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California Volcano Observatory's mission
As a part of the U.S. Geological Survey's Volcano Hazards Program, the California Volcano Observatory aims to advance scientific understanding of volcanic processes and lessen the harmful impacts of volcanic activity in the volcanically active areas of California and Nevada.

Small Swarm in Long Valley 17 June 2013
June 18, 2013

In the late afternoon of 17 June 2013 a flurry of earthquakes started in the Long Valley Caldera east of the town of Mammoth Lakes, California (in an area known to geologists as the south moat). The swarm produced about 100 earthquakes over 5 hours before petering out; most were too small to be felt by humans (a magnitude 3.0 was the largest). The earthquakes originated at ~ 8-7 km depths where a small volume of partially molten rock is likely to reside.

Earthquake swarms are common in this part of the caldera, especially so in the 1980s and 1990s. A particularly intense swarm in the latter half of 1997 produced 12,000 events over 7 months, including eight earthquakes in the magnitude 4.0 range. Significant ground uplift accompanied the 1997-1998 swarm resulting in ~ 10 cm of caldera inflation. Yesterday's "mini swarm" pales in comparison, and does not indicate any immediate volcanic hazard within Long Valley Volcanic Center. The plots to the right (click to enlarge) show cumulative earthquake counts in the south moat for the past year as well as the number of earthquakes that occurred during the 17 June swarm. Modest, relatively steady inflation of the resurgent dome, located in the center of Long Valley Caldera, is a feature of the last couple of years, but CalVO deformation monitoring sensors show no changes related to the recent swarm.

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CalVO's Successful First Year of Operation
March 12, 2013

February 2013 marked the first year of successful volcano monitoring and preparing for possible volcanic eruption for the California Volcano Observatory (CalVO). At Long Valley Caldera, analysis of continuous GPS data over the first half of 2012 showed a modest inflationary pattern within the caldera; ground motion was directed upward and away from the caldera's center, with a maximum uplift rate between 2 and 3 cm/yr. In January of this year at Clear Lake Volcanic Field, a short-lived swarm of low-magnitude earthquakes was detected under the south flank of Mt Konocti.

CalVO also worked with other agencies this year to develop information to help people better understand and prepare for the potential for volcanic eruption. A statewide ash aviation plan was formulated in conjunction with the National Oceanic and Atmospheric Administration, Federal Aviation Administration, and the California Emergency Management Association. CalVO released the hazards assessment for Lassen Volcanic Center and helped to build an interactive exhibit at Lassen Volcanic National Park. The new exhibit, located at the Park's Loomis Museum, displays regional earthquake data and videos detailing the geologic processes that helped to form the volcanic landscape at Lassen.

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Volcano Hazards Discussed at Joint State and Federal Meeting
February 21, 2013

Many of California’s young volcanoes pose a threat to people and property. Volcanic eruptions occur in the State about as frequently as our largest San Andreas Fault Zone earthquakes: ten eruptions have occurred in California in the last 1000 years.

To better prepare for volcanic events in the State, the California Emergency Management Agency (Cal EMA), the USGS California Volcano Observatory, and the California Geological Survey are working together to produce the first ever Volcano Hazard Annex to the State Emergency Plan.

On February 12, 2013, a diverse group of state and federal stakeholders assembled at Cal EMA headquarters to discuss volcano hazards and identify State and Federal assets potentially at risk. Cal EMA’s new Volcano Annex will integrate hazard and socio-economic information in a format readily accessible to decision-makers at all levels of government.

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Lassen Hazards Assessment Published
October 01, 2012
A hazards assessment for Lassen Volcanic Center, California, is now available for download from the USGS Publications Warehouse. The Lassen region of the southernmost Cascade Range is an active volcanic area and will erupt in the future. At least 70 eruptions have occurred in the past 100,000 years, including 3 in the past 1,000 years, most recently in 1915. Although the annual probability of an eruption is small, the consequences of some types of eruptions could be severe. The hazards assessment and report presents a discussion of volcanic and other geologic hazards in the Lassen area and delineates hazards zones for different types of volcanic activity. Visit the Pubs Warehouse to download the report.

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High to Very High Threat Potential ¹
Clear Lake Volcanic Field
Lassen Volcanic Center
Long Valley Caldera
Medicine Lake
Mono-Inyo Chain
Mount Shasta
Salton Buttes
Moderate Threat Potential ¹
Coso Volcanic Field
Soda Lakes (NV)
Ubehebe Craters
Low to Very Low Threat Potential ¹
Brushy Butte
Eagle Lake Volcanic Field
Golden Trout Creek Volcanic Field
Lavic Lake Volcanic Field
Silver Lake Volcanic Field
Tumble Buttes
Twin Buttes

^{1. View the threat rankings of US Volcanoes.}