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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.

May 22 marks Lassen Peak's 97th eruption anniversary
May 22, 2012
On May 22, 1915 an explosive volcanic eruption occurred at Lassen Peak, California. It was the most powerful single explosion from the series of eruptions that lasted from 1914-1917. It generated a high eruption column, pyroclastic flows, and lahars. Lassen Volcanic Center is still active today and the USGS California Volcano Observatory monitors its activity daily. For more information about this eruption, please read our fact sheet that details the events.

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Hello CalVO
January 10, 2012

Welcome to the new USGS California Volcano Observatory website! The USGS Volcano Science Center recently restructured observatory operations to optimize volcano monitoring, eruption forecasting, and hazard mitigation efforts throughout California. The new USGS California Volcano Observatory (CalVO), headquartered in Menlo Park CA, replaces the former Long Valley Observatory (LVO), which was established in 1982 to monitor the restless Long Valley Caldera and Mono-Inyo Craters region of Eastern California.

Scientists at the five USGS volcano observatories research, monitor, and assess hazards at United States volcanoes and provide activity notifications and eruption warnings in the event of volcanic crises. The volcano monitoring responsibility of CalVO includes all potentially active volcanoes in California and Nevada. The Cascade Volcano Observatory (CVO), CalVO’s sister observatory in Vancouver, WA, oversees efforts at all potentially active volcanoes in Oregon, Washington, and Idaho. CalVO and CVO share scientific expertise, administrative staff, and equipment, ensuring a strategic and cost efficient program of volcanic hazard mitigation.

Note: The Yellowstone Volcano Observatory (YVO in Menlo Park, CA) monitors volcanoes in Montana, Wyoming, Colorado, Utah, New Mexico, and Arizona. The Alaska Volcano Observatory (AVO in Anchorage, AK) oversees Alaskan volcanoes and those within the Commonwealth of the Northern Mariana Islands. The oldest USGS volcano observatory, the Hawaiian Volcano Observatory (HVO in Hawaii National Park, HI), is responsible for the state of Hawaii and is celebrating its 100^th anniversary this year.

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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.}