as the analemma (Figure 1-29). Day Length:Only at the equator is day length constant throughout the year—virtually 12 hours of daylight every day of the year. For all regions in the Northern Hemisphere up to the latitude of the Arctic Circle, after the shortest day of the year on the December solstice, the number of hours

Conditions on Equinoxes and Solstices March Equinox

June Solstice

September Equinox

December Solstice

Latitude of Vertical Rays of Sun

23.5° N

23.5° S

Day length at Equator

12 hours

12 hours

12 hours

12 hours

Day length in midlatitudes of Northern Hemisphere

12 hours

Day length becomes longer with increasing latitude north of equator

12 hours

Day length becomes shorter with increasing latitude north of equator

Day length in midlatitudes of Southern Hemisphere

12 hours

Day length becomes shorter with increasing latitude south of equator

12 hours

Day length becomes longer with increasing latitude south of equator

24 hours of daylight

Nowhere

From Arctic Circle to North Pole

Nowhere

From Antarctic Circle to South Pole

24 hours of darkness

Nowhere

From Antarctic Circle to South Pole

Nowhere

From Arctic Circle to North Pole

Season in Northern Hemisphere

Spring

Summer

Autumn

Winter

Season in Southern Hemisphere

Autumn

Winter

Spring

Summer

CHAPTER 1Introduction to Earth23

Sun fast by 6M

4M

2M

22°

16° 14°

r il Ap

10°

10 5

em be

25

pt

20

30

ch ar

5 10

25

ry

10°

Februa

25 30

15 10

m

ve

30

r

be

18° 10 15 20°

20

5

No

16° 5

Day Length

90° N

24 h

23.5

60° N

18 h 53 min

53.5

30° N

14 h 05 min

83.5

12 h 07 min

66.5

30° S

10 h 12 min

36.5

60° S

05 h 52 min

6.5

90° S

Source: After Robert J. List, Smithsonian Meteorological Tables, 6th rev. ed. Washington, D.C.: Smithsonian Institution, 1963, Table 171.

5

Oc

20

Latitude

10

tob

15

15

er

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20

25

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30

Se

r

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South

20 20 25

10

Day Length at Time of June Solstice

15

5

24°

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M

Declination of Sun

22°

10 20

30 5

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12°

TABLE 1-3

Tropic of Cancer

Au gu st

May

18°

20 15 10 5 30

Sun slow by 6M 8M 10M 12M 14M

4M

30

20°

14°

2M

June 10 20 30

24°

12°

0M

ly Ju

North

16M 14M 12M 10M 8M

ary 25 20 15 Tropic of 10 Capricorn u Jan

20 25 30

December 5

10

15

20

25

30

5

▲Figure 1-29 The analemma shows the latitude of the vertical rays of the

noon Sun (the declination of the Sun) throughout the year. For example, on August 20 the vertical rays of the Sun are striking 12° N, whereas on October 15 they are striking 8° S. The values across the top of the analemma show the equation of time—the number of minutes that solar noon is fast or slow compared with mean (average) time.

of daylight gradually increases, reaching 12 hours of daylight on the March equinox. After the equinox, day length continues to increase until the longest day of the year on the June solstice. (During this period, day length is diminishing in the Southern Hemisphere.) Following the longest day of the year in the Northern Hemisphere on the June solstice, the pattern is reversed, with the days getting shorter in the Northern Hemisphere— reaching 12 hours on the September equinox, and then diminishing until the shortest day of the year on the December solstice. (During this period, day length is increasing in the Southern Hemisphere.) Overall, the annual variation in day length is the least in the tropics and greatest in the high latitudes (Table 1-3). Learning Check 1-16

On which days of the year do the vertical rays of the Sun strike the equator?

Day Length in the Arctic and Antarctic:The patterns of day and night in the Arctic and Antarctic deserve special mention. For an observer exactly at the North Pole,

the Sun rises on the March equinox and is above the horizon continuously for the next six months—circling the horizon higher and higher each day until the June solstice, after which it circles lower and lower until setting on the September equinox. Week by week after the March equinox, the region experiencing 24 hours of daylight grows, extending from the North Pole until the June solstice—when the entire region from the Arctic Circle to the North Pole experiences 24 hours of daylight. Following the June solstice, the region in the Arctic experiencing 24 hours of daylight diminishes week by week until the September equinox— when the Sun sets at the North Pole and remains below the horizon continuously for the next six months. Week by week following the September equinox, the region experiencing 24 hours of darkness extends from the North Pole until the December solstice—when the entire region from the Arctic Circle to the North Pole experiences 24 hours of darkness. Following the December solstice, the region experiencing 24 hours of darkness diminishes week by week until the March equinox—when the Sun again rises at the North Pole. In the Antarctic region of the Southern Hemisphere, these seasonal patterns are simply reversed.

Significance of Seasonal Patterns Both day length and the angle at which the Sun’s rays strike Earth determine the amount of solar energy received at any particular latitude. As a generalization, the higher the Sun is in the sky, the more effective is the warming. Day length influences patterns of solar energy receipt on Earth as well. For example, short periods of daylight in winter and long periods of daylight in summer contribute to seasonal differences in temperature in the mid- and high latitude regions of Earth. Thus, the tropical latitudes are generally always warm because they always have high Sun angles and consistent day lengths that are close to 12 hours long. Conversely, the polar regions are consistently cold because they always have low Sun angles—even the 24-hour days in

24Physical Geography: A Landscape Appreciation

summer do not compensate for the low angle of incidence of sunlight. Seasonal temperature differences are large in the midlatitudes because of sizable seasonal variations in Sun angles and length of day. This topic will be explored further in Chapter 4. Learning Check 1-17

For how many months of the year does the North Pole go without sunlight?

TELLING TIME Comprehending time around the world depends on an understanding of both the geographic grid of latitude and longitude, and of Earth–Sun relations. As Malcolm Thomson, a Canadian authority on the physics of time has noted, there are really only three natural units of time: the tropical year, marked by the return of the seasons; the lunar month, marked by the return of the new moon; and the day, marked by passage of the Sun. All other units of time measurement—such as a second, an hour, or a century—are human-made to meet the needs of society. In prehistoric times, the rising and setting of the Sun were probably the principal means of telling time. As civilizations developed, however, more precise timekeeping was required. Early agricultural civilizations in Egypt, Mesopotamia, India, China, and England, as well as the Aztec and Mayan civilizations in the Western Hemisphere, observed the Sun and the stars to tell time and keep accurate calendars. Local solar noon can be determined by watching for the moment when objects cast their shortest shadows. The Romans used sundials to tell time (Figure 1-30) and gave great importance to the noon position, which they called the meridian—the Sun’s highest (meri) point of the day (diem). Our use of A.M. (ante meridian: “before noon”) and P.M. (post meridian: “after noon”) was derived from the Roman world. When nearly all transportation was by foot, horse, or sailing vessel, it was difficult to compare time at different localities. In those days, each community set its own time by correcting its clocks to high noon at the moment of the shortest shadow. A central public building, such as a temple in India or a county courthouse in Kansas, usually

had a large clock or loud bells to toll the hour. Periodically, this time was checked against the shortest shadow.

Standard Time As the telegraph and railroad began to speed words and passengers between cities, the use of local solar time created increasing problems. A cross-country rail traveler in the United States in the 1870s might have experienced as many as 24 different local time standards between the Atlantic and Pacific coasts. Eventually, the railroads stimulated the development of a standardized time system. At the 1884 International Prime Meridian Conference in Washington, D.C., countries agreed to divide the world into 24 standard time zones, each extending over 15° of longitude. The mean local solar time of the Greenwich (prime) meridian was chosen as the standard for the entire system. The prime meridian became the center of a time zone that extends 7.5° of longitude to the west and 7.5° to the east of the prime meridian. Similarly, the meridians that are multiples of 15° both east and west of the prime meridian, were set as the central meridians for the 23 other time zones (Figure 1-31). Although Greenwich Mean Time (GMT) is now referred to as Universal Time Coordinated (UTC), the prime meridian is still the reference for standard time. Because it is always the same number of minutes after the hour in all standard time zones (keeping in mind that a few countries, such as India, do not adhere to standard one-hour-interval time zones), to know the exact local time, we usually need to know only how many hours later or earlier our local time zone is compared to the time in Greenwich. Figure 1-31 shows the number of hours later or earlier than UTC it is in each time zone of the world. Most of the countries of the world are sufficiently small in their east–west direction so as to lie totally within a single time zone. However, large countries may encompass several zones: Russia occupies nine time zones; including Alaska and Hawai‘i, the United States spreads over six (Figure 1-32); Canada, six; and Australia, three. In international waters, time zones are defined to be exactly 7°30´ to the east and 7°30´ to the west of the central meridians. Over land areas, however, zone boundaries vary to coincide with appropriate political and economic boundaries. For example, continental Europe from Portugal to Poland shares one time zone, although longitudinally covering about 30°. At the extreme, China extends across four 15° zones, but the entire nation, at least officially, observes the time of the 120° east meridian, which is the one closest to Beijing. In each time zone, the central meridian marks the location where clock time is the same as mean Sun time

◀Figure 1-30 A typical sundial. The edge of the vertical gnomon slants

upward from the dial face at an angle equal to the latitude of the sundial, pointing toward the North Pole in the Northern Hemisphere and the South Pole in the Southern Hemisphere. As the Sun appears to move across the sky during the course of a day, the position of the shadow cast by the gnomon changes. The time shown in this photograph of a sundial in Cornwall, United Kingdom, is about 11:00 A.M.

CHAPTER 1Introduction to Earth25 12 Midn

1 AM

2 AM

3 AM

4 AM

5 AM

6 AM

7 AM

8 AM

9 AM

10 AM

11 12 AM Noon

1 PM

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Prime Meridian

11 PM

International Date Line

London (Greenwich) 8:30 3:30 4:30

5:45 5:30 5:30

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Non-standard time

180°

150°W

120°W

90°W

60°W

30°W

30°E

60°E

90°E

120°E

150°E

▲Figure 1-31 The 24 time zones of the world, each based on central meridians spaced 15° apart. Especially over land areas, these boundaries

have been significantly adjusted.

(i.e., the Sun reaches its highest point in the sky at 12:00 noon). On either side of that meridian, of course, clock time does not coincide with Sun time. The deviation between the two is shown for one U.S. zone in Figure 1-33. From the map of time zones of the United States (Figure 1-32), we can recognize a great deal of manipulation of the time zone boundaries for economic and political convenience. For example, the Central Standard Time Zone, centered on 90° W extends all the way to 105° W (which is the central meridian of the Mountain Standard Time Zone) in Texas to keep most of that state within the same zone. By contrast, El Paso, Texas, is officially within the Mountain Standard Time Zone in accord with its role as a major market center for southern New Mexico, which observes Mountain Standard Time. In the same vein, northwestern Indiana is in the Central Standard Time Zone with Chicago. Learning Check 1-18

What happens to the hour when crossing from one time zone to the next going from west to east?

