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Glaciers, Sea Ice, and Ice Formation (Dynamic Earth)

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Glaciers, Sea Ice, and Ice Formation (Dynamic Earth) Published in 2011 by Britannica Educational Publishing (a trademark of Encyclopædia Britannica, Inc.) in association with Rosen Educational Services, LLC 29 East 21st Street, New York, NY 10010. Copyright © 2011 Encyclopædia Britannica, Inc. Britannica, Encyclopædia Britannica, and the Thistle logo are registered trademarks of Encyclopædia Britannica, Inc. All rights reserved. Rosen Educational Services materials copyright © 2011 Rosen Educational Services, LLC. All rights reserved. Distributed exclusively by Rosen Educational Services. For a listing of additional Britannica Educational Publishing titles, call toll free (800) 237-9932. First Edition Britannica Educational Publishing Michael I. Levy: Executive Editor J.E. Luebering: Senior Manager Marilyn L. Barton: Senior Coordinator, Production Control Steven Bosco: Director, Editorial Technologies Lisa S. Braucher: Senior Producer and Data Editor Yvette Charboneau: Senior Copy Editor Kathy Nakamura: Manager, Media Acquisition John P. Rafferty: Associate Editor, Earth Sciences Rosen Educational Services Jeanne Nagle: Editor Nelson Sá: Art Director Cindy Reiman: Photography Manager Matthew Cauli: Designer, Cover Design Introduction by Theresa Shea Library of Congress Cataloging-in-Publication Data Glaciers, sea ice, and ice formation / edited by John P. Rafferty.—1st ed. p. cm.—(Dynamic earth) “In association with Britannica Educational Publishing, Rosen Educational Services.” Includes bibliographical references and index. ISBN 978-1-61530-189-8 (eBook) 1. Glaciers. 2. Sea ice. 3. Ice. I. Rafferty, John P. II. Series: Dynamic earth. GB2403.2.G54 2010 551.31—dc22 2010000226 On the cover: The Vatnajokull glacier in Iceland’s Jokulsarlon Glacier Lake. Michele Falzone/ Photographer's Choice/Getty Images On page 12: The San Rafael glacier in Chile, c. 1950. Three Lions/Hulton Archive/Getty Images On pages 20,226, 232, 235, 246: Ice melting in Lake Baikal, located in southeast Siberia. Shutterstock.com Pages 21, 29, 53, 74, 116, 145, 182 © www.istockphoto.com/Pablo Caridad CONTENTS Introduction 12 Chapter 1: Ice on Planet Earth 21 30 The Water Molecule 21 The Ice Crystal 23 Hoarfrost and Rime 24 Mechanical Properties 25 Thermal Properties 26 Optical Properties 27 Electromagnetic Properties 27 Ice Ages 28 Chapter 2: Permafrost 29 The Origin and Stability of Permafrost 30 Air Temperature and Ground Temperature 31 Climatic Change 32 Permafrost Distribution In the Northern Hemisphere 33 The Local Thickness of Permafrost 34 The Eff ects of Climate 35 37 The Eff ects of Water Bodies 35 The Eff ects of Solar Radiation, Vegetation, and Snow Cover 36 Types of Ground Ice 37 Ice Wedges 39 Active Wedges, 4425 Inactive Wedges, and Ice-Wedge Casts 40 Surface Manifestations of Permafrost and Seasonally Frozen Ground 41 Polygonal Ground 42 Thermokarst Formations 43 Pingos 44 Patterned Ground 45 Soil Flow 46 The Study of Permafrost 47 Problems Posed by 2551 Permafrost 48 Permafrost Engineering 48 Development in Permafrost Areas 50 Chapter 3: Ice in Lakes and Rivers 53 The Seasonal Cycle 53 Ice Formation in Lakes 54 Nucleation of Ice Crystals 56 The Eff ects of Wind Mixing 57 5625 The Rates of Growth 58 Variations in Ice Structure 60 Ice Decay 61 Thinning and Rotting 61 Melting 62 The Geographic Distribution of Lake Ice 63 Ice Formation in Rivers 64 Accumulating Ice Cover 65 Growth of Fixed Ice Cover 67 Ice Buildups 67 6825 Decay and Ice Jams 69 72 River Ice Modifi cation 70 The Geographic Distribution of River Ice 72 Chapter 4: Glaciers and Ice Sheets 74 The Formation and Characteristics of Glacier Ice 76 Mass Balance 78 Heat or Energy Balance 80 Glacier Flow 81 Mountain Glaciers and Other 91 Smaller Ice Masses 84 Classifi cation of Mountain Glaciers 84 Surface Features 86 Mass Balance of Mountain Glaciers 88 The Flow of Mountain Glaciers 90 Crevasse 91 Glacier Hydrology 92 Glacier Floods 93 100 Glacier Surges 94 Tidewater Glaciers 95 Rock Glacier 96 The Great Ice Sheets 97 The Antarctic Ice Sheet 97 The Greenland Ice Sheet 99 Accumulation and Ablation of the Ice Sheets 102 Net Mass Balance 105 The Flow of the Ice Sheets 107 Ross Ice Shelf 108 110 The Information from 11725 Deep Cores 110 The Response of Glaciers to Climatic Change 113 Glaciers and Sea Level 114 Chapter 5: Glacial Landforms 116 General Considerations 116 Glaciers and Topography 116 Glacial Erosion 118 Glacial Deposition 121 Erosional Landforms 124 12325 Small-Scale Features of Glacial Erosion 124 Rock Polish 124 Striations 125 P-Forms and Glacial Grooves 126 The Erosional Landforms of Valley Glaciers 126 Cirques, Tarns, U-shaped Valleys, Arêtes, and Horns 127 12825 Hanging Valleys 130 Paternoster Lakes 130 Roches Moutonnées 131 Rock Drumlins 131 The Erosional Landforms of Continental Glaciers 131 Depositional Landforms 135 The Depositional Landforms of Valley Glaciers 136 Moraines 136 13325 Flutes 137 