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America's Volcanic Past
The American West

"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994

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Map, The American West

Volcanic Highlights and Features:
[NOTE: This list is just a sample of various American West features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of the American West.]

  • The American West
  • America's Volcanic Past - The American West

The American West

The American West is one of the most unusual volcanic provinces on Earth. It is an extraordinary wide region of contemporaneous volcanism, stretching 1,800 kilometers (approximately 1,120 miles) from east of the Rocky Mountains to the west of the Cascades. It encompasses a very wide variety of volcanic landforms and diverse rock compositions, with the only consistency being small basalt fields that are scattered throughout the whole vast region. Intriguingly, except for the Cascadian segment, there is no currently active plate subduction to drive the volcanism, although there are hot spots, persistently "leaky" faults, and rifting.




Map, Location of the Pacific Mountain Region
Pacific Mountain System
Sierra Nevadas
Cascade Range Region

This region is one of the most geologically young and tectonically active in North America. The generally rugged, mountainous landscape of this province provides evidence of ongoing mountain-building. The Pacific Mountain System straddles the boundaries between several of Earth's moving plates -- the source of the monumental forces required to build the sweeping arc of mountains that extends from Alaska to the southern reaches of South America. This province includes the active and sometimes deadly volcanoes of the Cascade Range and the young, steep mountains of the Pacific Border and the Sierra Nevada.




Map, Location of the Columbia Plateau Region
Columbia Plateau Region

The Columbia Plateau province is enveloped by one of the worlds largest accumulations of lava. Over 500,000 square kilometers of the Earth's surface is covered by it. The topography here is dominated by geologically young lava flows that inundated the countryside with amazing speed, all within the last 17 million years. Over 170,000 cubic kilometers of basaltic lava, known as the Columbia River basalts, covers the western part of the province. These tremendous flows erupted between 17-6 million years ago. Most of the lava flooded out in the first 1.5 million years -- an extraordinarily short time for such an outpouring of molten rock. It is difficult to conceive of the enormity of these eruptions. Basaltic lava erupts at no less than about 1,100 degrees C. Basalt is a very fluid lava; it is likely that tongues of lava advanced at an average of 5 kilometers per hour - faster than most animals can run. Whatever topography was present prior to the Columbia River Basalt eruptions was buried and smoothed over by flow upon flow of lava. Over 300 high-volume individual lava flows have been identified, along with countless smaller flows. Numerous linear vents, some over 150 kilometers long, show where lava erupted near the eastern edge of the Columbia River Basalts, but older vents were probably buried by younger flows.



Map, Location of the Rocky Mountains Region
Rocky Mountain Region

The Rockies form a majestic mountain barrier that stretches from Canada through central New Mexico. Although formidable, a look at the topography reveals a discontinuous series of mountain ranges with distinct geological origins. The Rocky Mountains took shape during a period of intense plate tectonic activity that formed much of the rugged landscape of the western United States. Three major mountain-building episodes reshaped the west from about 170 to 40 million years ago (Jurassic to Cenozoic Periods). The last mountain building event, the Laramide orogeny, (about 70-40 million years ago) the last of the three episodes, is responsible for raising the Rocky Mountains.




Map, Location of Colorado Plateau
Colorado Plateau Region

The sculptured beauty and brilliant colors of the Colorado Plateau's sedimentary rock layers have captured the imaginations of countless geologists. This is a vast region of plateaus, mesas, and deep canyons whose walls expose rocks ranging in age from billions to just a few hundred years old.




Map, Location of the Basin and Range Region
Basin and Range Region

The Basin and Range province has a characteristic topography that is familiar to anyone who is lucky enough to venture across it. Steep climbs up elongate mountain ranges alternate with long treks across flat, dry deserts, over and over and over again! This basic topographic pattern extends from eastern California to central Utah, and from southern Idaho into the state of Sonora in Mexico. Within the Basin and Range Province, the Earth's crust (and upper mantle) has been stretched up to 100% of its original width. The entire region has been subjected to extension that thinned and cracked the crust as it was pulled apart, creating large faults. Along these roughly north-south-trending faults mountains were uplifted and valleys down-dropped, producing the distinctive alternating pattern of linear mountain ranges and valleys of the Basin and Range province.




Map, Location of Interior Plains
Interior Plains Region

The Interior Plains is a vast region that spreads across the stable core (craton) of North America. This area had formed when several small continents collided and welded together well over a billion years ago, during the Precambrian. Precambrian metamorphic and igneous rocks now form the basement of the Interior Plains and make up the stable nucleus of North America. With the exception of the Black Hills of South Dakota, the entire region has low relief, reflecting more than 500 million years of relative tectonic stability.




Excerpts from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., Contribution by Charles A. Wood; and USGS/NPS Geology in the Parks Website, 2001
   


America's Volcanic Past - The American West





Excerpts from:
1) Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., Contribution by Charles A. Wood

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10/30/01, Lyn Topinka