Clear Lake Volcanic Field

Summary

The town of Clearlake lies within the volcanic field, as does much of the 43,000-acre freshwater lake of its namesake. The Geysers steam field, which sits at the southwest margin of the volcanic region, is host to one of the world's most productive geothermal power plants, producing enough electricity for 850,000 homes. The heat driving the geothermal system emanates from a zone of partially molten rock (magma) deep below the greater Clear Lake volcanic system. The most prominent volcanic feature is 300,000 year-old Mount Konocti, rising about 975 m (3,200 ft) above the southwestern shore of the lake. The most recent activity in the Clear Lake Volcanic Field occurred between 8,500 and 13,500 years ago as explosive maar eruptions in and along the shores of the southeastern part of the lake. Although there have been no documented eruptions within the last few thousand years, sporadic volcanic-type earthquakes do occur, and the numerous springs and volcanic gas seeps in the field point to its potential for future eruptions. Monitoring in the Clear Lake region by the USGS, and a collaborative effort with Calpine Corporation in the Geysers Steam Field, provides real-time tracking of earthquake activity. In addition, the USGS periodically analyzes volcanic gases and hot springs in the region.