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Windows into the EarthThe Geologic Story of Yellowstone and Grand Teton National Parks$
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Robert B. Smith and Lee J. Siegel

Print publication date: 2000

Print ISBN-13: 9780195105964

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195105964.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 21 June 2021

The Broken Earth: Why the Tetons Are Grand

The Broken Earth: Why the Tetons Are Grand

(p.89) 5 The Broken Earth: Why the Tetons Are Grand
Windows into the Earth

Robert B. Smith

Lee J. Siegel

Oxford University Press

On a summer morning when the breeze blows cool, it is easy to re the lakes and sagebrush-covered glacial plains of Wyoming’s Jackson Hole sit at nearly 7,000 feet elevation. Yet the altitude of this gorgeous valley is diminished by the view to the west: The precipitous east front of the Teton Range towers above the valley floor, with 13,770-foot Grand Teton and other rugged, snowclad peaks catching the first golden rays of daybreak. This is one of the most spectacular mountain vistas in America. Whether at chill dawn, in glistening light after a torrential afternoon thunderstorm, or during summer evenings when the sun descends behind the lagged Tetons, it is a view that brings solace and peace. Yet the serene splendor of Grand Teton National Park belies a hidden fury. It is not volcanism, which is concealed beneath the gentle pine-covered Yellowstone Plateau to the north. Instead, this defiant topography was born of seismic disaster as the Teton fault repeatedly and violently broke the earth, producing a few thousand magnitude-7 to -7.5 earthquakes during the past 13 million years. During each major jolt, Jackson Hole dropped downward and the Teton Range rose upward, increasing the vertical distance between the valley and the mountains by 3 to 6 feet and sometimes more. Now, after 13 million years of earthquakes, the tallest peaks tower almost 7,000 feet above the valley floor. Actual movement on the fault has been even greater. Jackson Hole dropped downward perhaps 16,000 feet during all those earthquakes. Rock eroded from the Teton Range and other mountains by streams and glaciers filled Jackson Hole with thousands of feet of sediment, disguising how much the valley sank. Combine the uplift of the mountains and the sinking of Jackson Hole, and the best estimate—although still plagued by uncertainty—is that movement on the Teton fault has totaled 23,000 feet during the past 13 million years. That is a tiny fraction of Earth’s 4.6-billion-year history. Consider the effects of repeated episodes of mountain-building during eons before the Teton fault was born: The oldest rocks high in the Teton Range are 2.8-billion-year-old gneisses and schists and 2.4-billion-year-old granites.

Keywords:   Angular unconformity, Bradley Lake, Colorado Plateau, Farallon plate, Grand Teton, Heise caldera, Jackson Lake, Leigh Lake, Middle Teton, Pacific Ocean

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