ISBN 978-1-61530-106-5

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First Edition

Britannica Educational PublishingMichael I. Levy: Executive EditorJ. E. Luebering: Senior Manager Marilyn L. Barton: Senior Coordinator, Production ControlSteven Bosco: Director, Editorial TechnologiesLisa S. Braucher: Senior Producer and Data EditorYvette Charboneau: Senior Copy EditorKathy Nakamura: Manager, Media AcquisitionJohn P. Rafferty: Associate Editor, Earth Sciences

Rosen Educational ServicesAlexandra Hanson-Harding: EditorNelson S: Art DirectorCindy Reiman: Photography ManagerNicole Russo: DesignerMatthew Cauli: Cover DesignIntroduction by Therese Shea

Library of Congress Cataloging-in-Publication Data

Plate tectonics, volcanoes, and earthquakes / edited by John P. Rafferty. p. cm.(Dynamic Earth)In association with Britannica Educational Publishing, Rosen Educational Services.Includes index.ISBN 978-1-61530-187-4 ( eBook)1. Plate tectonics. 2. Volcanoes. 3. Earthquakes. 4. Geodynamics. I. Rafferty, John P.QE511.4.P585 2010551.8dc22

2009042303

Cover, pp. 12, 82, 302 www.istockphoto.com/Julien Grondin; p. 22 www.istockphoto.com/rni Torfason; pp. 23, 307 www.istockphoto.com; pp. 202, 305 www.istockphoto.com/Yali Shi

CONTENTS

Introduction 12

Chapter 1: Earths Dynamic Interior 23

The Process of Plate Tectonics 24Principles of Plate Tectonics 26 Continental and

Oceanic Crust 27 Plate Boundaries 28 Hot Spots 38 Plate Motion 40 The Development of Tectonic Theory 42 The Precursors of

Modern Thinking 43 Alfred Wegener and

the Concept of Continental Drift 44

The Renewed Interest in Continental Drift 48

Toward a Unifying Theory 54 Dissenting Opinions and

Unanswered Questions 58Plate Tectonics and the Geologic Past 62 The Wilson Cycle 62 The Supercontinent Cycle 65 Continental

Reconstructions 66

37

39

29

24

The Interaction of Tectonics with Other Systems 67 Earths Oceans 68 Life 69 Earths Climate 72Other Concepts Related to Plate Tectonics 74 Continental Drift 74 Diastrophism 78 Isostasy 78 Orogeny 81 Tectonics 81

Chapter 2: Volcanoes and Volcanism 82

Volcanic Eruptions 86 Lava, Gas, and Other

Hazards 86 Six Types of Eruptions 100 Two 20th-Century

Eruptions 104 The Four Worst Eruptions

in History 111 Volcano Forecasting and

Warning 113 Major Volcanoes of

the World 114 Signifi cant Volcanoes of

the World 128 Mount Agung 128 Askja 128 Mount Aso 129 Mount Cameroon 130 Cotopaxi 131 Mount Etna 132 Mount Fuji 134

Mount Hekla 135

89

90

107

130

Mount Hood 137 Iraz Volcano 138 Izalco Volcano 139 Kilauea 139 Klyuchevskaya

Volcano 142 Krakatoa 143 Lassen Peak 145 Mauna Loa 146 Mayon Volcano 148 Mount Unzen 148 Mount Nyamulagira 149 Mount Nyiragongo 150 Ol Doinyo Lengai 150 Paricutn 151 Pavlof Volcano 151 Mount Pele 152 Volcano Pico de

Orizaba 153 Mount Pinatubo 154 Popocatpetl 154 Mount Rainier 155 Mount Ruapehu 157 Mount Ruiz 159 Mount Saint Helens 159 Tajumulco Volcano 164 Mount Tambora 164 Teide Peak 165 Vesuvius 166Volcanic Landforms 169 The Major Types of

Volcanic Landforms 169 The Determinants of

Size and Shape 179 Hot Springs and Geysers 182 Cross Section of a

Geyser and Hot Spring 184

141

153

158

161

Volcanism and Tectonic Activity 186 Volcanoes Related to

Plate Boundaries 186 Volcanic Activity and the

Earths Tectonic Plates 188 Intraplate Volcanism 190Volcanoes and Geothermal Energy 191Related Concepts 193 Bomb 193 Fumarole 194 Kimberlite Eruption 194 Magma 196 Mofette 197 Volcanic Winter 197 Volcanism 199 Volcanology 201