International Date Line In 1519, Ferdinand Magellan set out westward from Spain, sailing for East Asia with 241 men in five ships. Three years later, the remnants of his crew (18 men in one ship) successfully completed the first circumnavigation of the globe. Although a careful log had been kept, the crew found that their calendar was one day short of the correct date. This was the first human experience with time change on a global scale, the realization of which eventually led to the establishment of the International Date Line. One advantage of establishing the Greenwich meridian as the prime meridian is that its opposite arc is in the Pacific Ocean. The 180th meridian, transiting the sparsely populated mid-Pacific, was chosen as the meridian at which new days begin and old days exit from the surface of Earth. The International Date Line deviates from the 180th meridian in the Bering Sea to include all of the Aleutian Islands of Alaska within the same day and again in the South Pacific to keep islands of the same group (Fiji, Tonga) within the same day

26Physical Geography: A Landscape Appreciation

N

60° N

60°

◀Figure 1-32 Times zones for Canada,

(GMT –3)

Alaska Standard Time –9

W

the United States, and northern Mexico. The number in each time zone refers to the number of hours earlier than UTC (GMT).

16

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°N 50

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cer

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Dallas

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(Figure 1-34). The extensive eastern displacement of the date line in the central Pacific is due to the widely scattered locations of the many islands of the country of Kiribati. The International Date Line is in the middle of the time zone defined by the 180° meridian. Consequently, there is no time (i.e., hourly) change when crossing the International Date Line—only the calendar changes, not the clock. When you cross the International Date Line going from west to east, it becomes one day earlier (e.g., from January 2 to January 1); when you move across the line from east to west, it becomes one day later (e.g., from January 1 to January 2). What happens to the day when crossing the International Date Line going from west to east?

Houston

Minutes ahead

of

Learning Check 1-19

New Orleans

60 min.

ic Trop

20 min.

90°W

Minutes behind

▲Figure 1-33 Standard clock time versus Sun time. The Sun reaches its

highest point in the sky at 12:00 noon in St. Louis and New Orleans because these two cities lie on the central meridian. For places east of the central meridian, the Sun is highest in the sky a few minutes before standard time noon; for locations west, local solar noon is a few minutes after. In Chicago, for instance, the Sun is highest in the sky at 11:50 A.M. and in Dallas it is highest in the sky at 12:28 P.M.

Daylight-Saving Time To conserve energy during World War I, Germany ordered all clocks set forward by an hour. This practice allowed the citizenry to “save” an hour of daylight by shifting the daylight period into the usual evening hours, thus reducing the consumption of electricity for lighting. The United States began a similar policy in 1918, but

day

Aleutian Islands

Da

Sun

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r na tio te L nal ine

CHAPTER 1Introduction to Earth27

Sat

urd ay

180

°

Samoa Tonga

many localities declined to observe “summer time” until the Uniform Time Act made the practice mandatory in all states that had not deliberately exempted themselves. Hawai‘i, and parts of Indiana and Arizona, have exempted themselves from observance of daylight-saving time under this act. Russia has adopted permanent daylight-saving time (and double daylight-saving time—two hours ahead of Sun time—in the summer). In recent years, Canada, Australia, New Zealand, and most of the nations of western Europe have also adopted daylight-saving time. In the Northern Hemisphere, many nations, like the United States, begin daylight-saving time on the second Sunday in March (in the spring we “spring forward” one hour) and resume standard time on the first Sunday in November (in the fall we “fall back” one hour). In the tropics, the lengths of day and night change little seasonally, and there is not much twilight. Consequently, daylight-saving time would offer little or no savings for tropical areas.

▲Figure 1-34 The International Date Line generally follows the 180th

meridian, but it deviates around various island groups, most notably Kiribati.

Chapter 1

LEARNING REVIEW After studying this chapter, you should be able to answer the following questions. Key terms from each text section are shown in bold type. Definitions for key terms are also found in the glossary at the back of the book.

KEY TERMS AND CONCEPTS Geography and Science (p. 3) 1. Contrast physical geography and cultural geography. 2. If an idea cannot be disproven by some possible observation or test, can such an idea be supported by science? Explain. 3. What is the approximate English System of measurement equivalent of one kilometer in the International System (S.I.)?

Environmental Spheres and Earth Systems (p. 7) 4. Briefly describe the environmental “spheres”: atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere. 5. Contrast closed systems and open systems. 6. What does it mean when a system is in equilibrium? 7. How does a positive feedback loop differ from a negative feedback loop?

Earth and the Solar System (p. 10) 8. In what ways do the inner and outer planets (the terrestrial and Jovian planets) of our solar system differ from each other? 9. Compare the size of Earth to that of its surface features and atmosphere. 10. Is Earth perfectly spherical? Explain.

The Geographic Grid—Latitude and Longitude (p. 13) 11. Define the following terms: latitude, longitude, parallel, meridian, and prime meridian. 12. Latitude ranges from _____° to _____° north and south, whereas longitude ranges from _____° to _____° east and west. 13. State the latitude (in degrees) for the following “special” parallels: equator, North Pole, South Pole, Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and Antarctic Circle.

28Physical Geography: A Landscape Appreciation

14. What is a great circle? A small circle? Provide examples of both.

Earth–Sun Relations and the Seasons (p. 17) 15. Describe and explain the four factors in Earth–Sun relations associated with the change of seasons: rotation, revolution around the Sun, inclination of Earth’s axis, and polarity (parallelism) of Earth’s axis. 16. Does the plane of the ecliptic coincide with the plane of the equator? Explain. 17. On which day of the year is Earth closest to the Sun (perihelion)? Farthest from the Sun (aphelion)? 18. Provide the approximate date for the following special days of the year: March equinox, June solstice, September equinox, and December solstice. 19. What is the circle of illumination? 20. What is meant by the solar altitude? 21. Briefly describe Earth’s orientation to the Sun during the Northern Hemisphere summer and the Northern Hemisphere winter. 22. Beginning with the March equinox, describe the changing latitude of the vertical rays of the noon Sun during the year. 23. In the midlatitudes of the Northern Hemisphere, on which day of the year is the Sun highest in the sky? Lowest in the sky?

24. For the equator, describe the approximate number of daylight hours on the following days of the year: March equinox, June solstice, September equinox, and December solstice. 25. What is the longest day of the year (the day with the greatest number of daylight hours) in the midlatitudes of the Northern Hemisphere? What is the longest day in the Southern Hemisphere? 26. For the North Pole, describe the approximate number of daylight hours on the following days of the year: March equinox, June solstice, September equinox, and December solstice. 27. For how many months of the year does the North Pole have no sunlight at all?

Telling Time (p. 24) 28. What happens to the hour when crossing a time zone boundary moving from west to east? 29. What is meant by UTC (Universal Time Coordinated) and Greenwich Mean Time (GMT)? 30. What happens to the day when crossing the International Date Line moving from east to west? 31. When daylight-saving time begins in the spring, you would adjust your clock from 2:00 A.M. to _____.

STUDY QUESTIONS 1. Why are physical geographers interested in globalization of the economy? 2. Why is a distance covered by 1° of longitude at the equator different from the distance covered by 1° of longitude at a latitude of 45° N? 3. What is the significance of aphelion and perihelion in Earth’s seasons? 4. In terms of the change of seasons, explain the significance of the Tropic of Cancer, the Tropic of Capricorn, the Arctic Circle, and the Antarctic Circle. 5. Is the noon Sun ever directly overhead in Madison, Wisconsin (43° N)? If not, on which day of the year is the noon Sun highest in the sky there, and on which day is it lowest?

6. What would be the effect on the annual march of the seasons if Earth’s axis was not inclined relative to the plane of the ecliptic? 7. What would be the effect on the annual march of the seasons if the North Pole was always leaning toward the Sun? 8. If Earth’s axis was tilted only 20° from perpendicular, what would the latitudes of the Tropic of Cancer and Arctic Circle become? 9. Why are standard time zones 15° of longitude wide? 10. Most weather satellite images are “time-stamped” using UTC or “Zulu” time (UTC expressed using 24-hour or military time) instead of the local time of the region below. Why?

CHAPTER 1Introduction to Earth29

EXERCISES 1. Using formulas found in Appendix I (p. A-1), make the following conversions between the International System (S.I.) and English systems of measurements: a. 12 centimeters = _____ inches b. 140 kilometers = _____ miles c. 12,000 feet = _____ meters d. 3 quarts = _____ liters e. 5 kilograms = _____ pounds f. 10°C = _____ °F 2. Using a world map or globe, estimate the latitude and longitude of both New York City and Sydney, Australia. Be sure to specify if these locations are north or south latitude, and east or west longitude. 3. The solar altitude (the angle of the noon Sun above the horizon) can be calculated for any latitude on Earth for any day of the year, by using the formula: SA = 90° – AD, where SA is the “solar altitude” and

AD is the “arc distance” (the difference in latitude between the declination of the Sun and the latitude in question). Use the analemma (Figure 1-29) to determine the declination of the Sun, and then calculate the solar altitude at the following locations on the day given: a. Beijing, China (40° N) on November 25th b. Nairobi, Kenya (1° S) on September 25th c. Fairbanks, Alaska (65° N) on July 10th 4. Using the map of North American time zones (Figure 1-32) for reference, if it is 5:00 P.M. standard time on Thursday in New York City (41° N, 74° W), what is the day and time in Los Angeles (34° N, 118° W)? 5. Using the map of world time zones (Figure 1-31) for reference, if it is 11:00 A.M. UTC (Universal Time Coordinated or Greenwich Mean Time), what is the standard time in Seattle (48° N, 122° W)?

Seeing Geographically Look again at the image of Earth at the beginning of the chapter (p. 2). What evidence can you see of each of Earth’s “spheres” in this image? What is the approximate latitude and longitude of the center of the image? Based on the position of the circle of illumination, is it early morning or late afternoon in Beijing, China? Generally, how do the clouds look different in the tropics compared with the clouds in higher latitudes?

Looking for additional review and test prep materials? Visit the Study Area in MasteringGeography™ to enhance your geographic literacy, spatial reasoning skills, and understanding of this chapter’s content by accessing a variety of resources, including geoscience animations, interactive maps, videos, RSS feeds, flashcards, web links, self-study quizzes, and an eText version of McKnight’s Physical Geography: ALandscape Appreciation.

Chapter 2

PORTRAYING EARTH

THE SURFACE OF EARTH IS THE FOCUS OF THE GEOGRAPHER’S interest. The enormity and complexity of this surface would be difficult to comprehend and analyze without tools to systematically organize the varied data. Although many kinds of tools are used in geographic studies, the most important are maps. The mapping of a geographic feature is often an essential first step toward understanding the spatial distributions and relationships of that feature. This book is a case in point—it contains numerous maps of various kinds, each included to further your understanding of some concept, fact, or relationship. The purpose of this chapter is twofold: (1) To describe the basic characteristics of maps, including their capabilities and limitations; and (2) to describe the various ways a landscape can be portrayed—through maps, globes, photographs, and remotely sensed imagery (Figure 2-1). As you study this chapter, think about these key questions: r Why can no map of the world be as accurate as a globe? r What is meant by the scale of a map, and what are the different ways that map scale is described? r What are the differences between equivalent (“equal area”) maps and conformal maps, and when are these properties most important in geographic studies? r How do the four major families of map projections differ from each other, and what are some of the best uses for maps in each of these families of projections? r How are isolines used to convey information on a map? r How does a GPS unit know where we are, and what are some common uses of GPS? r What is remote sensing, and what kinds of information can be gathered in this way? r How does GIS help in the analysis of geographic data?

MAPS AND GLOBES For portraying the geographic features of Earth as a whole, there is no substitute for a globe (Figure 2-2). Not only does a well-made globe accurately convey the spherical shape of Earth, it can show, essentially without distortion, the spatial relationships of Earth’s surface, maintaining correct size, shape, distance, and direction relationships of features around the planet. A globe, of course, has limitations. Most importantly, almost all globes are constructed at a very small scale, which means that they cannot show much detail. In order for a globe to show as much detail as the maps in Figure 2-1, it would need to be about 500 meters (1600 feet) in diameter! Because maps are much more portable and versatile than globes, there are literally billions of maps in use over the world, whereas globes are extremely limited both in number and variety.

