Mount St. Helens
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Mount St. Helens
Prior to 1980, Mt. St. Helens had the shape of a conical volcano sometimes referred to as the Mount Fuji of America. During the 1980 eruption the upper 400 m (1,300 ft) of the summit was removed by a huge debris avalanche, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome and a glacier. It is primarily an explosive dacite volcano.
Quick Facts
Location: Washington, Skamania County
Latitude: 46.2° N
Longitude: 122.18° W
Elevation: 2,539 (m) 8,330 (f)
Volcano type: Stratovolcano
Composition: Basalt to Rhyodacite
Most recent eruption: 1980, 2004-2008
Nearby towns: Castle Rock, WA; Olympia, WA; Vancouver, WA; Yakima, WA; Portland, OR
Threat Potential: Very High*
*based on the National Volcano Early Warning System
Summary
Mount St. Helens is primarily an explosive dacite volcano with a complex magmatic system. The volcano was formed during four eruptive stages beginning about 275,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to about 12,800 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but a few lava flows extended beyond the base of the volcano. The bulk of the modern edifice (above the 1980 crater floor) was constructed during the last 3,000 years, when the volcano erupted a wide variety of products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers. New unpublished data on the timing for Mount St. Helens eruptive activity have been analyzed, which improves some of the eruption dates cited in published literature. This website contains the most up to date information.
Since its 1980 eruption, the summit elevation has decreased. A survey in 1982 gave a measurement of 2549.7 m (8365 ft). However, a lidar survey done in 2009 found the maximum elevation to be 2539 m (8330 ft). The difference in elevation is likely due to erosion and loss of rimrock by crater-wall collapses.
News
CVO dismantles Mount St. Helens’ VALT seismic station after 18 years in service.
Mount St. Helens seismicity elevated but within the range of background levels (February to June 2024)
Uptick in earthquake activity at Mount St. Helens remains within background levels (July 15 - December 2023)
Publications
2018 update to the U.S. Geological Survey national volcanic threat assessment
When erupting, all volcanoes pose a degree of risk to people and infrastructure, however, the risks are not equivalent from one volcano to another because of differences in eruptive style and geographic location. Assessing the relative threats posed by U.S. volcanoes identifies which volcanoes warrant the greatest risk-mitigation efforts by the U.S. Geological Survey and its partners. This update
