The Volcano Adventure Guide: Excellent information and background for anyone wishing to visit active volcanoes safely and enjoyably. The book presents guidelines to visiting 42 different volcanoes around the world.
Clear Lake volcanic field lies in the northern Coast Ranges, California, ca. 135 km north of San Francisco. The volcanic field consists of lava dome complexes, cinder cones, and maars of basaltic-to-rhyolitic composition. Mount Konocti, a dacitic lava dome on the south shore of Clear Lake, is the largest volcanic feature.
The area has intense gethermal activity, caused by a large, still hot silicic magma chamber about 14 km wide and 7 km beneath the surface. It provides the heat source for the Geysers, the world's largest producing geothermal field on the SW side of the volcanic field. Its geothermal power plants can generate approximately 2000 megawatts, enough to power two cities the size of San Francisco.
The latest volcanic activity happened about 10,000 years ago and formed maars and cinder cones along the shores of Clear Lake, the larges natural freshwater lake in California. Volcanism around Clear Lake is related to the complex San Andreas transform fault system.
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