Seeing Geographically This natural color satellite image of Baja, Mexico, was taken on November 27, 2011, with the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument aboard NASA’s Aqua satellite. Strong winds have caused dust to blow off of mainland Mexico and the Baja peninsula. From which direction were the winds blowing on this day? How do the mountaintops and sky conditions change as you look north of Mexico into the United States? 31

32Physical Geography: A Landscape Appreciation

(a) High-resolution orthoimagery (b) Topographic map

(c) Geologic map (d) Google map ▲Figure 2-1 Different types of maps convey different kinds of information about the landscape, as shown in

these four maps of a region near Salem, Massachusetts. (a) High-resolution orthophoto imagery (original scale 1:24,000). (b) Topographic map with elevation contour lines (original scale 1:24,000). (c) Geologic map showing rock types: orange = coarse glacial deposits; blue = glaciomarine deposits; green = glacial till; lavender = swamp deposits (original scale 1:50,000). (d) Google™ Map showing streets and highways.

Maps In the simplest terms, a map is a flat representation of Earth, shown reduced in size with only selected features or data showing. A map serves as a surrogate (a substitute) for any surface we wish to portray or study. Although any kind of surface can be mapped—the lunar surface, for instance, or that of Mars—all the maps in this book portray portions of Earth’s surface. The basic attribute of maps is their ability to show distance, direction, size, and shape in their horizontal (that is to say, two-dimensional) spatial relationships. In addition to these fundamental graphic data, most maps

show other kinds of information as well. Most maps have a special purpose, and that purpose is usually to show the distribution of one or more phenomena (seeFigure2-1). Such thematic maps may be designed to show street patterns, the distribution of Tasmanians, the ratio of sunshine to cloud, the number of earthworms per cubic meter of soil, or any of an infinite number of other facts or combinations of facts. Because they depict graphically “what is where” and because they are often helpful in providing clues as to “why” such a distribution occurs, maps are indispensable tools for geographers. Even so, it is important to realize that maps have limitations.

CHAPTER 2Portraying Earth33

it possible to measure distance, determine area, and compare sizes. Because Earth’s surface is curved and a map’s surface is flat, scale can never be perfectly correct over an entire map. In practice, if the map is of a small area a single scale can be used across the entire map. However, if the map is showing a large portion of Earth’s surface (such as a world map), there may be significant scale differences from one part of the map to the next—such a map, for example, might need to list different scales for different latitudes.

Scale Types Three ways of portraying map scale are widely used: the graphic scale, the fractional scale, and the verbal scale (Figure 2-3).

▲Figure 2-2 A model globe provides a splendid broad representation

ofEarth at a very small scale, but few details can be portrayed.

Map Distortions:Although most people understand that not everything we may read in a book, in a newspaper, or on the Internet is necessarily correct (thus the somewhat cynical adage, “Don’t believe everything you read”), these same people may uncritically accept all information portrayed on a map as being correct. However, no map can be perfectly accurate because it is impossible to portray the curved surface of Earth on a flat map without distortion. Imagine trying to flatten an orange peel—in order to do this, you must either stretch or tear the peel; effectively, the same thing must happen to Earth when we flatten its surface onto a map. The extent to which the geometric impossibility of flattening a sphere without distortion becomes a problem on a map depends on two related variables. First: how much of Earth is being shown on the map—for example, these distortions are always significant on a world map, but less so on a map showing a very limited region of Earth. Second: the scale of the map—the topic to which we turn next.

Graphic Map Scales:A graphic map scale uses a line marked off in distances to represent actual distance on Earth’s surface. To use a graphic map scale, we measure off the distance between two points on the map (such as by making two pencil marks along the edge of a piece of paper), and then compare that measured distance to the graphic map scale—the graphic scale gives you a direct reading of the actual distance. The advantage of a graphic scale is its simplicity: you determine approximate distances on the surface of Earth by measuring them directly on the map (such as a motorist can do to estimate travel distances on a road map). Moreover, a graphic scale remains correct when a map is enlarged or reduced in size because the length of the graphic scale line is also changed as the map size is changed. Fractional Map Scales:A fractional map scale conveys the relationship between distance measured on a map and the actual distance that represents on Earth with a fraction or ratio called a representative fraction. For example,

Learning Check 2-1

Why can’t a map representEarth’s surface as perfectly as a globe? (Answer on p.AK-1)

MAP SCALE Because a map is smaller than the portion of Earth’s surface it represents, in order to understand the geographic relationships (distances or relative sizes, for example) depicted on that map, we must know how to use a map scale. The scale of a map describes the relationship between distance measured on the map and the actual distance that represents on Earth’s surface. Knowing the scale of a map makes

▲Figure 2-3 All three types of scale are shown on this map. Included

area fractional scale, a verbal scale, and a graphic (shown inboth miles and kilometers).

34Physical Geography: A Landscape Appreciation

acommon fractional scale uses the representative fraction 1/63,360 (often expressed as the ratio 1:63,360): this notation means that 1 unit of measure on the map represents an actual distance of 63,360 units of measure on Earth. The “units of measure” are the same on both sides of the fraction, so 1 millimeter measured on the map represents an actual distance of 63,360 millimeters on Earth’s surface, whereas 1 inch measured on the map represents an actual distance of 63,360 inches on Earth’s surface, and so forth.

Learning Check 2-2 On a map with a fractional scale of 1:10,000, one centimeter measured on the map represents what actual distance on Earth’s surface?

Large and Small Scale Maps The adjectives large and small are comparative rather than absolute. In other words, scales are “large” or “small” only in comparison with other scales (Figure 2-4). A large-scale map is one that has a relatively large representative fraction, which means that the denominator is small. Thus, 1/10,000 is a larger value than, say, 1/1,000,000, and so a scale of 1:10,000 is large in comparison with one of 1:1,000,000; consequently, a map at a scale of 1:10,000 is called a large-scale map—such a map portrays only a small portion ofEarth’s surface but portrays it in considerable detail. Forexample, if

Verbal Map Scales:A verbal map scale (or word scale) states in words the relationship between the distance on the map and the actual distance on Earth’s surface, such as “one centimeter to ten kilometers” or “one inch equals five miles.” A verbal scale is simply a mathematical manipulation of the fractional scale. For instance, there are 63,360 inches in 1 mile, so on a map with a fractional scale of 1:63,360 we can say that “1 inch represents 1 mile.”

1 in. = 1600 mi or 1 cm = 1014 km

(Verbal scale)

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CANADA

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10th St NE

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and area at various map scales. A small-scale map portrays a large part of Earth's surface but depicts onlythemost important features, whereas alarge-scale map shows only a small part of thesurface butinconsiderably more detail.

Moreland Ave SE

▲Figure 2-4 Comparisons of distance

y R Ke

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5 Kilometers

CHAPTER 2Portraying Earth35

this page were covered with a map having a scale of 1:10,000, the map would be able to show just a small part of a single city, but that area would be rendered in great detail. A small-scale map has a small representative fraction— in other words, one having a large denominator. A map having a scale of 1:10,000,000 is classified as a small-scale map. If it were covered with a map of that scale, this page would be able to portray about one-third of the United States, but only in limited detail.

MAP PROJECTIONS ANDPROPERTIES The challenge to the cartographer (mapAnimation Map Projections maker) is to try to combine the geometric exactness of a globe with the convenience of a flat map. This melding has been attempted for many centuries, and further refinements continue to be made. The fundamental problem is always the same: to transfer data from a spherical surface to a flat map with a minimum of distortion. This transfer is accomplished with a map projection.

Map Projections A map projection is a system in which the spherical surface of Earth is transformed for display on a flat surface. The basic principle of a map projection is simple. Imagine a transparent globe on which are drawn meridians, parallels, and continental boundaries; also imagine a lightbulb in the center of this globe. A piece of paper, either held flat or rolled into some shape such as a cylinder or cone, is placed over the globe as in Figure 2-5. When the bulb is lighted, all the lines on the globe are projected outward onto the paper. These lines are then sketched on the paper.

(a)

MERCATOR PROJECTION

(b) ▲Figure 2-5 The concept of map projection. A cylinder is wrapped

around a globe with a light in its center (a), and the features of the globe are projected onto the adjacent cylinder. (b) The resulting map is called a cylindrical projection.

When the paper is laid out flat, a map projection has been produced. Few map projections have been made by actual “optical” projection from a globe onto a piece of paper; instead, map projections are derived by mathematically transferring the features of a sphere onto a flat surface. Because a flat surface cannot be closely fitted to a sphere without wrinkling or tearing, no matter how a map projection is made, data from a globe (parallels, meridians, continental boundaries, and so forth) cannot be transferred to a map without distortion of shape, relative area, distance, and/or direction. However, the cartographer can choose to control or reduce one or more of these distortions—although all distortions cannot be eliminated on a single map. Learning Check 2-3

What is a map projection?

Map Properties Cartographers often strive to maintain accuracy either of size or of shape—map properties known as equivalence and conformality, respectively (Figure 2-6). Equivalence:In an equivalent map projection (also called an equal area map projection) the correct size ratio of area on the map to the corresponding actual area on Earth’s surface is maintained over the entire map. For example, on an equivalent world map, if you were to place four dimes at different places (perhaps one on Brazil, one on Australia, one on Siberia, and one on South Africa), the area on Earth covered by each coin would be the same. Equivalent projections are very desirable because, with them, misleading impressions of size are avoided. The world maps in this book are mostly equivalent projections because they are so useful in portraying distributions of the various geographic features we will be studying. There are trade-offs, of course, with equivalent maps. Equivalence is difficult to achieve on small-scale maps because correct shapes must be sacrificed in order to maintain proper area relationships. Most equivalent world maps (which are necessarily small-scale maps) show distorted shapes of landmasses—especially in the high latitudes. For example, as Figure 2-6b shows, on equivalent maps the shapes of Greenland and Alaska are usually shown as more “squatty” than they actually are. Conformality:A conformal map projection is one in which proper angular relationships are maintained across the entire map so that the shapes of features such as coastlines are the same as on Earth. It is impossible to depict true shapes for large areas such as a continent, but they can be approximated, and in practice for small areas we can say that conformal maps show correct shapes. All conformal projections have meridians and parallels crossing each other at right angles, just as they do on a globe. The main problem with conformal projections is that the size of an area must often be considerably distorted to depict the proper shape. Thus, the scale necessarily changes from one region to another. For example, a

36Physical Geography: A Landscape Appreciation

80°N

80°N

60°N

60°N 40°N

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60°S

ECKERT PROJECTION

80°S

60°S

(b) Equivalent 80°S MERCATOR PROJECTION

(a) Conformal ▲Figure 2-6 Conformal and equivalent maps. (a) A conformal projection (the Mercator) depicts

accurate shapes, but the sizes are severely exaggerated in high latitudes. (b) An equivalent (equal area) projection (the Eckert) is accurate with regard to size, but shapes are badly distorted in high latitudes. It is impossible to portray both correct size and correct shape on a world map. Compare the sizes and shapes of Antarctica, Alaska, and Greenland in these examples.

conformal map of the world normally greatly enlarges sizes in the high latitudes. Figure 2-6a shows the conformal projection known as a Mercator projection (discussed in greater detail later in this chapter)—notice the exaggerated apparent sizes of landmasses toward the poles. Compromise Projections:Except for maps of very small areas (in other words, large-scale maps), where both properties can be closely approximated, conformality and equivalence cannot be maintained on the same projection, and thus the art of mapmaking, like politics, is often an art of compromise. For example, Figure 2-7 shows a Robinson projection—a compromise map projection; it is neither equivalent nor conformal, but instead balances reasonably accurate shapes with reasonably accurate areas. The Robinson projection is a popular choice as a general-purpose classroom map.

