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Mt. Rainier National Park
Mt. Rainier, at 14,411 feet, is the highest point in the Cascade Range, and around it are valleys, waterfalls, subalpine meadows, old-growth forest and more than 25 glaciers. The volcano is often shrouded in clouds that dump enormous amounts of rain and snow on the peak every year and hide it from the crowds that head to the park on weekends.
Mt. Rainier is considered one of the most dangerous volcanoes in the world, and it is on the Decade Volcano list. Because of its large amount of glacial ice, Mt. Rainier could potentially produce massive lahars that could threaten the entire Puyallup River valley, and poses a grave threat to sections of Seattle, a city of over 650,000 people with more than 3.7 million living in its metropolitan area.
Geology
Mount Rainier is a stratovolcano in the Cascade Volcanic Arc that consists of lava flows, debris flows, and pyroclastic ejecta and flows. Its early volcanic deposits are estimated at more than 840,000 years old and are part of the Lily Formation (about 2.9 million to 840,000 years ago). The early deposits formed a “proto-Rainier” or an ancestral cone prior to the present-day cone. The present cone is more than 500,000 years old.

The volcano is highly eroded, with glaciers on its slopes, and appears to be made mostly of andesite. Rainier likely once stood even higher than today at about 16,000 ft before a major debris avalanche and the resulting Osceola Mudflow approximately 5,000 years ago. In the past, Rainier has had large debris avalanches, and has also produced enormous lahars (volcanic mudflows) due to the large amount of glacial ice present. Its lahars have reached all the way to Puget Sound, a distance of more than 30 miles. Around 5,000 years ago, a large chunk of the volcano slid away and that debris avalanche helped to produce the massive Osceola Mudflow, which went all the way to the site of present-day Tacoma and south Seattle. This massive avalanche of rock and ice removed the top 1,600 ft of Rainier, bringing its height down to around 14,100 ft. About 530 to 550 years ago, the Electron Mudflow occurred, although this was not as large-scale as the Osceola Mudflow.
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