MONITORING THE HYDROTHERMAL SYSTEM IN LONG VALLEY CALDERA, CALIFORNIA.

An ongoing program to monitor the hydrothermal system in Long Valley for changes caused by volcanic or tectonic processes has produced considerable data on the water chemistry and discharge of springs and fluid temperatures and pressures in wells. Changes in hot spring chemistry that have been recorded probably relate to interactions between the variations in the quantity of liquid and gas discharged. Stable carbon isotope data are consistent with a carbon source either from the mantle or from metamorphosed carbonate rocks. Continuous and periodic measurements of hot spring discharge at several sites show significant coseismic and aseismic changes since 1980.