Long Valley, California: a Caldera Under Stress

Abstract

Long Valley caldera in east-central California has been the site of intermittent volcanism up until as recently as 550-650 years ago, and since 1980 has experienced active seismicity and magmatic inflation. Such processes have caused changes in the caldera's hydrothermal system as has fluid production for geothermal energy development. A program of hydrologic and chemical monitoring by the U.S. Geological Survey has been in effect since 1982 to detect and quantify changes in hot spring discharge, chemistry and isotopic content of springs and fumaroles, and temperature and pressure in wells. The results of this monitoring have lead to increased understanding of the hydrothermal system and the level of natural variability within the system, and documented decreases in hot spring flow at one site where fluid is produced for geothermal development.