Chapter 3: Earthquakes 202The Nature of Earthquakes 203 The Causes of

Earthquakes 204 The Eff ects of

Earthquakes 210 The Intensity and Magnitude

of Earthquakes 214 Modifi ed Mercalli Scale

of Earthquake Intensity 215 The Occurrence of

Earthquakes 220 Notable Earthquakes

in History 224Signifi cant Earthquakes 231 The Aleppo Earthquake

of 1138 232 The Shaanxi Province

Earthquake of 1556 232

188

203

212

The Lisbon Earthquake of 1755 233

The New Madrid Earthquakes of 181112 234

The Messina Earthquake and Tsunami 236

The Tokyo-Yokohama Earthquake of 1923 236

The San Francisco Earthquake of 1906 237

The Chile Earthquake of 1960 238

The Alaska Earthquake of 1964 238

The Ancash Earthquake of 1970 239

The Tangshan Earthquake of 1976 240

The Mexico City Earthquake of 1985 240

The San FranciscoOakland Earthquake of 1989 240

The Northridge Earthquake of 1994 241 The Ko-be Earthquake of 1995 243

The Izmit Earthquake of 1999 246

The Taiwan Earthquake of 1999 247

The Bhuj Earthquake of 2001 247

The Kashmir Earthquake 248 The Sichuan Earthquake

of 2008 248 The Haiti Earthquake

Of 2010 249

235

237

245

The Study of Earthquakes 250 Seismic Waves 251 The Observation of

Earthquakes 259 Earthquake Prediction 263 The Exploration of Earths Interior with Seismic

Waves 270 Extraterrestrial Seismic

Phenomena 278Related Concepts 279 Circum-Pacifi c Belt 279 Fault 280 Types of Faulting in

Tectonic Earthquakes 281 Richter Scale 283 Richter Scale of

Earthquake Magnitude 284 Seismic Belt 285 Seismic Survey 285 Seismograph 286 Noted Thinkers 294 Beno Gutenberg 294 Sir Harold Jeff reys 295 Augustus Edward

Hough Love 296 John Michell 297 John Milne 298 Harry Fielding Reid 299 Charles F. Richter 299 The Scope of Tectonic Forces 300

Glossary 302For Further Reading 305Index 307

268

275

281

295

INTRODUCTION

A volcano erupts on the island of Runion in the Indian Ocean. www.istockphoto.com/Julien Grondin

Humans live on unsteady ground. This fact was made abruptly apparent on January 12, 2010, when a magnitude 7.0 earthquake devastated the Caribbean island nation of Haiti. Because many buildings in this impoverished country were poorly constructed, they could not withstand the shaking and collapsed en masse, particularly in the capital city of Port-au-Prince, 15 miles from the quakes epicenter. Rescue workers des-perately combed through rubble, hunting for survivors. By early February, Haitis prime minister estimated that more than 200,000 people had been killed by the earthquakes effects. This type of earthquake, caused by two separate sections, or plates, of the Earths crust sliding against each other is known as a strike-slip earthquake. It is just one example of the restlessness of Earths surface.

This book will show how the movement of rock within the Earth is explained by the theory of plate tectonics, the idea that Earths outer layer is broken into moving pieces. It will show how Earth adds and subtracts land over time. In addition, it will explain how and why volca-noes erupt and earthquakes shake the ground we live on.

As early as 1620, scholars noticed that the outlines of continents could fi t together like puzzle pieces. In 1912, German scientist Alfred Wegener fi rst explained the concept of continental drift. He postulated that a single supercontinent, which he called Pangea, once existed, but broke apart into several pieces over geologic time.Wegener cited the existence of similar types of rocks and fossils found from separate continents as proof. He also used continental drift to explain the evidence of major climate and biological changes.

7 Introduction 7

13

7 Plate Tectonics, Volcanoes, and Earthquakes 7

14

By the late 1960s, scientists had pieced together the how of plate tectonics. Earths crustthe top layer of the lithosphereis broken into pieces called plates. The plates rest on and slide over a layer of plastic and molten rock. As the plates move, they shape the features of Earths surface above, including continents and oceans. Movement takes timea mere 5 to 10 cm (2 to 4 inches) per year in some places, less in others. Hundreds of millions of years have passed since Pangea began to separate into the land masses we know today.

The surface of each tectonic plate is made up of continental crust and oceanic crust. The continental crust is less dense and thus floats higher than oceanic crust. It is also about 40 km (25 miles) thick. While oceanic crust averages about 6.4 km (4 miles) thick. Tectonic plates interact at convergent, divergent, and transform boundaries.

When the boundary of oceanic crust meets, or con-verges with, continental crust, the more buoyant continental crust stays afloat while the oceanic crust is forced beneath ita process called subduction. The subducting crust melts under the pressure and heat of Earths mantle, and the process offers an explanation of why continental crust is generally older than oceanic crust. When two oceanic plates meet, the older plate subducts under the younger one. In contrast, when two continental crusts meet, neither gives w