Volcanic Threat Assessment help prioritize risk reduction efforts at U.S. volcanoes.

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 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. The assessment uses 24 factors to obtain a score and threat ranking. The findings are in the newly published 2018 Update to the U.S. Geological Survey National Volcanic Threat Assessment.

Eleven of the eighteen very high threat volcanoes are in Washington, Oregon, or California, where explosive and often snow- and ice-covered volcanoes can project ash or lahar (debris flow) hazards long distances to densely populated and highly developed areas. These include Mount St. Helens, Mount Rainier, Mount Hood, Three Sisters, Newberry, Mount Baker, Glacier Peak and Crater Lake (in Washington and Oregon), and Mount Shasta, Lassen and Long Valley (in California). The threat ranking is not a list of which volcano will erupt next. Rather, it indicates how severe the impacts might be from future eruptions at any given volcano.

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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