As a rule of thumb, it can be stated that some map projections are purely conformal, some are purely equivalent, none are both conformal and equivalent, and many are neither, but are instead a compromise between the two. Learning Check 2-4

What is the difference between an equivalent map and a conformal map?

FAMILIES OF MAP PROJECTIONS Because there is no way to avoid distortion completely, no map projection is ideal for all uses. So, hundreds of different map projections have been devised for one purpose or another. Most of them can be grouped into just a few families. Projections in the same family generally have similar properties and related distortion characteristics.

Cylindrical Projections

ROBINSON PROJECTION

▲Figure 2-7 Many world maps are neither purely conformal nor purely

equivalent, but a compromise between the two. One of the most popular compromises is the Robinson projection shown here.

As Figure 2-5 shows, a cylindrical projection is obtained by mathematically “wrapping” the globe with a cylinder of paper in such a way that the paper touches the globe only at the globe’s equator. We say that paper positioned this way is tangent to the globe at the equator, and the equator is called the circle of tangency (some cylindrical projections choose a circle of tangency other than the equator). The curved parallels and meridians of the globe then form a perfectly rectangular grid on the map. Having the equator as the tangency line produces a right-angled grid (meridians and parallels meet at right angles) on a rectangular

CHAPTER 2Portraying Earth37

map. There is no size distortion at the circle of tangency, but size distortion increases progressively with increasing distance from this circle, a characteristic clearly exemplified by the Mercator projection. Mercator: The Most Famous Projection:Although some map projections were devised centuries ago, projection techniques have improved right up to the present day. Thus, it is remarkable that the most famous of all map projections, the Mercator projection, originated in 1569 by a Flemish geographer and cartographer, is still in common usage today without significant modification (see Figure 2-6a). Gerhardus Mercator produced some of the best maps and globes of his time. His place in history, however, is based largely on the fact that he developed a specialpurpose projection that became inordinately popular for general-purpose use. The Mercator projection is a conformal map projection designed to facilitate oceanic navigation. The prime advantage of a Mercator map is that it shows loxodromes as straight lines. A loxodrome, also called a rhumb line, is a curve on the surface of a sphere that crosses all meridians at the same angle and represents a line of constant compass direction. A navigator first plots the shortest distance between origin and destination on a map projection in which great circles are shown as straight lines, such as the gnomonic projection shown in Figure 2-8a (great circle routes are discussed in Chapter 1), and then transfers that route to a Mercator projection with straight-line loxodromes. This procedure allows the navigator to generally take the shorter path of a great circle route by simply making periodic changes in the compass course of the airplane or ship. Today, of course, these calculations are all done by computer. A Mercator map is relatively undistorted in the low latitudes. However, because the meridians do not converge at the poles but instead remain parallel to each other, size distortion increases rapidly in the mid- and high latitudes. Further, to maintain conformality and the map’s navigational virtues, Mercator compensated for the east–west stretching by spacing the parallels of latitude increasingly farther apart so that north–south stretching occurs at the same rate. This procedure allowed shapes to be approximated with reasonable accuracy, but at great expense to proper size relationships. Area is distorted by 4 times at the 60th parallel of latitude and by 36 times at the 80th parallel. If the North Pole could be shown on a Mercator projection, it would be a line as long as the equator rather than a single point! The Mercator projection was a major leap forward in cartography when it was devised, and it remains an excellent choice for large-scale navigation maps and other uses where conformality is important. Unfortunately, by the early twentieth century, Mercator projections were widely used in American classrooms and atlases. Indeed, several generations of American students have passed through school with their principal view of the

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(c) Mercator Projection ▲Figure 2-8 The prime virtue of the Mercator projection is its

usefulness for straight-line navigation. (a) The shortest distance between two locations—here San Francisco and Yokohama—can be plotted on a gnomonic projection (on which great circles are shown as straight lines). (b) The great circle route can be transferred to a Mercator projection. (c) On the Mercator projection, straight-line loxodromes can then be substituted for the curved great circle. The loxodromes allow the navigator to maintain constant compass headings over small distances while still approximating the curve of the great circle.

world provided by a Mercator map. This has created many misconceptions, not the least of which is confusion about the relative sizes of high-latitude landmasses: on a Mercator projection, the island of Greenland appears to be as large as or larger than Africa, Australia, and South America. Actually, however, Africa is actually 14 times larger than Greenland, South America is 9 times larger, and Australia is 3.5 times larger. The Mercator projection was devised several centuries ago for a specific purpose, and it still serves that purpose well. Its fame, however, is significantly due to its misuse. Learning Check 2-5

Would a Mercator projection be a good choice for a map used to study the loss of forest cover around the world? Why or why not?

Planar Projections A planar projection (also called a plane, azimuthal, or zenithal projection) is obtained by projecting the markings of a center-lit globe onto a flat piece of paper that is tangent to the globe at one point (Figure 2-9)—usually the North or South Pole, or some point on the equator. There

38Physical Geography: A Landscape Appreciation

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(a) ▲Figure 2-11 The origin of a conic projection, as illustrated by a globe

with a light in its center (a), projecting images onto a cone. (b) The resulting map is called a conic projection.

just as it is with a globe, although planar projections can be useful for focusing attention on a specific region, and they are common projections when mapping the Arctic and Antarctic regions.

Conic Projections

80°N

A conic projection is obtained by projecting the markings of a center-lit globe onto a cone wrapped tangent to, or intersecting, a portion of the globe (Figure 2-11). Normally the apex of the cone is positioned above a pole, which means that the circle of tangency coincides with a parallel. This parallel then becomes the standard parallel of the projection; distortion is least in its vicinity and increases progressively as one moves away from it. Consequently, conic projections are best suited for regions of east–west orientation in the midlatitudes, being particularly useful for maps of the United States, Europe, or China. It is impractical to use conic projections for more than one-fourth of Earth’s surface (a semihemisphere), but they are particularly well adapted for mapping relatively small areas, such as a state or county.

60°N

Pseudocylindrical Projections

▲Figure 2-9 The origin of a planar projection, as illustrated by a globe

with a light in its center, projecting images onto an adjacent plane. The resulting map goes by various names: azimuthal projection, plane projection, or zenithal projection.

is no distortion immediately around the point of tangency, but distortion increases progressively away from this point. Typically, planar projections show only one hemisphere, and some types can provide a perspective of Earth similar to the view one gets when looking at a globe or that of an astronaut looking at Earth from space (Figure 2-10). This half-view-only characteristic can be a drawback, of course,

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▲Figure 2-10 An orthographic planar projection showing Earth as it

would appear from space.

A pseudocylindrical projection (also called an elliptical or oval projection) is a roughly football-shaped map, usually of the entire world (see the Eckert in Figure 2-6b and the Robinson in Figure 2-7), although sometimes only the central section of a pseudocylindrical projection is used for maps of lesser areas. Mathematically, a pseudocylindrical projection wraps around the equator like an ordinary cylindrical projection, but then further “curves in” toward the poles, effectively conveying some of the curvature of Earth. In most pseudocylindrical projections, a central parallel (usually the equator) and a central meridian (often the prime meridian) cross at right angles in the middle of the map, which is a point of no distortion; distortion in size and/or shape normally increases progressively as one moves

CHAPTER 2Portraying Earth39

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away from this point in any direction. All of the parallels are drawn parallel to each other, whereas all meridians, except the central meridian, are shown as curved lines.

Learning Check 2-6

What are the advantages of an “interrupted” projection, such as the Goode’s projection?

Interrupted Projections: One technique used with pseudocylindrical projections to minimize distortion of the continents is to “interrupt” oceanic regions—Goode’s interrupted homolosine equal-area projection (Figure 2-12) is a popular example of this. Goode’s projection is equivalent, and, although it is impossible for this map to be conformal, the shapes of continental coastlines are very well maintained even in high latitudes. When global distributions are mapped, the continents are often more important than the oceans, and yet the oceans occupy most of the map space in a typical projection. A projection can be interrupted (“torn apart”) in the Pacific, Atlantic, and Indian Oceans and then based on central meridians that pass through each major landmass— with no land area far from a central meridian, shape and size distortion is greatly decreased. For world maps that emphasize ocean areas, continents can be interrupted instead of ocean basins. You’ll see that many of the maps used in this book employ variations of Goode’s interrupted projection.

CONVEYING INFORMATION ONMAPS Now that we have described the fundamentals of map scale, properties and projections, let’s think about some of the ways that information is presented on maps. We begin with basic features of all maps.

Map Essentials Maps come in an infinite variety of sizes and styles and serve a limitless diversity of purposes. Regardless of type, however, every map should contain a few basic components to facilitate its use (Figure 2-13). Omission of any of these essential components decreases the clarity of the map and may make it more difficult to interpret. ◀Figure 2-13 A typical thematic

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the world. The purpose of the interruptions is to portray certain areas (usually continents) more accurately, at the expense of portions of the map (usually oceans) that are not important to the map’s theme. The map shown here is a Goode’s interrupted homolosine equal-area projection. A variation of this projection is used for many maps in this book.

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40Physical Geography: A Landscape Appreciation

Title:This should be a brief summary of the map’s content or purpose. It should identify the area covered and provide some indication of content, such as “Road Map of Kenya,” or “River Discharge in Northern Europe.” Date:This should indicate the time span over which the information was collected. In addition, some maps also give the date of publication of the map. Most maps depict conditions or patterns that are temporary or even momentary. For a map to be meaningful, therefore, the reader must be informed when the data were gathered, as this information indicates how timely or out of date the map is. Legend:Most maps use symbols, colors, shadings, or other devices to represent features or the amount, degree, or proportion of some quantity. Some symbols are self-explanatory, but it is usually necessary to include a legendbox in a corner of the map to explain the symbolization. Scale:Any map that serves as more than a pictogram must be drawn to scale, at least approximately. A graphic, verbal, or fractional scale is, therefore, necessary. Direction: Direction is normally shown on a map by means of the geographic grid of parallels and meridians. If no grid is shown, direction may be indicated by a straight arrow pointing northward, which is called a north arrow.

Anorth arrow is aligned with the meridians and thus points toward the north geographic pole. Location:Although the grid system of latitude and longitude is the most common system of location seen on maps, other types of reference grids may also be used on maps. For example, some large-scale maps (such as road maps) use a simple x- and y-coordinate grid to locating features (similar to that shown in Figure 1-11), and some maps display more than one coordinate system. Data Source:For most thematic maps, it is useful to indicate the source of the data. Projection Type:On many maps, particularly small-scale ones, the type of map projection is indicated to help the user assess the kinds of distortions on the map.

