Mount Rainier ( ), also known as Tahoma ( ), is a large, active stratovolcano in the Cascade Range of the Pacific Northwest in the United States. The mountain is located in Mount Rainier National Park about south-southeast of Seattle. At 14,406ft () it is the highest mountain in the U.S. state of Washington, the most topographically prominent mountain in the contiguous United States, and the tallest in the Cascade Volcanic Arc.
Due to its high probability of an eruption in the near future and proximity to a major urban area, Mount Rainier is considered one of the most dangerous volcanoes in the world, and it is on the Decade Volcano list. The large amount of glacial ice means that Mount Rainier could produce massive lahars that could threaten the entire Puyallup River valley and other river valleys draining Mount Rainier, including the Carbon, White, Nisqually, and Cowlitz (above Riffe Lake). According to the United States Geological Survey's 2008 report, "about 80,000 people and their homes are at risk in Mount Rainier's lahar-hazard zones."
Between 1950 and 2022, 471,792 people attempted to climb Mount Rainier according to NPS statistics. Approximately 84 people died in mountaineering accidents on Mount Rainier from 1947 to 2018.
Name
The many Indigenous peoples who have lived near Mount Rainier for millennia have many names for the mountain in their various languages. A linguistic analysis published in 2025 identified 20 indigenous names for the mountain.
Lushootseed speakers have several names for Mount Rainier, including and . means "sky wiper" or "one who touches the sky" in English. The word means "snow-covered mountain". has been anglicized in many ways, including "Tacoma" and "Tacobet".
Cowlitz speakers call the mountain or . Sahaptin speakers call the mountain , which is borrowed from Cowlitz.
Another anglicized name is Pooskaus.
George Vancouver named Mount Rainier in honor of his friend, Rear Admiral Peter Rainier. The map of the Lewis and Clark expedition of 1804–1806 refers to it as "Mt. Regniere". Although Rainier had been considered the official name of the mountain, Theodore Winthrop referred to the mountain as "Tacoma" in his posthumously published 1862 travel book The Canoe and the Saddle. For a time, both names were used interchangeably, although residents of the nearby city of Tacoma preferred Mount Tacoma.
In 1890, the United States Board on Geographic Names declared that the mountain would be known as Rainier. Following this in 1897, the Pacific Forest Reserve became the Mount Rainier Forest Reserve, and the national park was established three years later. Despite this, there was still a movement to change the mountain's name to Tacoma, and Congress was considering a resolution to change the name as late as 1924.
Geographical setting
Mount Rainier is the tallest mountain in Washington and the Cascade Range. This peak is located southeast of Tacoma, approximately south-southeast of Seattle. Mount Rainier has a topographic prominence of . On clear days it dominates the southeastern horizon in most of the Seattle-Tacoma metropolitan area to such an extent that locals sometimes refer to it simply as "the Mountain". On days of exceptional clarity, it can also be seen from as far away as Corvallis, Oregon (at Marys Peak), and the North Shore Mountains in British Columbia.
With 26 major glaciers and of permanent snowfields and glaciers, Mount Rainier is the most heavily glaciated peak in the lower 48 states. The summit is topped by two volcanic craters, each more than 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 the world's largest volcanic glacier cave network has formed within the ice-filled craters, with nearly of passages. A small crater lake about in size and deep, the highest in North America with a surface elevation of , occupies the lowest portion of the west crater below more than of ice and is accessible only via the caves.
The Carbon, Cowlitz, Nisqually, Puyallup and North Mowich Rivers begin at eponymous glaciers of Mount Rainier. The sources of the White River are Winthrop, Emmons, and Fryingpan Glaciers. The White, Carbon, and Mowich join the Puyallup River, which discharges into Commencement Bay at Tacoma. The Nisqually empties into Puget Sound east of Lacey. The Cowlitz joins the Columbia River between Kelso and Longview.
Subsidiary peaks
The broad top of Mount Rainier contains three named summits. The highest of these named summits is known as the Columbia Crest. The second-highest summit is Point Success, , at the southern edge of the summit plateau, atop the ridge known as Success Cleaver. It has a topographic prominence of about , so it is not considered a separate peak. The lowest of the three summits is Liberty Cap, , at the northwestern edge, which overlooks Liberty Ridge, the Sunset Amphitheater, and the dramatic Willis Wall.Named after Bailey Willis, USGS geological engineer, who played a key role in getting Mount Rainier designated as a national park.
