The California Volcano Observatory (CalVO) monitors volcanoes in the states of California and Nevada for signs of unrest (activity). Detectable movement of molten rock or volcanic gas beneath a volcano will precede a large eruption. Depending on the volcanic system, these precursors give scientists and emergency response teams sufficient time to ensure the safety of populations living around active volcanoes. Continuous monitoring is necessary to determine the baseline, or background signal, of activity at a volcano and helps volcanologists to know what is normal. Any shift toward abnormal may be a sign of volcanic unrest.
There are several modern instrumental methods of volcano monitoring being employed by the USGS. These technologies are part of the toolbox that volcanologists use to interpret the future behavior of a volcano. The three key types of monitoring techniques measure earthquakes (seismicity), the movement of the ground surface (deformation), and the amount and chemistry of gas released from a volcano.
An added challenge for CalVO is that monitoring equipment is co-located with active geothermal systems and dangerous faults. Therefore, monitoring plans must take into account an added layer of complexity and data must be closely analyzed to parse out what is volcanic vs. tectonic vs. geothermal in nature.
To view the available data and to learn more about monitoring at specific California and Nevada volcanoes, please use the links below. Note that some volcanoes are more heavily monitored than others due to their threat potential, size, and location to nearby cities and towns.