Isolines Maps can display data in a number of different ways. One of the most widespread techniques for portraying the geographic distribution of some phenomenon is the isoline (from the Greek isos, meaning “equal”). Isoline is a generic term that refers to any line that joins points of equal value of something. Some isolines represent tangible surfaces, such as the elevation contour lines on a topographic map (Figure2-14). Most, however, signify such intangible features as

Hilltop Small ridge

▶Figure 2-14 This portion of a

typical United States Geological Survey topographic map quadrangle illustrates the use of contour lines, shown here with a matching landscape diagram and labeled features. This is a section of the Fillmore, California, quadrangle. Theoriginal map scale was 1:24,000; the contour interval is 40 feet (12 meters).

Valley floor

CHAPTER 2Portraying Earth41

temperature and precipitation, and some express relative values such as ratios or proportions (Figure 2-15). More than 100 kinds of isolines have been identified by name, ranging from isoamplitude (used to describe radio waves) to isovapor (water vapor content of the air), but only a few types are important in an introductory physical geography course:

40°N

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t Elevation contour line—a line joining points of equal elevation (see Appendix II for a description of U.S. Geological Survey topographic maps) t Isotherm—a line joining points of equal temperature t Isobar—a line joining points of equal atmospheric pressure t Isohyet—a line joining points of equal quantities of precipitation (hyeto is from the Greek, meaning “rain”) t Isogonic line—a line joining points of equal magnetic declination

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AVERAGE ANNUAL PRECIPITATION cm. in. 200 and 80 and over over 150–199 60–79

Drawing Isolines:To draw an isoline on a map, it is often necessary to estimate values that are not available. As a simple example, Figure 2-16 illustrates the basic steps in constructing an isoline map—in this case, an elevation contour line map. Each dot in Figure 2-16a represents a data collection location, and the number next to each dot is the elevation above sea level in meters. We begin by drawing the 115-meter elevation contour: the 115-meter contour line passes between 114 and 116, and between 113 and 116 (Figure 2-16b). In Figure 2-16c this estimation process is repeated for other elevation contours, and in Figure 2-16d shading is added to clarify the pattern.

Each dot shows the location of a data point with its elevation in meters

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▲Figure 2-15 Isolines can be used to show the spatial variation of

even intangible features, such as in this map that shows average annual precipitation for the continent of Africa (on this map the areas between isolines have been shaded to clarify the pattern).

The 115-meter contour line passes between 114 and 116, and between 113 and 116

The estimation process is repeated and the other contours are drawn at 5-meter intervals

Shading is added to clarify the pattern

(a) (b) (c)

(d) ▲Figure 2-16 Drawing isolines. (a) Each dot represents an elevation above sea level in meters.

(b) The 115-meter elevation contour is drawn. (c) The other contour lines at 5-meter intervals are drawn. (d) Shading is added for clarity.

Elevation in meters

42Physical Geography: A Landscape Appreciation

Characteristics of Isolines:The basic characteristics of isolines include: t $PODFQUVBMMZ JTPMJOFTBSFBMXBZTDMPTFEMJOFTUIBUJT they have no ends. In practice, however, an isoline often extends beyond the edge of a map, such as in Figure 2-16. t #FDBVTFUIFZSFQSFTFOUHSBEBUJPOTJORVBOUJUZ JTPMJOFT can never touch or cross one another, except under special circumstances. t 5IFOVNFSJDBMEJGGFSFODFCFUXFFOPOFJTPMJOFBOEUIF next is called the interval. Although intervals can be varied according to the wishes of the mapmaker, it is normally more useful to maintain a constant interval all over a given map. t *TPMJOFTDMPTFUPHFUIFSJOEJDBUFBTUFFQHSBEJFOU (in other words, a rapid change); isolines far apart indicate a gentle gradient. Edmund Halley (1656–1742), an English astronomer and cartographer (for whom Halley’s Comet is named), was not the first person to use isolines, but in 1700 he produced a map that was apparently the first published map to have isolines. This map showed isogonic lines in the Atlantic Ocean. Isoline maps are now commonplace and are very useful to geographers even though an isoline is an artificial construct—that is, it does not occur in nature. For instance, an isoline map can reveal spatial relationships that might otherwise go undetected. Patterns that are too large, too abstract, or too detailed for ordinary comprehension are often significantly clarified by the use of isolines. Learning Check 2-7

Define “isoline” and give one example of a kind of distribution pattern that can be mapped with isolines.

Portraying the Three-Dimensional Landscape Although many maps are simply flat representations of Earth, in physical geography the vertical aspect of the landscape is often an important component of study. In addition to actual raised-relief models of landforms, many other methods can be used to convey the three-dimensional aspect of the landscape on a two-dimensional map. Elevation Contours:For many decades, topographic maps using elevation contour lines were a workhorse of landform study (see Figure 2-14)—and remain so today even as we transition from traditional paper maps to electronic maps such as those available from the U.S. Geological Survey (USGS) on its online National Map site (http:// nationalmap.gov/). Topographic maps and contour line rules are discussed in detail in Appendix II. Digital Elevation Models:A remarkable recent advance in cartography has been the use of digital elevation models (DEM) to convey topography. The starting point for creating a DEM image is a detailed database of precise elevations. For example, the USGS maintains such a

▲Figure 2-17 An oblique shaded-relief digital elevation model of post-

1980 eruption Mount St. Helens.

database for the United States at several different spatial resolutions—a 30-meter grid being one of the most commonly used (meaning that elevation data are available at distance intervals of 30 meters, both north–south and east–west, across the entire country). Similar digital elevation data are increasingly available for the entire world. From digital elevation data, a computer can generate a shaded-relief image of the landscape by portraying the landscape as if it were illuminated from the northwest by the Sun (Figure 2-17). Although shaded relief maps have been drafted by hand in the past, one of the great virtues of a DEM is that the parameters of the image—such as its orientation, scale, and vertical exaggeration of the topography—can be readily manipulated. Further, various kinds of information or images can be overlain on the topography to create maps that were once impossible to conceive (for example, see Figure 2-29). Learning Check 2-8

How does a digital elevation model convey the topography of Earth’s surface?

GPS—THE GLOBAL POSITIONINGSYSTEM In recent decades, new electronic technologies have transformed map making. One such technology provides precise locational data for points on Earth’s surface. The Global Positioning System, or simply GPS, is a global navigation satellite system for determining accurate positions on or near Earth’s surface. It was developed in the 1970s and 1980s by the U.S. Department of Defense to aid in navigating aircraft, guiding missiles, and controlling ground troops. The first receivers were the size of a file cabinet, but continued technological improvement has reduced them to the size of a cell phone (Figure 2-18). In fact, increasingly devices such as portable computers, digital cameras, and cell phones contain built-in GPS receivers—revolutionizing both the way that data from field observations are gathered for use on maps and the way that data from maps can be retrieved in the field.

CHAPTER 2Portraying Earth43

▲Figure 2-18 A handheld GPS receiver. It receives signals sent by the

network of Global Positioning System satellites, calculating its position anywhere in the world to within 10 meters (33 feet).

The GPS system (formally called NAVSTAR GPS [Navigation Signal Timing and Ranging Global Positioning System]) is based on a constellation of at least 24 highaltitude satellites configured so that a minimum of four— and preferably six—are in view of any position on Earth (currently there are 31 active satellites, with several older satellites still in orbit as backups). Each satellite continuously transmits both identification and positioning information that can be picked up by receivers on Earth (Figure 2-19). The distance between a given receiver and each member in a group of four or more satellites is calculated by comparing clocks stored in both units, and then the three-dimensional coordinates of the receiver’s position are calculated through triangulation. The greater the number of channels in a GPS unit (even inexpensive units now have 12), the greater the number of satellites that can be tracked, and so the better the accuracy. The system already has accuracy greater than that of the best base maps. Even the simplest GPS units determine position to within 15 meters (49 feet). Wide Area Augmentation System (WAAS): Increased GPS accuracy is gained when the Wide Area Augmentation System (WAAS) is employed. Originally developed in cooperation with the Federal Aviation Administration (FAA) and the U.S. Department of Transportation, WAAS was implemented to increase the accuracy of instrument-based flight approaches for airplanes. Several dozen ground-based stations across North America monitor GPS signals from the satellites and then generate a correction message that is transmitted to GPS units. With WAAS, GPS units achieve a position accuracy of 3 meters

▲Figure 2-19 Global Positioning System (GPS) satellites circling 17,700

kilometers (11,000 miles) above Earth broadcast signals that are picked up by the receiver in an ambulance and used to pinpoint the location of the ambulance at any moment. A transmitter in the ambulance then sends this location information to a dispatch center. Knowing the location of all ambulances at any given moment, the dispatcher is able to route the closest available vehicle to each emergency and then direct that vehicle to the nearest appropriate health facility.

(about 10 feet) about 95 percent of the time. WAAS capability is built into virtually all new GPS receivers today. WAAS service is not yet available around the world, although similar systems are being implemented in Asia (Japan’s MultiFunctional Satellite Augmentation System) and Europe (the Euro Geostationary Navigation Overlay Service). Continuously Operating GPS Reference Stations (CORS):The National Oceanic and Atmospheric Administration (NOAA) manages a system of permanently installed GPS receiving stations known as Continuously Operating GPS Reference Stations (CORS). These highly accurate units are capable of detecting location differences of less than 1 centimeter of latitude, longitude, and elevation. They are used, for example, for the long-term monitoring of slight changes in the ground surface caused by lithospheric plate movement or the bulging of magma below a volcano. GPS Modernization Program:The United States has an ongoing modernization program for its GPS system. The upgrades already underway include replacing older satellites with newer ones that broadcast a second civilian GPS signal (known as “L2C”) that allows ionospheric

44Physical Geography: A Landscape Appreciation

correction to provide greater accuracy. Further improvements for civilian, aviation, and military use are also being implemented. GPS Applications:Since 1983, when access to GPS was made free to the public, astounding commercial growth has resulted. It is anticipated that eventually practically everything that moves in our society—airplane, truck, train, car, bus, ship, cell phone—will be equipped with a GPS receiver. Meanwhile, GPS has been employed in earthquake forecasting, ocean floor mapping, volcano monitoring, and a variety of mapping projects. For example, recognizing that GPS is a relatively inexpensive way of collecting data, the Federal Emergency Management Agency (FEMA) has used the system for damage assessment following such natural disasters as floods and hurricanes. GPS was used by workers to catalog items found in the enormous heaps of rubble at Ground Zero following the World Trade Center disaster of September 11, 2001. Commercial applications now far outnumber military uses of the system. The sale of GPS services is now a multibillion dollar a year industry in the United States. What was born as a military system has become a national economic resource. Because of the growing importance of GPS applications, other global navigation satellite systems are being implemented around the world. Russia’s GLONASS system is operational as of this writing, and Europe’s Galileo and China’s BeiDou (“Compass”) systems are under development. Decimal Form of Latitude & Longitude:In part because of the great accuracy of even inexpensive GPS units, latitude and longitude are increasingly being reported in decimal form, such as 94°45.5¿ W or even 94.7583° W rather than in its traditional form of 94°45¿30– W. Even the simplest handheld GPS units can provide location coordinates with a resolution of 0.01¿ (1/100th minute) or even 0.001¿ (1/1000th minute) of latitude and longitude (for reference, a difference in latitude of 0.001¿ represents a distance of less than 2 meters [about 6 feet]). Learning Check 2-9

How does GPS determine

locations on Earth?

REMOTE SENSING Throughout most of history, maps were the only tools available to depict anything more than a tiny portion of Earth’s surface with any degree of accuracy. However, sophisticated technology developed in recent years permits precision recording instruments to operate from highaltitude vantage points, providing a remarkable new set of tools for the study of Earth. Remote sensing refers to any measurement or acquisition of information by a recording device that is not in physical contact with the object under study—in this case, Earth’s surface.

