Mount St. Helens and Mount Rainier, both in Washington state, have both been classified by a federal agency as a “very high threat” for an eruption.
The updated classification was announced in a new volcanic threat assessment report (pdf) by the United States Geological Survey (USGS), the first update to the list of the nation’s most dangerous volcanoes since 2005.
The rating system combines the threat of an eruption with the proximity to high populations and potential impact.
Both Mount St. Helens and Mount Rainier are in the top five, along with Redoubt Volcano in Alaska and Mount Shasta in California; at the top is the Kilauea Volcano in Hawaii, which erupted earlier this year. The United States has more than 10 percent of the world’s known active and potentially active volcanoes within its territory, the researchers noted.
‘Explosive’
While the lava flowing from Kilauea caused serious damage, an expert noted that the volcanoes in the Pacific Northwest explode.
“In the Pacific Northwest, we don’t have much development on our flanks. But our volcanoes are both explosive and covered with a lot of snow and ice and can project those hazards pretty far downstream,” John Ewert of the Cascades Volcano Observatory in Vancouver, Washington, told KING 5.
The report notes that eleven of the 18 “very high threat” volcanoes are located in Washington, Oregon, or California, “where explosive and often snow- and ice-covered edifices can project hazards long distances to densely populated and highly developed areas.”
Besides killing people, volcanoes inflict severe damage in the surrounding environment, killing trees, animals, and plants; choking major riverways; and destroying roads, bridges, and other infrastructure. The danger has gotten higher in recent years as populations near a number of volcanoes have risen.
1980 Eruption
Mount St. Helens erupted on May 18, 1980, shaken 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. Searing flows of pumice poured from the crater. The eruption lasted 9 hours, but Mount St. Helens and the surrounding landscape were dramatically changed within moments,” said the U.S. Department of Agriculture’s Forest Service, describing the scene that day.
Fifty-seven people died that day, killed by asphyxiation, thermal injuries, and trauma, among other causes, according to Oregon State University.
Some 200 homes were destroyed or damaged and eight bridges were destroyed.
