In its first update to the list of America’s most dangerous volcanoes since 2005, the United States Geological Survey (USGS) has listed the Washington state mountains of Mount St. Helens and Mount Rainier as posing a “very high threat” of eruption.
The USGS rating, detailed in the federal agency’s 2018 report, is based on the threat of eruption combined with the mountain’s proximity to densely-populated regions. Mount Rainier, the highest mountain in the Pacific Northwest, is about 50 miles from the Seattle-Tacoma region, and Mount St. Helens, which last erupted in 1980, is a similar distance from the Portland metro area.
Mount Rainier and Mount St. Helens ranked in the USGS’ top five most dangerous volcanoes, the others being Redoubt Volcano in Alaska and Mount Shasta in California. Topping the list was Hawaii’s Kilauea Volcano, which erupted earlier this year.
When Mount St. Helens erupted in May 1980, it killed 57 people, destroyed or damaged around 200 homes, and destroyed eight bridges, according to Oregon State University.
The eruption lasted nine hours, having been triggered by a 5.1 magnitude earthquake.
“A mushroom-shaped column of ash rose thousands of feet skyward and drifted downwind, turning day into night as dark, gray ash fell over eastern Washington and beyond. Wet, cement-like slurries of rock and mud scoured all sides of the volcano,” according to a U.S. Department of Agriculture Forest Service description of the events. “Mount St. Helens and the surrounding landscape were dramatically changed within moments.”
John Ewert of the Cascades Volcano Observatory in Vancouver, Washington, told KING 5 that while the Hawaii volcano of Kilauea produced destructive flowing lava, volcanic peaks in the Pacific Northeast “are both explosive and covered with a lot of snow and ice and can project those hazards pretty far downstream.”
Apart from Mount St. Helens and Mount Rainier, the USGS report says that another nine “very high threat” volcanoes are located in Washington, Oregon, or California. “Explosive and often snow- and ice-covered edifices can project hazards long distances to densely populated and highly developed areas.”
The USGS report noted that 1 in 10 active or potentially active volcanoes around the world is located on U.S. territory.
Mt. Hood, the highest peak in Oregon and the fourth-highest in the Cascade Range, is not an active volcano. However, researchers from Portland State University and the Oregon Department of Geology and Mineral Industries recently discovered seismic fault lines on the mountain that could trigger a 7.2 magnitude earthquake, KGW-TV reported.
Effects from the quake would, according to the researchers, be strong enough to knock a person off their feet.