Erupting Volcano
Photo by Marc Szeglat

Since 1980, there have been 120 eruptions and 52 episodes of notable volcanic unrest at 44 U.S. volcanoes. 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.

The U.S. Geological Survey is updating its volcano threat assessments for the first time since 2005. The update names 18 very high threat, 39 high threat, 49 moderate threat, 34 low threat, and 21 very low threat volcanoes. The volcanoes are in Alaska, Arizona, California, Colorado, Hawaii, Idaho, Nevada, New Mexico, Oregon, Utah, Washington, Wyoming, American Samoa and the Commonwealth of the Northern Mariana Islands. The threat ranking is not an indication of which volcano will erupt next. Rather, it indicates how severe the impacts might be from future eruptions at any given volcano.

Very High Threat Volcanoes

Of the 18 “very high threat” volcanoes, five are in Alaska, four in Washington, four in Oregon and two in Hawaii. The danger list is topped by Hawaii’s Kilauea, which has been erupting this year. The others in the top five are Mount St. Helens and Mount Rainier in Washington, Alaska’s Redoubt Volcano and California’s Mount Shasta.

The agency says a dozen volcanoes have jumped in threat level since 2005. Twenty others dropped in threat level. There are 161 active U.S. volcanoes.

The USGS report says, volcanoes in the Cascade Range in Northern California, Oregon and Washington are particularly dangerous because “explosive and often snow- and ice-covered edifices can project hazards long distances to densely populated and highly developed areas.”

How Volcanoes are Classified

The USGS assesses active and potentially active volcanoes in the U.S., focusing on history, hazards and the exposure of people, property and infrastructure to harm during the next eruption. According to the USGS, “We use 24 factors to obtain a score and threat ranking for each volcano that is deemed potentially eruptable. The findings are published in the 2018 Update to the U.S. Geological Survey National Volcanic Threat Assessment.”

“The volcanic threat assessment helps prioritize U.S. volcanoes for research, hazard assessment, emergency planning, and volcano monitoring. It is a way to help focus attention and resources where they can be most effective, guiding the decision-making process on where to build or strengthen volcano monitoring networks and where more work is needed on emergency preparedness and response.”

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