How is mount rainier formed




















Although there are several 19th century reports of dark clouds at the summit, interpreted by observers as small eruptions, no ash or other related volcanic deposits have been found to confirm such recent activity. Scientific examination of sparse pumice formerly thought to have erupted between and , instead shows that this is 2, year old pumice.

Mount Rainier has been active for the last , years; so the 2,—year interval since the last known lava eruption is less than half a percent of the lifespan of the volcano.

Summit and crater at the top of Mount Rainier, Washington. Credit: Mullineaux, Don. Mount Rainier is chiefly made of andesite and some dacite lava flows and has erupted sizeable amounts of pumice throughout its history, though not as voluminously or as frequently as Mount St. Pyroclastic flows are a relatively minor component of Mount Rainier's eruptive products, and lava domes are almost unknown because itsandesitic magmas are more fluid than the stickier dacite magmas of Mount St.

Some portions of the upper volcano host sizeable areas of hydrothermally altered rock, but most of these rocks collapsed 5, years ago to form a massive lahar, known as the Osceola Mudflow.

As magma rose, rocks were heated and began to expand. Large lithospheric blocks dropped downward along north- south oriented faults creating linear depressions, or grabens fault- bounded basins. The faults opened pathways that enabled large volumes of magma to rise. The grabens filled and overflowed with overlapping shield and cinder cones to form a volcanic plateau called the Eastern, or High, Cascades. The present generation of volcanoes is believed to be no more than , , years old.

Mount St. Helens was formed only 40, years ago. Coincident with the growth of these recent volcanoes was the Pleistocene Ice Age, which began about 1.

Glaciers formed on each volcanic cone when it reached sufficient height. At the peak of glaciation, a continuous icecap buried the upper Cascades from Canada to northern California, broken only in the Columbia Gorge area where elevations approached sea level Kiver and Harris, Alpine glaciers on Mount Rainier flowed as far as 65 miles km from the mountain.

Most of the glacial sculpturing seen today occurred during the Wisconsin glacial stage, which reached its maximum only 15, 20, years ago.

Mount Rainier also has the distinction of having the greatest single- peak glacial system in the United States. Over 35 square miles 91 sq km of snow and ice cover this active volcano. Glaciers radiate from its summit so that its rocky, ice- mantled slopes above timberline contrast vividly with the green, verdant forests that include old growth trees.

The snowfields, alpine tundra with vivid alpine flowers, and dense forests provide the park visitor with a variety of visitor experiences. These names are more descriptive and perhaps capture the mountain's impact on the surrounding region better than the European moniker "Rainier", a name bestowed on the mountain by Captain Vancouver in in honor of his friend and superior officer, Rear Admiral Peter Rainier.

In terms of its potential impact on human populations, this "mountain of fire and ice" is the most dangerous volcano in the Cascade Range. In the shadow of Mount Rainier, live over 1. The glaciers on Mount Rainier provide a steady flow of water for hydroelectric power in the region, regardless of the season.

Forest Service. These parks, as well as other Cascade Mountain areas, contain world- class examples of volcanic and glacial features. Mount Rainier grew to an estimated 16, feet above sea level. About 5, years ago, the smoldering fires inside Mount Rainier erupted and the mountainside collapsed. Tons of rock, mud and debris rolled down the peak's northeast flank. A wall of mud feet high cascaded like a river of wet cement across square miles ending in the waters of Puget Sound.

This mud slide is called the Osceola Mudflow; the towns of Kent, Sumner, Auburn and Puyallup are built on top of the flow. Gone was the 16,foot summit, leaving a northeast-facing depression measuring nearly two miles in diameter. The Decade Volcano initiative is part of a United Nations program aimed at better utilizing science and emergency management to reduce the severity of natural disasters.

Mount Rainier was chosen to be studied because it is representative of one or more volcanic hazards: it is geologically active as evidenced by surface manifestation of heat geothermal activity , it has had recent volcanic events last eruption was about years ago , and it is likely to erupt again, based on past history; its location poses significant hazards to a heavily populated area; it is a well known volcano a number of research publications have been written on it ; it is politically and physically accessible for study; and its volcanic geology is well exposed.

In National Park Service staff participated with other agencies and individuals to develop a science plan through the National Academy of Sciences, for organizing the needed research to evaluate the hazards and risks associated with Mount Rainier and for developing communication efforts of the risks for appropriate planning activities.

The science plan was published in Mount Rainier Active Cascade Volcano and is available in the park library. Several studies related to geologic hazards are being conducted by the USGS , other federal and state agencies, and academic institutions.

History and Hazards of Mount Rainier - T. Show 10 40 per page. Explore This Park. Mount Rainier National Park Washington.



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