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Prior to 1980, Mount St. Helens had the shape of a conical, youthful volcano sometimes referred to as the Mount Fuji of America.


Summary

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 (1.2 x 2.2 mi) horseshoe-shaped crater now partially filled by a lava dome and a glacier. It is primarily an explosive dacite volcano with a complex magmatic system.

Mount St. Helens 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 New unpublished data on the timing for Mount St. Helens eruptive activity have been analyzed, which improves some of the eruption dates cited in published literature.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

Date published: September 11, 2019

“Science is Amazing”: GeoGirls Explore Mount St. Helens During Outdoor Science and Technology Program

Twenty-five middle school-age GeoGirls spent five days conducting hands-on research and interacting with female scientists, educators and older students, all while learning about active volcanoes, natural hazards and modern scientific monitoring technologies below the summit of Mount St. Helens.

Date published: October 15, 2018

GeoGirls Rock! USGS women encourage and support the next generation of scientists

Mount St. Helens volcano loomed in the distance as 25 middle-school “GeoGirls” signed in, received a name tag, dropped their overnight gear and gathered in a grassy open space to meet camp staff, women scientists and volunteers.

Date published: September 3, 2018

Scientists Discover New Clues to Mount St. Helens Unusual Location

The atypical location of Mount St. Helens may be due to geologic structures that control where deep magmas can rise through the crust, as suggested by new findings published today in Nature Geoscience.

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