The Depositional Landforms of 149 Continental Glaciers 137 Meltwater Deposits 138 Glaciofl uvial Deposits 139 Glaciolacustrine Deposits 141 Periglacial Landforms 143 Felsenmeers, Talus, and Rock Glaciers 143 Chapter 6: Icebergs and Sea Ice 145 155 Icebergs 145 The Origin of Antarctic Icebergs 145 The Origin of Arctic Icebergs 148 Iceberg Structure 150 Iceberg Size and Shape 153 Erosion and Melting 155 The Distribution of Icebergs and Their Drift 159 Trajectories 157 Iceberg Scour and Sediment Transport 162 The Climatic Impacts of Icebergs 165 The Impacts on Ice Sheets and Sea Level 165 The Impact on Ocean Structure 166 Iceberg Detection, Tracking, and 174 Management 168 Sea Ice 170 Ice Salinity, Temperature, 178 and Ecological Interactions 171 Sea Ice Formation and Features 172 Pack Ice Drift and Thickness 176 Sea Ice and its Interactions with the Oceans, Atmosphere, and Climate 177 The Emerging Impacts 185 of Recent Changes to Sea Ice 179 Chapter 7: The Arctic and Antarctic 182 The Arctic 182 Continental Ice Sheets of the Past 183 Terrain 186 Drainage and Soils 189 Present-Day Glaciation 191 194 Glacier Groups 193 Climate 196 The Arctic Ocean 201 Oceanography 202 Sea Ice in the Arctic Ocean 206 Antarctica 208 Physical Features 211 Antarctic Glaciation 213 The Surrounding Seas 217 Climate 220 209 The Power of Ice 224 Appendix: Significant Glaciers, Ice Sheets, and Ice Shelves 226 Amery Ice Shelf 226 Beardmore Glacier 226 Filchner Ice Shelf 227 Larsen Ice Shelf 227 Laurentide Ice Sheet 228 Ronne Ice Shelf 229 Shackleton Ice Shelf 229 Skelton Glacier 230 Wilkins Ice Shelf 230 Glossary 232 Bibliography 235 Index 246 INTRODUCTION 7 Introduction 7 ater is at once simple and complex. Its study Wbegins with a single molecule. A water molecule consists of two hydrogen atoms and one oxygen atom, as noted by its chemical formula H2O. In water’s gaseous state, thermal energy—heat—enables single water mole- cules to float freely, mostly independently of one another. In water’s liquid state, hydrogen atoms constantly form and break bonds with other hydrogen atoms, as exhibited by water’s characteristic fluidity. In the solid phase, water’s molecular bonds are dictated by the oxygen atoms, which form crystalline shapes, or ice. On Earth, ice appears in many forms, from the ground-imbedded nature of permafrost to the towering majesty of mountainous glaciers. Each of these varied states is examined thoroughly in Glaciers, Sea Ice, and Ice Formation. Readers will virtually traverse pingos, rappel down cirques, and explore the frozen tundra of the Arctic and Antarctic as the complexities of this deceptively sim- ple entity are revealed. Unlike most materials, water’s solid state is less dense than its liquid state, a factor that explains why ice floats above liquid water. People witness natural ice formations seasonally on lakes, ponds, and other small bodies of water. As average daily temperatures fall, thermal energy is released from liquid water until the water’s surface temperature cools to the freezing point, and then below the freezing point—a process called supercooling. When this occurs, ice particles begin to form above the water’s surface. Though wind and currents typically interfere with the freezing process, ice can form on fast-flowing rivers. Ice crystals, called frazil, can appear as a thin layer of ice in a slow-moving river or as slush in faster currents. As ice forms, it slows down the velocity of the water. As long as 13 7 Glaciers, Sea Ice and Ice Formation 7 air temperatures remain below freezing 32° F (0°C) near the surfaces of lakes and rivers, ice will thicken from the bottom layers up. In other words, the water is at its cold- est when the freezing of its surface begins. As temperatures increase, however, ice on rivers and lakes decays due to the penetration of solar radiation. The salinity of the world’s oceans keeps them from freezing at the same temperature as bodies of freshwater. Salt ions disrupt the formation of ice crystals at the normal freezing temperature. However, in extreme polar areas, sea ice can form. There are three kinds of sea ice: landfast ice, which is attached to another surface or caught between icebergs; marine ice, which forms on the bottom of Antarctica’s ice shelves; and pack ice, which drifts with currents and wind. As with ice on lakes and rivers, sea ice experiences changes throughout the seasons. Sea ice serves several purposes, such as providing a habitat to ocean life. Arctic and Antarctic sea ice sup- ports bacteria, algae, and fungi that live off the nutritive brine and, in turn, become a food source for organisms such as krill. Sea ice also provides a measure of climate control. Snow that comes to rest on the ice insulates the ocean water from colder air above, retaining heat that influences weather and helps to sustain ocean life. Ice also forms on land as well as within bodies of water. Permafrost, which is moisture-laden ground that is frozen for two years or longer, covers about 20 percent of Earth’s surface.
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