Evolution and present state of the hydrothermal system in Long Valley caldera ( USA).

Hydrothermal activity was more intense in the past and probably involved fluid circulation to depths of several km or more with heat supplied by the Long Valley magma chamber. The present-day hydrothermal system in Long Valley appears to consist of 2 principal zones in which hot water flows laterally from W to E at depths of less than 1 km within and around the resurgent dome. Maximum measured temperatures within these zones are near 170oC, but esimates from chemical geothermometers and extrapolation of a high-temperature gradient measured in a recent drill hole indicate that a source reservoir at temperatures near 240o may exist at greater depths within the Bishop Tuff beneath the W moat. -from Author