The U.S. Geological Survey California Volcano Observatory (USGS CalVO) was formed in 2012 and is headquartered in Menlo Park CA. It replaced 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. CalVO now monitors these and other potentially hazardous volcanoes in California and Nevada to help communities and government authorities understand, prepare for, and respond to, volcanic activity. The observatory deploys sensors like the Global Positioning System (GPS) receiver, seismometer, and multi-gas spectrometer o detect ground deformation, seismicity, and gas emissions that occur in the weeks to months prior to an eruption.
Volcanic eruptions occur in the State about as frequently as M6 or larger earthquakes on the San Andreas Fault. At least ten eruptions have taken place in the past 1,000 years—the most recent is the Lassen Peak eruption of 1914 to 1917 in Northern California—and future volcanic eruptions are inevitable.
Volcanic eruptions will occur in California in the future. Sixteen young volcanoes designated as Low Threat to Very High Threat are dispersed throughout the State. Partially molten rock (magma) resides beneath at least seven of these—Medicine Lake Volcano, Mount Shasta, Lassen Volcanic Center, Clear Lake Volcanic Field, the Long Valley Volcanic Region, Coso Volcanic Field, and Salton Buttes— producing volcanic earthquakes (seismicity), toxic gas emissions, hot springs, and (or) ground movement (deformation).
The USGS California Volcano Observatory has the responsibility to issue timely notifications of volcanic hazards for both escalating (increasing risk) and deescalating (decreasing risk) conditions. Notifications (https://volcanoes.usgs.gov/vhp/notifications.html) take the form of Volcano Alert Notices (VANs) and Volcano Observatory Notices for Aviation (VONAs), both of which use a four-tiered system to describe threat levels. Alerts and other information are conveyed to government officials, land managers, and emergency responders through telephone call downs, official emails and faxes, and face-to-face briefings. The public can get alerts and other information through the CalVO website, public meetings, media interviews, and an email-based Volcano Notification Service (VNS) that automatically delivers customized notifications to subscribers.