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<p>Rock Formations and Unusual Geologic Structures</p> <p>Rock Formations and Unusual Geologic StructuresExploring the EarTHs SurfacE Revised edition</p> <p>Jon ericksonForeword by Ernest H. Muller, Ph.D.</p> <p>ROCK FORMATIONS AND UNUSUAL GEOLOGIC STRUCTURES Exploring the Earths Surface, Revised Edition Copyright 2001, 1993 by Jon Erickson All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Facts On File, Inc. 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Erickson, Jon, 1948 Rock formations and unusual geologic structures : exploring the earths surface / by Jon EricksonRev. ed. p. cm. (The living earth) Includes bibliographical references and index. ISBN 0-8160-4328-0 (hardcover: alk. paper) 1. Geology. 2. Geomorphology. I.Title. QE33 .E75 2001 550dc21</p> <p>00-049038</p> <p>Facts On File books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions or sales promotions. Please contact our Special Sales Department at 212/967-8800 or 800/322-8755. You can find Facts On File on the World Wide Web at Text design by Cathy Rincon Cover design by Nora Wertz Illustrations by Dale Williams, Jeremy Eagle, and Dale Dyer, Facts On File Printed in the United States of America MP Hermitage 10 9 8 7 6 5 4 3 2 This book is printed on acid-free paper.</p> <p>CONTENTS</p> <p>Tables Acknowledgments Foreword Introduction 1 The Earths Crust: The Formation of Continents Precambrian Shields I Cratons I Terranes I Crystalline Rock Continental Crust I Oceanic Crust 2 EROSION AND SEDIMENTATION: THE BUILDING OF LANDFORMS Effects of Erosion I Drainage Patterns I Erosional Features Sedimentary Processes I Sedimentary Rocks I Sedimentary Structures</p> <p>ix xi xiii xv</p> <p>I</p> <p>1</p> <p>I</p> <p>25</p> <p>3 TYPE SECTIONS: DEFINING ROCK FORMATIONS Geologic Time I Age of the Earth I Faunal Succession I Relative Time I Rock Correlation I Dating Rocks I Geologic Formations I Geologic Mapping</p> <p>47</p> <p>4 FOLDING AND FAULTING: THE SHAPING OF THE LAND Tectonism I Mountain Building I Folded Strata I Fault Types Horsts and Grabens I Fault Belts I Earthquake Faults I Earthquakes 5 IGNEOUS ACTIVITY: VOLCANIC AND GRANITIC ROCKS Molten Magma I Volcanic Eruptions I Rift Volcanoes Calderas I Volcanic Rock I Granitic Intrusives I Kimberlite Pipes I Igneous Ore Bodies</p> <p>I</p> <p>72</p> <p>I</p> <p>96</p> <p>6 CANYONS, VALLEYS, AND BASINS: DEPRESSIONS IN THE EARTH Terrestrial Canyons I Submarine Canyons I Continental Rifts Oceanic Rifts I Deep-Sea Trenches I River Valleys I Desiccated Basins I The Great Basin 7 DESERTS AND SEACOASTS: WINDBLOWN AND BEACH SANDS Desert Features I Wind Erosion I Sand Dunes Sea Cliffs I Coastal Structures I Coral Reefs</p> <p>I</p> <p>122</p> <p>I</p> <p>Beach Sands</p> <p>I</p> <p>144</p> <p>8 GLACIAL TERRAIN: STRUCTURES FORMED BY GLACIERS The Ice Caps I Glacial Erosion I Glacial Deposits Glacial Valleys I Glacial Lakes I Surge Glaciers I Patterned Ground</p> <p>I</p> <p>167</p> <p>9 CAVES AND CAVERNS: DELVING BENEATH THE EARTHS SURFACE Cave Formation I Karst Terrain I Natural Bridges I Limestone Caves I Lava Caves I Ice Caves I Cave Deposits Cave Art 10 COLLAPSED STRUCTURES: CATASTROPHIC GROUND FAILURES Landslides I Liquefaction I Mass Wasting I Subsidence Catastrophic Collapse</p> <p>I</p> <p>191</p> <p>I</p> <p>212</p> <p>11 METEORITE IMPACT CRATERS: ASTEROID AND COMET COLLISIONS The Asteroid Belt I Asteroids and Comets I Cratering Rates I Meteorite Impacts I Crater Formation I Impact Structures I Meteorites I Strewn Fields 12 UNUSUAL FORMATIONS: CREATION OF UNIQUE ROCK FORMATIONS Rock Monuments I Pillars of Stone I Blowouts Potholes I Sod Pits I Fumaroles and Geysers I Crater Lakes I Lava Lakes Conclusion Glossary Bibliography Index</p> <p>238</p> <p>262 284 285 298 307</p> <p>tableS1 Common Igneous Rocks 2 Classification of the Earths Crust 3 Composition of the Earths Crust 4 Evolution of the Biosphere 5 The Geologic Time Scale 6 Frequently Used Radioisotopes for Geologic Dating 7 Summary of Earthquake Parameters 8 Comparison Between Types of Volcanism 9 The Ten Most Wanted List of Volcanoes 10 Classification of Volocanic Rocks 11 The Worlds Ocean Trenches 12 Major Deserts 13 The Major Ice Ages 14 Summary of Soil Types 15 Summary of Major Asteroids 16 Closest Calls with Earth 17 Locations of Major Meteorite Craters and Impact Structures 17 20 21 52 54 63 94 98 103 112 134 152 177 214 241 243 246IX</p> <p>ACKNOWLEDGMENTS</p> <p>he author thanks the National Aeronautics and Space Administration (NASA), the National Optical Astronomy Observatories (NOAO), the U.S.Army, the U.S.Army Corps of Engineers, the U.S. Department of Agriculture-Forest Service, the U.S. Department of Agriculture-Soil Conservation Service, the U.S. Department of Energy, the U.S. Geological Survey (USGS), and the U.S. Navy for providing photographs for this book. The author also thanks Frank K. Darmstadt, Senior Editor, and Cynthia Yazbek, Associate Editor, for their assistance in the preparation of this book.