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ABSTRACT: Significant Role of Climatic Trends on Hydrothermal Activity Coso Hot Springs, California

Ben E. Lofgren

The hydrothermal features of Coso Hot Springs have attracted visitors for 130 yr and scientific investigators for two decades. In 1978, anticipating effects of major geothermal developments nearby, the Naval Weapons Center (NWC) initiated a comprehensive monitoring program at a dozen hydrothermal sites in the Coso Hot Springs area.

Nine years of monitoring preceded power production in the nearby Coso geothermal field in July 1987. During this period, steam was rising from numerous vents and gently boiling mud pots. Local rainfall caused increased boiling activity in several mud pots, with some overflowing during wet periods. Then in August 1988, a year after geothermal power production began, major changes in hot spring activity commenced. Small mud pots and steamers started to grow and coalesce. In March 1989, mud-pot activity became more violent. Many buried wells failed, causing surface activity in other areas to diminish. During ensuing months, large mud cones developed and much of the steam and boiling water occurred in a few major pots.

Because the abrupt changes in hydrothermal activity followed so closely after nearby geothermal production began, the obvious cause has been attributed to geothermal developments. Studies of NWC baseline monitoring data indicate, however, that no effects of geothermal developments have been felt in the hot springs area. Rainfall and barometric effects account for most of the fluctuations in records of the past decade. Early accounts and field evidence suggest similar changes have occurred in the past.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990