High on the eastern flank of Mount Rainier is a peak known as Little Tahoma Peak, , an eroded remnant of the earlier, much higher, Mount Rainier. It has a prominence of , and it is rarely climbed in direct conjunction with Columbia Crest, so it is usually considered a separate peak. If considered separately from Mount Rainier, Little Tahoma Peak would be the third-highest mountain peak in Washington.
Height of the mountain Mount Rainier was one of five historical icecap summits in the lower 48 states, meaning that its elevation has changed as a result of glacial melting due to climate change. The National Park Service and United States Geological Survey cite Mount Rainier's summit as the Columbia Crest icecap at ; this value was determined in 1956, referenced to the National Geodetic Vertical Datum of 1929 (NGVD29). In 1999, the mountain summit was surveyed at , also in the NGVD29.
In the 2020s, Eric Gilbertson and other surveyors found that the Columbia Crest had melted down so that it was no longer the highest point on the mountain after around 2014. According to Gilbertson's research, the current summit of the mountain is a point of bare rock on the southwest crater rim at +/- . This figure also uses the NGVD29 datum. Mount Rainier National Park geologists expressed concerns over the methods used in the study and requested the data for evaluation, though they recorded similar glacial thinning. An official measurement taken in 2010 saw little to no change from the official value.
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 before 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 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 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 . 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 traveled as far as present-day Tacoma and south Seattle. This massive avalanche of rock and ice removed the top of Rainier, bringing its height down to around . 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 approximately 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.
Soils on Mount Rainier are mostly gravelly, ashy sandy loams developed from colluvium or glacial till mixed with volcanic tephra. Under forest cover, their profiles usually have the banded appearance of a classic podzol, but the E horizon is darker than usual. Under meadows, a thick dark A horizon usually forms the topsoil.
Modern activity and threat
The most recent recorded volcanic activity was between 1820 and 1854, but many eyewitnesses reported eruptive activity in 1858, 1870, 1879, 1882, and 1894 as well. Additionally, the Smithsonian Institution's volcanism project records the last volcanic eruption as 1450 CE.
Seismic monitors have been placed in Mount Rainier National Park and on the mountain itself to monitor activity. Because of the massive amounts of ash blasting out of the volcano into the atmosphere, an eruption could be deadly for all living in areas within the immediate vicinity. Effects from an eruption could be noticed from Vancouver, British Columbia to as far as San Francisco, California.
Mount Rainier is located in an area that itself is part of the eastern rim of the Pacific Ring of Fire. This includes mountains and calderas like Mount Shasta and Lassen Peak in California, Crater Lake, Three Sisters, and Mount Hood in Oregon, Mount St. Helens, Mount Adams, Glacier Peak, and Mount Baker in Washington, and Mount Cayley, Mount Garibaldi, Silverthrone Caldera, and Mount Meager in British Columbia. Many of the above are dormant, but could return to activity, and scientists on both sides of the border gather research of the past eruptions of each to predict how mountains in this arc will behave and what they are capable of in the future, including Mount Rainier. Of these, two have erupted since the beginning of the twentieth century: Lassen in 1915 and St. Helens in 1980 and 2004. However, past eruptions in this volcanic arc have multiple examples of sub-plinian eruptions or higher: Crater Lake's last eruption as Mount Mazama was large enough to cause its cone to collapse, and Mount Rainier's closest neighbor, Mount St. Helens, produced the largest recorded eruption in the continental United States when it erupted in 1980. Statistics place the likelihood of a major eruption in the Cascade Range at 2–3 per century.
Mount Rainier is listed as a Decade Volcano, or one of 16 volcanoes on Earth with the greatest likelihood of causing loss of life and property if eruptive activity resumes. If Mount Rainier were to erupt as powerfully as Mount St. Helens did in its May 18, 1980 eruption, the effect would be cumulatively greater, because of the far more massive amounts of glacial ice locked on the volcano compared to Mount St. Helens, the vastly more heavily populated areas surrounding Rainier, and the fact that Mount Rainier is almost twice the size of St. Helens. Lahars from Rainier pose the most risk to life and property, as many communities lie atop older lahar deposits. According to the United States Geological Survey (USGS), about 150,000 people live on old lahar deposits of Rainier. Not only is there much ice atop the volcano, but the volcano is also slowly being weakened by hydrothermal activity. According to Geoff Clayton, a geologist with a Washington State Geology firm, RH2 Engineering, a repeat of the 5,000-year-old Osceola Mudflow would destroy Enumclaw, Orting, Kent, Auburn, Puyallup, Sumner and 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 and expelling lava. A 2012 Washington State Department of Natural Resources estimate showed that a significant lahar could cause up to $40 billion in damage downriver.