</p> <p>T</p> <p>XI</p> <p>foreword</p> <p>ROCK FORMATIONS AND UNUSUAL GEOLOGIC STRUCTURESToday people travel farther, faster, and more often than in past generations. This might well afford superb opportunity for making better acquaintance with wonders of the world around us. However, because we are in a hurry we often blindly miss out on the wealth of pleasure and information to be gained from rocks and landscapes. At time scales far greater than limits in everyday experience, our Earth is dynamic. Its components are constantly undergoing change. Weathering of rocks is recognizable between observations.Valleys are occasionally eroded overnight. Mountain ridges are elevated and worn down at rates so gradual as to escape ordinary perception. Through geologic time, ocean basins have changed in depth and configuration and slow drift has altered the shapes and relative positions of continents. Constant transformation in geologic time is unmistakable, and the evidence is at hand. Even inconspicuous rock fragments bear evidence of the past, available for compilation and correlation by geologists, but also to be noted and appreciated by alert and interested nonprofessionals. It is to the latter audience that Ericksons Rock Formations and Unusual Geologic Structures is directed as an introduction to geology, to alert the untutored but zealous observer to awareness of the origins, nature, and relevance of clues inherent in rocks and rock structures.This revised edition begins withXIII</p> <p>Rock Formations and Unusual Geologic Structures</p> <p>grand-scale generalizations on differentiation of Earths crust and dynamics of plate tectonism that account for continental masses and ocean basins. Ensuing chapters visit complex landscapes on truncated ancient igneous and metamorphic terranes. More gratifying for detailed analysis are sedimentary regions, products of weathering and erosion of older rocks followed by deposition in beds or strata. Even when complicated by folding and faulting, correlation of such beds in separate exposures can be facilitated by fossil content and reference to a previously described type section. Finally treated are unique features such as impact craters, rift lines, erosion remnants, caverns, and collapsed structures. Ernest H. Muller, Ph.D.</p> <p>XIV</p> <p>INTRODUCTION</p> <p>A</p> <p>mong the most impressive features our planet has to offer are its abounding rock formations and geologic structures.The Earths surface is covered by a thin veneer of sediments that provides an impressive terrain of ragged mountains and jagged canyons. The most fascinating geologic features were created by erosion. No other terrain can compare with mountain ranges, created by the forces of uplift and erosion. Some of the most magnificent scenery was carved from solid rock by running water and flowing ice.The removal of sediment by wind erosion scours the land, producing deflation basins and blowouts. The most spectacular examples of the handiwork of groundwater are caves. Over geologic time, water has dissolved great quantities of soluble rock, forming extensive mazes of tunnels in the Earths crust. Calderas form when the roof of a magma chamber collapses or when a powerful volcano decapitates itself, resulting in a broad depression.The dissolution of subsurface materials or the withdrawal of underground fluids causes the surface to sink, while other ground failures occur when subterranean sediments liquefy during earthquakes or violent volcanic eruptions. The surface of the Earth is sculpted by a number of forces, providing a cornucopia of unusual geological structures, ranging from narrow spires, mesas, ragged crags, and tall pillars carved out of stone; dikes and volcanic necks created by ancient volcanoes; arches and caves eroded out of solid rock; and meteorite and volcanic craters. The Earth possesses a variety of holes in the ground, including potholes, sinkholes, and numerous craters. Among theXV</p> <p>Rock Formations and Unusual Geologic Structures</p> <p>most unique depressions are kimberlite pipes, fumaroles and geysers, crater lakes, and lava lakes. These are just a few of the many wonders the Earths active geology has to offer. The text chronicles the formation of the Earths crustal rocks and their interactions with each other. It then examines the weathering, erosional, and sedimentary processes that create landforms. It discusses the type sections that define the Earths geologic features, including dating, correlating, and mapping geologic formations. It explains the forces that shape the Earths crust, including the folding and faulting of the Earths rocks. It examines the different types of igneous activity that shape the planet, including volcanoes and other igneous processes. After an examination of the basic building blocks of the Earths crust, the following chapters focus attention on specific types of rock formations and geologic structures. Some