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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: 15 June 2021

Cataclysm!: The Hotspot Reaches Yellowstone

Cataclysm!: The Hotspot Reaches Yellowstone

Chapter:
3 Cataclysm!: The Hotspot Reaches Yellowstone
Source:
Title Pages
Author(s):

Robert B. Smith

Lee J. Siegel

Publisher:
Oxford University Press
DOI:10.1093/oso/9780195105964.003.0007

Epicenters from numerous earthquakes fall approximately along two parallel lines that stretch from southeast to northwest through Yellowstone National Park. During the past 630,000 years, lava flowed from eruptive vents located roughly along the same lines. The alignment of earthquakes and small volcanoes suggests that zones of weakness are deep beneath them within the Earth. Those zones may be the still-active roots of faults that once ran along the base of towering mountains. Such mountains would have made ancient Yellowstone resemble today’s Grand Teton National Park. Indeed, a few million years ago these mountains may have stretched northward through Yellowstone and hooked up with the Gallatin Range, which now extends from Montana south into Yellowstone’s northwest corner. So why is today’s Yellowstone Plateau relatively flat? What happened to the mountains that once may have rose thousands of feet skyward like the Tetons do today? The answer, quite simply, is that they were destroyed 2 million years ago during a caldera eruption, which is the largest, most catastrophic kind of volcanic outburst—an explosion so cataclysmic that it dwarfs any eruption in historic time. North America had continued its southwestward slide over the Yellowstone hotspot. After blasting and repaving the Snake River Plain, the hotspot was finally beneath the place for which it later was named. The power of its rising heat and hot rock began to shape Yellowstone into what it is today. The first eruptive blast at Yellowstone 2 million years ago left a gigantic hole in the ground—a hole larger than the state of Rhode Island. The huge crater, known as a caldera, measured about 5o miles long, 40 miles wide, and hundreds of yards deep. It extended from Island Park in Idaho to the central part of Yellowstone in Wyoming. During the volcanic cataclysm, hot ash and rock blew into the heavens over Yellowstone, then rained like hell from the sky. As heavier pumice and ash particles debris piled up on the ground, their heat welded the debris together to form a layer of solid rock called ash-flow tuff or welded tuff.

Keywords:   Ash-flow tuff, Calcite Springs, Domes, Flagg Ranch, Gallatin Range, Ice Age, Madison Plateau, Old Faithful, Pitchstone Plateau, Sierra Nevada

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