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.
Three of the eighteen very high threat volcanoes are in California (Mount Shasta, Lassen and Long Valley) where explosive and snow- and ice-covered volcanoes can project ash or lahar (debris flow) hazards long distances to densely populated and highly developed areas.
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.
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The repetitive timing of this volcanic activity poses some interesting questions about hazards. The Lake Tahoe area is not currently considered to be volcanically active (it must have had an eruption in the last 10,000 years to meet that criteria). However, if magma were to return to the area, future eruptions and new lava dams would pose a flooding hazard both around the Lake Tahoe basin and beyond. Lava dams are known to fail rapidly, and a dam that raised the level of the lake and then collapsed could cause serious flooding downstream along the Truckee River. For now, however, there is no danger of an eruption, and such an event might be hundreds of thousands or even millions of years in the future - or might never occur at all.
Kortemeirer, W., Calvert, A., Moore, J.G., Schweickert, R., 2018, Pleistocene volcanism and shifting shorelines at Lake Tahoe, California: Geosphere, vol. 14, no. 2, 23 p. doi: 10.1130/GES01551.1.
The course is designed to give a primer on volcanic hazards and how the USGS monitors volcanoes and communicates in a crisis, but also devotes ample time to a tabletop eruption scenario where emergency managers are led through a fictional volcanic crisis and discuss how they would respond to escalating volcanic activity. The two-day course addresses the scientific, communication, managerial, and psychological aspects of volcanic crises, and allows insight into the goals of different groups in responding to volcanic hazards. CalVO scientists will conduct a similar training at Lassen Volcanic National Park in January 2018.
California is well-known for its frequent earth
Several new and updated field guides for the 2017 Scientific Assembly of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) in Portland, Oregon showcase California's volcanoes. Upcoming publications for Medicine Lake, Mount Shasta, Lassen Peak, Long Valley and Mammoth Mountain will provide easy to follow and informative field trips. The new collection of guidebooks can be found at the USGS Publications Warehouse and summarizes decades of advances in understanding volcanic and tectonic processes of western North America.