Originally utilizing only airplanes, the use of satellites revolutionized remote sensing. We now have hundreds of satellites from dozens of countries perched high in the atmosphere where they either are circling Earth in a “low” orbit (an altitude of 20,000 kilometers [12,400 miles] or less) or in a lofty geosynchronous orbit (usually about 36,000 kilometers [22,400 miles] high) that allows a satellite to remain over the same spot on Earth at all times. These satellites gather data and produce images that provide communications, global positioning, weather data, and a variety of other information for a wide range of commercial and scientific applications—for example, see the box, “Focus: Using Remote Sensing Images to Study a Landscape.”

Aerial Photographs Aerial photography was almost the only Video Studying Fires form of remote sensing used for geoUsing Multiple graphic purposes until the 1960s. The earSatellite Sensors liest aerial photographs were taken from balloons in France in 1858 and in the United States in 1860. During World War I (1914–1918), systematic aerial photographic coverage from airplanes was possible. In World War II (1939–1945) color aerial photographs became important, and by this time photogrammetry—the science of obtaining reliable measurements and mapping from aerial photographs—had developed. Although satellite imagery has taken over the role of aerial photography for some applications, aerial photographs—now available in digital form from agencies such as the USGS—remain an important source of largescale geographic imagery. Orthophoto Maps:Orthophoto maps are multicolored, distortion-free photographic maps prepared from aerial photographs or digital images. Displacements caused by camera tilt or differences in terrain elevations have been removed, which gives the orthophoto the geometric characteristics of a map (Figure 2-20). Thus, an orthophoto can show the landscape in much greater detail than a conventional map, but retains the map characteristic of a common scale that allows precise measurement of distances. Orthophoto maps are particularly useful in flat-lying coastal areas because they can show subtle topographic detail in areas of very low relief, such as marshlands.

Visible Light and Infrared Sensing One of the most important advancements in remote sensing came when wavelengths of radiation other than visible light were first utilized. As we will see in Chapter 4, electromagnetic radiation includes a wide range of wavelengths of energy emitted by the Sun and other objects (Figure 2-21). The human eye (and conventional photographic film) is only sensitive to the narrow portion of the electromagnetic spectrum known as visible light—the colors seen in a rainbow. However, a wide range of other wavelengths of energy—such as X-rays, ultraviolet radiation, infrared radiation, and radio waves—are emitted, reflected, or

FOCUS

Using Remote Sensing Images to Study a Landscape ▶ Ryan

Jensen, Brigham Young University

R

emote sensing provides geographers and other researchers with a great amount of spatial information that can be analyzed to improve our understanding of landscapes. Geographers can study spatial features using data collected from both aerial platforms (airplanes or helicopters) and orbital platforms (satellites). Popular websites and programs provide much remote sensing data for anyone to examine at no cost. These programs, such as Google Earth™, MapQuest™, and the U.S. Geological Survey National Map, are valuable tools that display data at a variety of scales, depending on the “Zoom” level you select. Spatial resolution (the amount of detail you can see) becomes finer the further you zoom into a landscape. The usefulness of remote sensing will only increase as human activities and natural processes change Earth’s surface.

A Fluvial Landscape:

To see how remote sensing data can capture characteristics of Earth’s surface, look at the images of fluvial features (features formed by flowing water) in Figure 2-A. Landsat 5 acquired the data for the Costa Marques, Brazil, area in June 1984 and again in September 2001. Costa Marques is located along the Guapore/ Itenez River that forms the border between Brazil and Bolivia. Landsat data are typically acquired in 30 * 30 meter pixels. That is, each image pixel covers an area of 30 meters by 30 meters (98 feet by 98 feet), or 900 square meters

(9687 square feet) over a surface area of 180 kilometers by 180 kilometers (111 miles by 111 miles). In each of the images, you can see fluvial features such as meanders, meander scars, oxbow lakes, and floodplain lakes. The images can also be compared to study changes in the landscape. Notice that the rivers are much wider and there is more water on the floodplains in the 1984 scene than in the 2001 scene. Further, many of the oxbow lakes (Point A) had much more water in 1984 than in 2001. Meander scars that were very obvious in 1984 (Point B) are not as obvious in 2001. Sand that was not visible in 1984 (Point C) is visible in 2001. The 2001 image also shows evidence of human expansion in Costa Marques and along parts of the Guapore/Itenez River (Points D and E).

A More Detailed Look:

When more detail is needed, finer spatial resolution data may be used to study an area. Such data are available from commercial

B F

▲ Figure 2-B Fine-spatial resolution data showing a meander neck and meander scars in the Costa Marques area. September 2001

June 1984

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C

B

websites and programs such as Google Earth, MapQuest, and many others. For example, look at Point F in Figure 2-A. It is reasonable to assume that the river at that point will eventually create a new channel across the neck of the meander. This process cannot be clearly examined using the 30 * 30 meter Landsat data, but it can be examined using finer-resolution data. Figure 2-B shows a more-detailed image of the same meander neck at Point F. As you can see, there might be evidence of a new channel forming at Point F. In fact, in wet years, river water may flow through the meander neck. Consider another example: Point B in Figure 2-B shows the same meander scars as the Landsat images in Figure 2-A (Point B). These features can be more fully examined using the detailed image in Google Earth, which can also be used to make measurements such as length and area. Knowing the area of the lake within the scar might be useful in determining how the lake changes from season to season or year to year.

B

A F

Costa Marques

Guapore/Itenez River

C

A F

E

◀ Figure 2-A Two Landsat images acquired over the Costa Marques, Brazil, area in 1984 and 2001.

45

CA

one of the major uses of color IR imagery remains the identification and evaluation of vegetation (Figure 2-22).

74

PE

Thermal Infrared Sensing

FEAR

None of the middle or far infrared part of the electromagnetic spectrum, called thermal infrared (thermal IR), can be sensed with conventional digital cameras or traditional photographic film; as a result, special supercooled scanners are needed. Thermal scanning measures the radiant temperature of objects and may be carried out either day or night. The photograph-like images produced in this process are particularly useful for showing diurnal temperature differences between land and water, and between bedrock and alluvium, for studying thermal water pollution, and for detecting forest fires. By far the greatest use of thermal IR scanning systems has been on meteorological satellites (for example, see “Focus: GOES Weather Satellites,” in Chapter 6). Although the spatial resolution (the size of the smallest feature that can be identified) is not as high as some other kinds of sensing systems, it is more than sufficient to provide details that allow weather forecasting that is far more accurate and complete than ever before.

RIVE

R

17

▲Figure 2-20 Orthophoto map of Wilmington, North Carolina; original

scale: 1:24,000.

absorbed by surfaces and can be detected by special films or instruments, yielding a wealth of information about the environment. Color infrared (color IR) imagery uses electronic sensors or photographic film sensitive to radiation in the near infrared portion of the electromagnetic spectrum— wavelengths of radiation just longer than the human eye can see. With color IR imagery, sensitivity to visible blue light is replaced by sensitivity to near infrared wavelengths. The images produced in this way, even though they are “false-color” images (e.g., living vegetation appears red instead of green), are still extremely valuable. Color IR film was first widely used in World War II when it was often called “camouflage-detection” film because of its ability to discriminate living vegetation from the withering vegetation used to hide objects during the war. Today,

400

Nanometers 500 600

Learning Check 2-10

What are the differences between “near infrared” and “thermal infrared” images, and what kinds of features might be studied with each?

Multispectral Remote Sensing Today, most sophisticated remote sensing satellites are multispectral or multiband (the various regions of the electromagnetic spectrum are sometimes called bands). These instruments detect and record many bands of the electromagnetic spectrum simultaneously. Thus, although traditional photographic film was sensitive to only a narrow band of visible radiation, a satellite equipped with a multiband instrument images the surface of Earth in several spectrum

Microwave FM VHF UHF

AM

VLF

Radio

700 Infrared 100 GHz 1 GHz Near Far 1 100 Microns

Visible Ultraviolet Far Near X-rays “Hard” “Soft”

◀Figure 2-21 The electromagnetic

Gamma rays

10–14

46

10–12

10–10

10–8

10–6 10–4 10–2 Wavelength (meters)

1

102

104

spectrum. The human eye can only sense radiation from the visible-light region. Conventional photography also can use only a small portion of the total spectrum. Various specialized remote-sensing scanners are capable of “seeing” radiation from other parts of the spectrum.

CHAPTER 2Portraying Earth47

regions at once—visible light, near infrared, middle infrared and thermal infrared—each useful for different applications. A multispectral satellite image is digital, conveyed through a matrix of numbers, with each number representing a single value for a specific pixel (picture element) and band. These data are stored in the satellite, eventually transmitted to an Earth receiving station, numerically processed by a computer, and produced as a set of gray values and/or colors on a screen or hard-copy printout (Figure 2-23).

▲Figure 2-22 Color infrared image from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) of the cities ofPalm Springs, Cathedral City, and Palm Desert, California. In this false-color infrared image, healthy vegetation is shown in red; bare ground is shown in gray-blue.

Landsat:The early NASA space missions (Mercury, Gemini, and Apollo) used multiband photography obtained through multicamera arrays. These imaging experiments were so successful that NASA then developed what was initially called the Earth Resources Technology Satellite series (ERTS) and later renamed Landsat. The 1970s and 1980s saw the launch of five Landsat satellites carrying a variety of sensor systems. Landsat 7, which was launched in 1999, carries an instrument array called the Enhanced Thematic Mapper Plus that provides images in eight spectral bands with a resolution of 15 meters (49 feet) in the panchromatic band (sensitive to visible and near infrared wavelengths), 30 meters (98 feet) in the six narrow bands of visible and short infrared wavelengths, and 60 meters (197 feet) in thermal infrared (Figure 2-24). A description of the primary applications for the various bands is provided in Table 2-1. Although the satellite was originally designed for a life of less than 10 years, as of this writing Landsat 7 remains in active operation. The

30 meters

30-meter resolution

Image stored in satellite as matrix of digital values

Band 1 – Blue-green Band 2 – Green Band 3 – Red Band 4 – Near IR Band 5 – Mid-IR Band 6 – Thermal IR Band 7 – Mid-IR

Computer manipulation and enhancement of data

The “digital” image ▲Figure 2-23 The sequence of events that takes place as a multispectral satellite scan is converted to a digital image.

