GEOLOGY / NATURE G e o l o g y o GGGeeeooolllooogggyyy ooofff f S o SSSooouuuttthhheeeaaasssttt AAAlllaaassskkkaaa u t h The most powerful forces on earth have e a shaped the landscape of Southeast Alaska. s Scientists and visitors from around the world t A trek north to experience wild rivers, powerful l glaciers, and breathtaking mountain peaks. a s Now, for the fi rst time, a handy guide to the k a region is available. Complete with color illus- R trations revealing millions of years of geologi- O C cal history and in-depth descriptions of Sitka, K Juneau, and Glacier Bay, Geology of Southeast A N Alaska is essential reading for anyone fasci- D I nated by rock and ice in motion. C E I N Harold H. Stowell is professor of geology M at the University of Alabama. He began his O T career in 1979 as an exploration geologist IO N and received his doctorate from Princeton University in 1987. Dr. Stowell‘s fi eldwork has S T taken him to Alaska and Canada, as well as to O W New Zealand, Antarctica, and Svalbard. He is a E L fellow of the Geological Society of America. L U N IV E R S IT Y O F AL HHaarroolldd HH.. SSttoowweellll A S K A P R E S S This page intentionally left blank Geology of Southeast Alaska Rock and Ice in Motion This page intentionally left blank Geology of Southeast Alaska Rock and Ice in Motion Harold H. Stowell University of Alaska Press Fairbanks © 2006 University of Alaska Press P.O. Box 756240 Fairbanks, AK 99775-6240 Printed in China This publication was printed on paper that meets the minimum requirements for ANSI/NISO x39.48-1992 (Permanence of Paper). ISBN 13: 978-1-889963-81-5 ISBN 10: 1-889963-81-X Library of Congress Cataloging-in-Publication Data Stowell, Harold Hilton. Geology of southeast Alaska : rock and ice in motion / Harold H. Stowell. p. cm. Includes bibliographical references. ISBN-13: 978-1-889963-81-5 (pbk. : alk. paper) ISBN-10: 1-889963-81-X (pbk. : alk. paper) 1. Geology—Alaska, Southeast. 2. Glaciers—Alaska, Southeast. 3. Plate tectonics—Alaska, Southeast. 4. Climate—Alaska, Southeast. I. Title. QE84.S68S76 2006 557.982—dc22 2005027066 All illustrations by Harold H. Stowell unless otherwise noted. Cover and interior text design by Dixon J. Jones, UAF Rasmuson Library Graphics Book production by Sue Mitchell Cover image: the Fairweather Range; the terminus of Brady Glacier is visible at the base of the mountains. Back cover images: (top) sea arch on Kuiu Island; (center) infrared aerial photo- graph of Margerie, Ferris, and Grand Pacifi c glaciers; (bottom) glacial grooves cut into the Coast Plutonic Complex sill along the south shore of Tracy Arm. Sun and glacial silt produce the intense blue-green water color. To those who contribute to understanding the geology and to preserving the unique environment of Southeast Alaska and especially to Kim Ouderkirk, who provided moral and physical support throughout the research and writing of this book. This page intentionally left blank Table of Contents Acknowledgments ix Introduction xi 1 Geography of Southeast Alaska 1 2 Glaciers, Ice Ages, and Global Change 7 3 Plate Tectonics: A Geologic Paradigm 23 4 Rock Types: Classifi cation of Earth Materials 33 5 Faults, Earthquakes, and Mountain Building 39 6 The Alexander Archipelago 45 7 The Coast Mountains: Exhumed Lower Crust 53 8 Regional Geology 59 Notes 110 Glossary of Geological Terms 113 Bibliography 127 Index 134 This page intentionally left blank