Major Volcanoes of the World

Mount Rainier

Mount Rainier is a stratovolcano in Pierce County, Washington, located 54 miles (87 km) southeast of Seattle, Washington, in the United States. It is part of the Cascade Volcanic Arc and is the highest peak in the Cascade Range at 14,410 feet (4,392 m). The mountain and the surrounding area are protected within Mount Rainier National Park. With 26 major glaciers, Mount Rainier is the most heavily glaciated peak in the lower 48 states with 35 square miles (91 km²) of permanent snowfields and glaciers. The summit is topped by two volcanic craters, each over 1,000 feet (300 m) in diameter with the larger east crater overlapping the west crater. Geothermal heat from the volcano keeps areas of both crater rims free of snow and ice, and has formed an extensive network of glacier caves within the ice-filled craters. A small crater lake, the highest in North America, occupies the lowest portion of the west crater below more than 160 ft (50 m) of ice and is accessible only via the caves.
Mount Rainier was originally known as Talol, or Tahoma. It has a topographic prominence of 13,210 feet (4,026 m), greater than that of K2. It is a prominent feature of the southern landscape in most of the Seattle metropolitan area. On clear days, it can also be seen from as far away as Portland, Oregon, and Victoria, British Columbia. Because of its scenic dominance, Seattle-Tacoma-area residents often refer to it simply as "the Mountain."
The Carbon, Puyallup, Nisqually, and Cowlitz Rivers begin at eponymous glaciers of Mount Rainier. The sources of the White River are Winthrop, Emmons, and Fryingpan Glaciers. The White and Carbon join the Puyallup River, which discharges into Commencement Bay at Tacoma; the Nisqually empties into Puget Sound east of Lacey; and the Cowlitz joins the Columbia River between Kelso and Longview.

Geological history
Mount Rainier's earliest lavas are over 840,000 years old and are part of the Lily Formation (2.9 million to 840,000 years ago). The early lavas formed a "proto-Rainier" or an ancestral cone prior to the present-day cone. The present cone is over 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 feet (4,900 m) before a major debris avalanche and the resulting Osceola Mudflow 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 the Puget Sound. 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 took out the top 1,600 feet (500 m) of Rainier, bringing its height down to around 14,100 feet (4,300 m). About 530 to 550 years ago, the Electron Mudflow occurred, although this was not as large-scale as the Osceola Mudflow.
After the major collapse 5,000 years ago, subsequent eruptions of lava and tephra built up the modern summit cone until about as recently as 1,000 years ago. As many as 11 Holocene tephra layers have been found.
The most recent recorded volcanic eruption was between 1820 and 1854, but many eyewitnesses reported eruptive activity in 1858, 1870, 1879, 1882 and 1894 as well.[4] As of 2007, there is no imminent risk of eruption, but geologists expect that the volcano will erupt again.
Lahars from Rainier pose the most risk to life and property, as many communities lie atop older lahar deposits. Not only is there much ice atop the volcano, the volcano is also slowly being weakened by hydrothermal activity. According to Geoff Clayton, a geologist with RH2, a repeat of the Osceola mudflow would destroy Enumclaw, Kent, Auburn, and most or all of Renton. Such a mudflow might also reach down the Duwamish estuary and destroy parts of downtown Seattle, and cause tsunamis in Puget Sound and Lake Washington. Rainier is also capable of producing pyroclastic flows as well as lava.
Descending from the summit ice cap, Tahoma Glacier is flanked by Puyallup and South Tahoma Glaciers