Satellite receiver on Earth

Lake Ontario

New York

Pennsylvania d Islan Long

New Jersey

ATLANTIC OCEAN

▲Figure 2-24 Landsat 7 satellite image of the island of Jeju-do, South

Korea, taken with the Enhanced Thematic Mapper Plus in April 2000. The central shield volcano of Mount Halla rises to an elevation of 1950 meters(6398 ft). The provincial capital city of Jeju City is the gray patch along the northern shore. Note the subtle differences in the color of the water around the island.

next-generation Landsat satellite, known as the Landsat Data Continuity Mission, is scheduled for launch in 2013. Earth Observing System Satellites:In 1999 NASA launched the first of its Earth Observing System (EOS) satellites known as Terra. The key instrument of these satellites is the Moderate Resolution Imaging Spectroradiometer (MODIS), which gathers data in 36 spectral bands (Figure2-25) and provides images covering the entire planet every one to two days. Other devices onboard Terra include the Clouds and the Earth’s Radiant Energy System (CERES) instruments for monitoring the energy balance of Earth, and the Multiangle Image Spectroradiometer (MISR) capable of distinguishing various types of atmospheric particulates, land surfaces, and cloud forms—with special processing, three-dimensional models of image data are possible. The more recently launched EOS satellite, Aqua, is designed to enhance our understanding of Earth’s water cycle by monitoring water vapor, clouds, precipitation, glaciers, and soil wetness. In addition to instruments

TABLE 2-1

▲Figure 2-25 Natural color satellite image showing the northeastern

United States after an early season heavy snowstorm. This image was taken on October 30, 2011, with the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument aboard NASA’s Terra satellite.

such as MODIS, Aqua includes the Atmospheric Infrared Sounder (AIRS), designed to permit very accurate temperature measurements throughout the atmosphere. In June 2011, NASA launched an Argentine-built satellite that included an instrument called Aquarius that enables scientists to monitor concentrations of dissolved salts near the surface of the ocean (see Figure 9-6)— improving our understanding of the effects of long-term climate change and short-term phenomena such as El Niño (discussed in Chapter 5). Many satellite images are now easily available for viewing and downloading via the Internet from NASA and NOAA. For example, you can visit http://earthobservatory. nasa.gov/ and http://www.goes.noaa.gov/. Commercial High-Resolution Satellites:In addition to imagery from government-operated satellites that is often available either free of charge or for a nominal fee (such as the GOES satellites, Landsat, and the EOS satellites), a number of satellites now offer very high-resolution

Bands of the Landsat 7 Enhanced Thematic Mapper Plus

Band Number

Bandwidth (micrometers)

Spectral Region

Resolution (meters)

Applications

1

0.45–0.52

Blue

30

Water penetration and vegetation analysis

2

0.52–0.60

Green

30

Vegetation analysis

3

0.63–0.69

Red

30

Vegetation analysis

4

0.77–0.90

Near IR

30

Biomass and soil analysis

5

1.55–1.75

Middle IR

30

Soil moisture and hydrologic analysis

6

10.4–12.5

Thermal

60

Geothermal resources and vegetation stress

7

2.08–2.35

Middle IR

30

Geologic features

8

0.52–0.90

Panchromatic

15

High-resolution images

48

CHAPTER 2Portraying Earth49

imagery (up to 50- to 60-centimeter [20 to 24 in.] resolution) for commercial applications, including SPOT (Satellite Pour l’Observation de la Terre), GeoEye-1, QuickBird, and WorldView. The market for these images seems to be growing remarkably. Learning Check 2-11

What is “multispectral”

remote sensing?

Radar and Sonar Sensing:All the systems mentioned so far work by sensing the natural radiation emitted by or reflected from an object and are therefore characterized as passive systems. Another type of system, called an active system, has its own source of electromagnetic radiation. The most important active sensing system used in the Earth sciences is radar, the acronym for radio detection and ranging. Radar senses wavelengths longer than 1 millimeter, using the principle that the time it takes for an emitted signal to reach a target and then return to the sender can be converted to distance information. Initially, radar images were viewed only on a screen, but they are now available in photograph-like form (Figure2-26). In common with some other sensors, radar is capable of operating by day or night, but it is unique in ▼Figure 2-26 Radar image showing the topography of the island of

Ireland. The data were gathered from the Shuttle Radar Topography Mission using synthetic aperture radar aboard Space Shuttle Endeavour in 2000. The data were processed with elevations represented by different colors, ranging from green for lowlands to white for high mountaintops. Shaded relief was added to highlight the topography.

its ability to penetrate atmospheric moisture. Thus, some wet tropical areas that could never be sensed by other systems have now been imaged by radar. Radar imagery is particularly useful for terrain analysis in places of frequent cloud cover or thick vegetation, and for meteorology— especially in the real-time study and mapping of rainfall and severe weather (the use of specialized Doppler radar in meteorology is discussed in Chapter 7). Another active remote sensing system, sonar (sound navigation and ranging), permits underwater imaging so that scientists can determine the form of that part of Earth’s crust hidden by the world ocean.

GEOGRAPHIC INFORMATION SYSTEMS (GIS) Cartographers have been at work since the days of the early Egyptians, but it was only with the introduction of computers in the 1950s that their technology has advanced beyond manual drawing on a piece of paper. Computers have provided incredible improvements in speed and image handling ability—as one example, all of the maps in this textbook were made with desktop computers. Of all the technological advances in cartography over the last few decades, however, one of the most revolutionary has been geographic information systems. Geographic Information Systems (GIS):Geographic information systems—commonly called simply GIS—are computer systems designed to analyze and display spatial data. GIS involves specialized hardware and software that allow users to collect, store, retrieve, reorganize, analyze, and map geographic data from the real world (Figure 2-27). Geographic information systems originally developed out of computer science, geography, and cartography, and they found their greatest early uses in surveying, photogrammetry, spatial statistics, and remote sensing. So commonly are they now used in geographical analysis that GIS has become a science of spatial analysis by itself, known as geographic information science, and the software has spun off a multibillion-dollar industry in spatial data and spatial information. Geographic information systems are libraries of information that use maps to organize, store, view, and analyze information in an intuitive, visual manner. Just as an ordinary computer database management system can manipulate rows and columns of data in tabular form, a GIS allows data management using the link between data and a map. This means that the map and data are encoded, usually as numbers representing coordinates of locations at points on a grid covering the mapped area. Once the data and the map are inside the GIS, the user can organize or search the data using the map, or the map using the data. An important attribute is the capability of GIS data from different maps and sources, such as field data, map data, and remotely sensed images, to be registered together at the correct geographic location within a common

50Physical Geography: A Landscape Appreciation

1951

1985

0 0

5 5

2005

10 Miles 10 Kilometers

Vermont

▲Figure 2-27 Land use changes on Cape Cod from 1951 to 2005, showing the

expansion of residential housing and the accompanying loss of forest. Dark green shows areas of forest, yellow shows areas of residential housing, and red shows areas of commercial and industrial development.

New Hampshire

Massachusetts New York Connecticut

Rhode Island 0 0

database, with a common map scale and map projection. In this way, one map layer, such as the locations of rivers, can then be cross-referenced to another, such as geology, soils, or slope. Overlay Analysis:GIS is frequently used in overlay analysis, where two or more layers of data are superimposed or integrated. GIS treats each spatially distributed variable as a particular layer in a sequence of overlays. As shown in Figure 2-28, input layers bring together such diverse elements as topography, vegetation, land use, land ownership, and land survey. Details of these various components are converted to digital data and are synthesized onto a reference map or data set. Particularly useful images for the study of physical geography can be developed with GIS when data or satellite images are overlain on topography generated with a digital elevation model, offering oblique views of the landscape previously impossible to obtain (Figure 2-29). Geographic information systems are used today in a diverse array of applications concerned with geographic location. Because they provide impressive output maps and a powerful methodology for analytical studies, GIS can bring a new and more complete perspective to resource management, environmental monitoring, natural hazards assessment—and a host of other fields. The growth of GIS is so rapid today that there are few fields of academic study, sectors of the economy, and divisions of government not using these powerful tools. Learning Check 2-12 fromGPS?

How is GIS different

25 25

50 Miles 50 Kilometers

Grid

Surv

ey

Remotely sensed image Zoning Floodplains Wetlands Land cover Soils Survey control Composite overlay

Fina

l Ma

p

▲Figure 2-28 Much GIS work involves layers of spatial data

superimposed upon one another.

Tools of the Geographer As we have just seen, a vast array of maps, remotely sensed imagery, satellite data, and GIS applications are now available, making the tools of the geographer more widely used than ever before. The effective use of these tools, however,

CHAPTER 2Portraying Earth51

▲Figure 2-29 This oblique view of Bangladesh and the Himalayas

was created by configuring MODIS images from the Terra satellite over a 50-times vertically exaggerated digital elevation model of the topography.

still entails thoughtful consideration. Although it is easy to download a satellite image or quickly print a handsomelooking map from the Internet, those images and maps may or may not be useful for analysis—and might actually be deceptive—unless care is taken to choose an appropriate map projection, an appropriate scale, and an appropriate selection of data to depict. Choosing Effective Maps and Imagery:Certain types of imagery are useful for particular purposes.

Forexample, when studying major features of the lithosphere, high-altitude space imagery is especially valuable (Figure2-30), although this type of imagery might have limited use in detailed local terrain studies where largescale oblique aerial photographs or topographic maps might be more appropriate. For studying the hydrosphere, multiband satellite images of an entire hemisphere can tell us much about the water content in clouds, air masses, glaciers, and snowfields at a given time, although detailed conventional color images might be better for discriminating complicated shoreline features. Vegetation patterns in the biosphere are often best appreciated with color infrared imagery—overall vegetation patterns on small-scale satellite images and detailed aerial photographs for crop and forest inventory studies. Features of human creation are generally not evident on very highaltitude imagery, but they become increasingly clear as one approaches Earth, and so survey patterns, transportation lines, rural settlements, and cities are best interpreted on imagery of intermediate or large scale. And in all cases, GIS may be used to uncover or highlight geographic relationships that may not be obvious when employing any single source of data or kind of imagery. In using these tools, the geographer should never lose sight of our major objective: to better understand Earth. Such understanding does not come simply through the application of technology, however. Understanding comes from a carefully designed investigation, often using technology, but frequently supported by such traditional sources of information as field study and observation. ◀Figure 2-30 Natural

color satellite image of the Yukon River Delta, Alaska, taken with the Enhanced Thematic Mapper Plus on Landsat 7.

52Physical Geography: A Landscape Appreciation

Chapter 2

LEARNING REVIEW After studying this chapter, you should be able to answer the following questions. Key terms from each text section are shown in bold type. Definitions for key terms are also found in the glossary at the back of the book.

KEY TERMS AND CONCEPTS Maps and Globes (p. 31) 1. How is a map different from a globe? 2. Why is it impossible for a map of the world to portray Earth as accurately as can be done with a globe?

Map Scale (p. 33) 3. Describe and explain the concept of map scale. 4. Contrast graphic map scales, fractional map scales, and verbal map scales. 5. What is meant by a map scale with a representative fraction of 1/100,000 (also written 1:100,000)? 6. Explain the difference between large-scale maps and small-scale maps.

13. What is a loxodrome (rhumb line)?

Conveying Information on Maps (p. 39) 14. Explain the concept of isolines. 15. What characteristics on maps are shown by isotherms, isobars, and elevation contour lines? 16. How does a digital elevation model (DEM) depict the landscape?

GPS—The Global Positioning System (p. 42) 17. Briefly explain how the Global Positioning System (GPS) works.

Remote Sensing (p. 44) Map Projections and Map Properties (p. 35) 7. What is meant by a map projection? 8. Explain the differences between an equivalent (equal area) map projection and a conformal map projection. 9. Is it possible for a map to be both conformal and equivalent? 10. What is a compromise map projection?

Families of Map Projections (p. 36) 11. Briefly describe the four major families of map projections: cylindrical projections, planar projections, conic projections, and pseudocylindrical projections. 12. Why is a Mercator projection useful as a navigationmap? Why is it not ideal for use as a general purpose map?

18. What is remote sensing? 19. Briefly define the following terms: aerial photograph, photogrammetry, orthophoto map. 20. What are some of the applications of color infrared imagery? 21. What are some of the applications of thermal infrared imagery? 22. Describe multispectral remote sensing. 23. Compare and contrast radar and sonar?

Geographic Information Systems (GIS) (p. 49) 24. Distinguish between GPS and GIS (geographic information systems).

