The Lassen Geothermal System

Abstract

The Lassen geothermal system consists of a central vapor-dominated reservoir underlain by hot water that discharges peripherally at lower elevations. The major thermal upflow at Bumpass Hell (elevation 2,500 displays numerous superheated fumaroles, one of which in 1976 was Gas geothermometers from the fumarole areas and water geothermometers from boiling waters at Morgan Hot Springs (elevation 1,530 m; 8 km south of Bumpass Hell) and from waters in a well 12 km southeast of Bumpass Hell both indicate 230-240?C for the deep thermal water. With increasing distance from Bumpass Hell, gases are progressively depleted in relative to C02 and owing to oxidation of to pyrite, sulfur, and sulfates and to dilution with atmospheric N2. ratios and degree of superheat of fumaroles can be explained by mixing of steam of maximum enthalpy (2,804 J with nearsurface water and with the condensate layer overlying the vapor-dominated reservoir.