Coso Geothermal Field
China Lake Naval Weapons Facilltity, California
The Coso Geothermal Field is nestled in the western edge of the Basin and Range Province. This geothermal field is evidence of recent volcanism due to crustal extension. There have been intermittent lava flows here for the past 6 million years. Bimodal volcanism, the eruption of both high-silica lavas and mafic lavas, is also displayed by the topography. In the past 1 million years 38 rhyolite domes and flows, as well as basalt flows from 14 different vents have shaped the land. Many of these rhyolite domes are found within tuff-ring craters. In addition, obsidian can be seen at most extrusions, suggesting that the rhyolite is of the high-silica variety. A basalt flow dated to 40,000 years ago is the youngest feature that has been dated in the Coso Geothermal Field.The host rock for the geothermal activity was granite (quartz diorite/ granite diorite). Scientists originally believed a magma body to be 12 km below, but now it is thought that the magma body is only 5 km. Our guide described the area of the China Lake to be as big as Rhode Island.
Scientists speculate that there will be more volcanic activity here. The source of water within the geothermal system is derived from rain and snowmelt from the Sierra Nevada Mountains. The water moves through the fractures in the granitic basement rock. The geothermal plant consists of 85 active wells. These wells are drilled from anywhere between 2,500 feet and 13,000 feet. Heated water consists of about 70% of the volume while steam is about 30%. The temperature of the water varies from 375- 425 degrees Fahrenheit. About 15%- 20% of the mass in the geothermal system is lost continually, which gives the need for more water in the aquifer to stabilize ground subsidence. The subsidence at Coso is relatively small to other geothermal sites.
The most captivating scene at the Coso Geothermal Field is the mud volcanoes. The ground shaking below your feet reminds one of the catastrophic processes that are possible within these heavily faulted landforms. The steam rising up from these huge bubbling pots of mud is amazing. Mud splashes as the bubbles break and gas is released. The ground around the mud volcanoes is colored yellow by sulfur. Native Americans still visit the site today for religious and medicinal purposes as they have been doing for thousands of years.
References and Links:Books
Armstead, H. Christopher H., Geothermal Energy. E. & F.N. Spon Ltd., New York, 1983.
Bierman, Sheldon L., Geothermal Energy in the Western United States. Praeger Publishers, New York , New York, 1978.
Burman, Edward R., Geothermal Energy. Noyes Data Corp., Park Ridge, NJ, 1975
Meadows, Katherine F., Geothermal World Directory. Glendora, California. 1974.Web Sites
http://geothermal.id.doe.gov
http://www.eren.doe.gov/geothermal
http://www.geothermal.org/index.html
http://www.geotherm.org
http://rredc.nrel.gov/geothermal
http://ucsusa.org/energy/index.html?brief.geothermal.html
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Created by: Scott Schoefernacker
Last Updated: December 2003