STUDY QUESTIONS 1. Why are there so many types of map projections? 2. What kind of map projection would be best for studying changes in the amount of permafrost in the Arctic? Why? Consider both the general family of projection, and its properties such as equivalence and conformality. 3. Look at Figure 1-31, the world map of time zones shown in Chapter 1: a. Is this map an equivalent, conformal, or compromise projection? How can you tell? b. In which of the four families of map projections does it belong? How can you tell?

4. Isolines never just start or stop on a map—every isoline must close on itself, either on or off the map. Why? 5. A GPS receiver in your car simply calculates your current latitude and longitude. How can it use this basic locational data to determine your speed and direction of travel? 6. Describe one kind of application where radar imagery may be useful for geographical analysis. Explain the advantages of radar over other kinds of remote sensing in your example.

CHAPTER 2Portraying Earth53

EXERCISES 1. On a map with a fractional scale of 1:24,000 a. One inch represents how many feet? _________ b. One centimeter represents how many meters? _________ c. If the map is 18 inches wide and 22 inches tall, how many square miles are shown on the map? _________ 2. If we construct a globe at a scale of 1:1,000,000, what will be its diameter? (You may give your answer in either feet or meters.) 3. Convert the following latitude and longitude coordinates presented in decimal form (as might be

shown on a GPS unit) into their conventional form of degrees/minutes/seconds: 42.6700° N = _________° _________¿ _________– N 105.2250° W = _________° _________¿ _________– W 4. Convert the following latitude and longitude coordinates from their conventional form of degrees/ minutes/seconds into decimal form: 22°20¿15– N = _________° N 137°30¿45– E = _________° E

Seeing Geographically Look again at the image of Baja at the beginning of the chapter (p. 30). The Baja peninsula is about 160 kilometers (100 miles) wide in the north and about 80 kilometers (50 miles) wide at its southern tip. About how far has the dust blown to the west off of Baja? In what part of the image is the shape of the land least distorted? Most distorted? Could a single graphic map scale be used to accurately measure distances everywhere on this image? Why or why not?

Looking for additional review and test prep materials? Visit the Study Area in MasteringGeography™ to enhance your geographic literacy, spatial reasoning skills, and understanding of this chapter’s content by accessing a variety of resources, including geoscience animations, interactive maps, videos, RSS feeds, flashcards, web links, self-study quizzes, and an eText version of McKnight’s Physical Geography: A Landscape Appreciation.

Chapter 3

INTRODUCTION TO THE ATMOSPHERE

EARTH IS DIFFERENT FROM ALL OTHER KNOWN PLANETS IN A variety of ways. One of the most notable differences is the presence around our planet of an atmosphere distinctive from other planetary atmospheres. It is our atmosphere that makes life possible on Earth. The atmosphere supplies most of the oxygen that animals must have to survive, as well as the carbon dioxide needed by plants. It helps maintain a water supply, which is essential to all living things. It insulates Earth’s surface against temperature extremes and thus provides a livable environment over most of the planet. It also shields Earth from much of the Sun’s ultraviolet radiation, which otherwise would be damaging to most life forms. The atmosphere is a complex and dynamic system. This chapter provides a foundation for understanding the atmosphere and the patterns and processes of weather and climate. Here we describe the composition and structure of the atmosphere, the basic elements or “ingredients” of weather and climate, and the most important “controls” or influences of weather and climate. As you study this chapter, think about these key questions: S What major gases are found in the atmosphere, and what roles do small concentra-

tions of variable gases and impurities play in weather and climate? S What are the characteristics and significance of the various layers of the atmosphere,

especially the troposphere? S In what ways have humans altered the composition of the atmosphere, such as by

releasing chemicals that deplete the ozone layer or by releasing other types of air pollution? S What is the difference between “weather” and “climate,” and what are the four

elements of weather and climate and the seven most important controls of weather and climate?

SIZE AND COMPOSITION OF THE ATMOSPHERE Air—generally used as a synonym for atmosphere—is not a specific gas, but rather a mixture of gases, mainly nitrogen and oxygen. It often contains small quantities of tiny solid and liquid particles held in suspension in the air, as well as varying amounts of gaseous impurities. Pure air is odorless, tasteless, and invisible. Gaseous impurities, on the other hand, can often be smelled, and the air may even become visible if enough microscopic solid and liquid impurities coalesce (stick together) to form particles large enough to either reflect or scatter sunlight. Clouds, by far the most conspicuous visible features of the atmosphere, represent the coalescing of water droplets or ice crystals around microscopic particles that act as condensation nuclei.

Seeing Geographically This view looking west over the Gulf of St. Lawrence toward the Gaspé Peninsula in Canada was taken from the International Space Station. How thick does the visible part of the atmosphere appear in relation to the size of Earth itself? Where does the layer of clouds appear to be in relation to the overall thickness of the atmosphere? 55

56Physical Geography: A Landscape Appreciation

Size of Earth’s Atmosphere The atmosphere completely surrounds Earth and can be thought of as a vast ocean of air, with Earth at its bottom (Figure 3-1). It is held to Earth by gravitational attraction and therefore accompanies our planet in all its celestial motions. The attachment of Earth and atmosphere is a loose one, however, and the atmosphere can therefore move on its own, doing things that the solid Earth cannot do. Density Decrease with Altitude:Although the atmosphere extends outward at least 10,000 kilometers (6000 miles), most of its mass is concentrated at very low altitudes. More than half of the mass of the atmosphere lies below the summit of North America’s highest peak, Mount McKinley (Denali) in Alaska, which reaches an elevation of 6.2 kilometers (3.8 miles), and more than 98 percent of it lies within 26 kilometers (16 miles) of sea level (Figure 3-2). Therefore, relative to Earth’s diameter of about 13,000 kilometers (8000 miles), the “ocean of air” we live in is a very shallow one. In addition to reaching upward above Earth’s surface, the atmosphere also extends slightly downward. Because air expands to fill empty spaces, it penetrates into caves and crevices in rocks and soil. Moreover, it is dissolved in the waters of Earth and in the bloodstreams of organisms. The atmosphere interacts with other components of Earth’s environment, and it is instrumental in providing a hospitable setting for life. Whereas we often speak of human beings as creatures of Earth, it is perhaps more accurate to consider ourselves creatures of the atmosphere. As surely as a crab crawling on the sea bottom is a resident of the ocean, a person living at the bottom of the ocean of air is a resident of the atmosphere.

26 km (16 miles)

48% of atmospheric mass

Mt. McKinley 6.19 km (20,320 feet) 6 km (3.8 miles) 50% of atmospheric mass Sea level ▲Figure 3-2 Most of the atmospheric mass is close to Earth’s surface.

More than half of the mass is below the highest point of Mount McKinley (Denali), North America’s highest peak.

Learning Check 3-1

What generally happens to the density of the atmosphere with increasing altitude? (Answer on p. AK-1)

▼Figure 3-1 The atmosphere completely surrounds Earth in this composite

satellite image; beyond the narrow blue band of the atmosphere is the blackness of outer space.

Development of Earth’s Modern Atmosphere The atmosphere today is very different from what it was during the early history of Earth. Shortly after Earth formed about 4.6 billion years ago, the atmosphere probably consisted mostly of light elements such as hydrogen and helium. By perhaps 4 billion years ago, this ancient atmosphere was changing as those light gases were being lost and as outgassing from volcanic eruptions added large amounts of carbon dioxide and water vapor, along with small amounts of other gases such as nitrogen. It is likely that arriving comets also contributed water to Earth’s atmosphere. As ancient Earth cooled, most of the water vapor condensed out of the atmosphere, forming the world ocean. By about 3.5 billion years ago, early forms of life—such as bacteria that could survive without oxygen—were beginning to remove carbon dioxide and release oxygen into the atmosphere. Over time, oceanic and terrestrial plants continued the transformation from a carbon dioxide-rich to an oxygen-rich atmosphere through the process of photosynthesis (photosynthesis is discussed in Chapter 10). Our modern atmosphere, therefore, was significantly influenced by life on Earth.

CHAPTER 3Introduction to the Atmosphere57

Composition of the Modern Atmosphere The chemical composition of pure, dry air at lower altitudes (altitudes lower than about 80 kilometers or 50 miles) is simple and uniform, and the concentrations of the major components—the permanent gases—are essentially unvarying over time. However, certain minor gases and nongaseous particles—the variable gases and particulates—vary markedly from place to place or from time to time, as does the amount of moisture in the air.

The remaining 1 percent of the atmosphere’s volume consists mostly of the inert gas argon. These three principal atmospheric gases—nitrogen, oxygen, argon—have a minimal effect on weather and climate and therefore need no further consideration here. The trace gases—neon, helium, krypton, and hydrogen—also have little effect on weather and climate.

Variable Gases

Permanent Gases

Several other gases occur in sparse but highly variable quantities in the atmosphere, but their influence on weather and climate is significant.

Nitrogen and Oxygen:The two most abundant gases in the atmosphere are nitrogen and oxygen (Figure 3-3). Nitrogen makes up more than 78 percent of the total, and oxygen makes up nearly 21 percent. Nitrogen is added to the air by the decay and burning of organic matter, volcanic eruptions, and the chemical breakdown of certain rocks, and it is removed by certain biological processes and by being washed out of the atmosphere in rain or snow. Overall, the addition and removal of nitrogen gas are balanced, and consequently the quantity present in the air remains constant over time. Oxygen is produced by vegetation and is removed by a variety of organic and inorganic processes; its total quantity also apparently remains stable.

Water Vapor:Water in the form of a gas is known as water vapor. Water vapor is invisible—the visible forms of water in the atmosphere, such as clouds and precipitation, consist of water in its liquid or solid form (ice). Water vapor is most abundant in air overlying warm, moist surface areas such as tropical oceans, where water vapor may amount to as much as 4 percent of total volume. Over deserts and in polar regions, the amount of water vapor is but a tiny fraction of 1 percent. In the atmosphere as a whole, the total amount of water vapor remains nearly constant. Thus, its listing as a “variable gas” in Figure 3-3 means variable in location. Water vapor has a significant effect on weather and climate: it is

Carbon dioxide (CO2) 0.0395% Argon (Ar) 0.93%

All other gases

Permanent Neon (Ne) Helium (He) Krypton (Kr) Hydrogen (H2) Variable Water vapor (H2O) Methane (CH4) Ozone (O3)

Percent by volume 0.00182 0.00052 0.00011 0.00005

Concentration in parts per million 18.2 5.2 1.1 0.5

0 to about 4 0.00018

Oxygen (O2) 20.95%

Nitrogen (N2) 78.08%

▲Figure 3-3 Proportional volume of the gases in the atmosphere. Nitrogen and oxygen are the

dominant components. Although found in tiny amounts, some variable gases play important roles in atmospheric processes.

— 1.8 600 cm (240")

OCEAN 0 0

15 15

30 Miles 30 Kilometers

consider one additional control of weather and climate— or perhaps more correctly, a control of some of the controls of weather and climate—the rotation of Earth. Learning Check 3-8

Puako annual rainfall = 23 cm (9 inches)

19˚N

British Isles is counterpointed by localized thunderstorms over North Africa, Sicily, Italy, and Greece.

155˚W

PA C I F I C OCEAN

20˚N

▲Figure 3-22 A prominent midlatitude cyclone storm system over the

60 in >152 cm

40–60 in 102–152 cm

25–40 in 63–102 cm

15–25 in 38–63 cm

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