major depressions sculptured into the Earth include canyons, rift zones, trenches, valleys, and basins. The geologic features that define the arid and coastal regions, the landforms resulting from glacial erosion and deposition, and caves along with related structures are examined in great detail. Ground failures and collapsed structures and their impact on the Earths surface is discussed, as well as craters formed by meteorite impacts.The final chapter visits unique rock formations and geologic structures formed by unusual geologic activities. This revised and updated edition is a much expanded examination of rock formations and geologic structures. Science enthusiasts will particularly enjoy this fascinating subject and gain a better understanding of how the forces of nature operate on Earth. Students of geology and earth science will also find this a valuable reference book to further their studies. Readers will enjoy this clear and easily readable text that is well illustrated with evocative photographs, detailed illustrations, and helpful tables. A comprehensive glossary is provided to define difficult terms, and a bibliography lists references for further reading.The geologic processes that shape the surface of our planet are an example of the spectacular forces that create the living Earth.</p> <p>XVI</p> <p>1THE EARTHS CRUSTTHE FORMATION OF CONTINENTS</p> <p>his chapter examines the formation of crustal rocks, including the shields, cratons, and terranes that comprise the continents.The Earth, as with all the terrestrial planets, Mercury,Venus, and Mars, has a central core, surrounded by an intermediate layer, or mantle, and covered by a thin shell called the crust. The study of metallic meteorites, which once formed the cores of early planetoids that have disintegrated, suggests the Earths core is composed of iron and nickel. The age of the Earth, estimated at 4.6 billion years, is based on an agreement between the ages of meteorites thought to have formed at the same time as the planet. Furthermore, the ages of lunar rocks generally agree with the Earths oldest rocks, which formed about 4 billion years ago when the crust first segregated from the mantle. In the Earths early stages of formation, it was ceaselessly pounded by numerous giant meteorites. During this time, the planet was struck by as many as three Mars-sized bodies. One of these impactors might have been responsible for creating the Moon by launching great quantities of material into Earth orbit, where it coalesced into a satellite, the largest in the solar system relative to its mother planet.The giant impacts also might have initiated</p> <p>T</p> <p>1</p> <p>Rock FormationS and Unusual Geologic Structures</p> <p>the formation of continents by melting massive quantities of basalt.The continents grew quite rapidly, forming in a burst of creation starting as early as 4.2 billion years ago.The Earth is unique among planets because it is the only one known to have distinct continents, which are essentially thick slabs of granite riding on a sea of semimolten rock in the upper mantle. Underlying all other rocks on the Earths surface is a thick layer of basement complex, composed of ancient granitic and metamorphic rocks that have been in existence for nine-tenths of Earth history.These rocks form the nuclei of the continents and first appeared during a period of mantle segregation and outgassing, which created the crust along with the atmosphere and ocean. One remarkable feature about these rocks is that despite their great age they are similar to more recent rocks, signifying that geologic processes began quite early and had a long and productive life.</p> <p>PRECAMBRIAN SHIELDSAt the beginning of the Archean eon from about 4 billion to 2.5 billion years ago, the interior rocks that make up the Earths mantle gradually began to cool. This resulted in the creation of a permanent crust composed of a thin layer of basalt lava flows that erupted on the surface long before the ocean basins began to fill with water. Embedded in the thin basaltic crust were granitic blocks that assembled into microcontinents. These were lighter than the basalt, which enabled them to remain on the surface, drifting freely in the convection currents of the mantle as it pushed or pulled them along. Slices of granitic crust combined into stable bodies of basement rock, upon which all other rocks were deposited. The basement rocks formed the nuclei of the continents and are presently exposed in broad, low-lying domelike structures called shields.The shields are extensive uplifted areas essentially bare of recent sedimentary deposits. Many shields such as the Canadian Shield (Fig. 1), which covers most of eastern Canada and extends down into Wisconsin and Minnesota, are fully exposed in areas that were ground down by flowing ice sheets during the ice ages.The exposure of the Canadian shield from Manitoba...</p>


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