Long Valley Caldera Hydrologic Studies


Hydrologic data format




The USGS monitors springs, streams, wells, fumaroles, and precipitation in Long Valley to study the natural hydrologic variations and the response of the hydrologic system to volcanic and tectonic processes (Howle and Farrar, 1996, Howle and Farrar, 2001, Sorey and Farrar, 1998). The locations of all monitoring sites are shown below. Hydrologic data from key monitoring sites are posted every day on the Long Valley Observatory web site (http://lvo.wr.usgs.gov/HydroStudies.html) allowing to quickly review recent data for real or (faulty) equipment induced anomolies.

Long Valley caldera ground water monitoring network

The USGS Ground-water Monitoring Network in Long Valley is maintained by Chris Farrar (cdfarrar@usgs.gov) and Jim Howle (jfhowle@usgs.gov), Carnelian Bay Field Office, California District, Water Resources Division, USGS.

Hydrothermal System

Long Valley caldera hosts an active hydrothermal system that includes hot springs, fumaroles (steam vents), and mineral deposits (Sorey et al., 1991). Hot springs exist primarily in the eastern half of the caldera where land-surface elevations are relatively low; fumaroles exist primarily in the western half where elevations are higher. Hot springs discharge primarily in Hot Creek Gorge, along Little Hot Creek, and in the Alkalai Lakes area. Springs at the Hot Creek Fish Hatchery contain a small component of thermal water; their slightly elevated temperature (~16°C) is required for operations at the hatchery.

In hydrothermal systems the circulation of ground-water is driven by a combination of topography and heat sources. In Long Valley caldera, flow starts in the west and continues to the southeast around the resurgent dome and then eastward toward Hot Creek and Crowley Lake. Reservoir temperatures in the volcanic fill decline from 230°C near the Inyo Craters to 50°C near Crowley Lake due to a combination of heat loss and mixing with cold water.

The recently completed Long Valley Exploratory Well (http://lvo.wr.usgs.gov/LVEW.html), which was drilled on the resurgent dome to a depth of 9,832 feet (2,997 meters), has provided new information on the history of hydrothermal activity in the caldera, and will be used to study heat and fluid circulation in the region.

Geothermal Power Development

Wells drilled on the southwest side of the resurgent dome at Casa Diablo tap into the caldera's hydrothermal system by pumping hot water (170°C) to supply three hydrothermal power plants that generate about 40 megawatts of electricity. Using a binary technology, a secondary fluid (isobutane) is heated by the pressurized geothermal water, vaporized, and then run through the generating turbines. Cooled geothermal water is reinjected underground.

The hydrologic monitoring program has detected changes in the hydrologic system caused by geothermal development and variations in precipitation and recharge (Howle and Farrar, 1997). For example, we have delineated decreases in thermal-spring discharge at sites within about 5 km to the east of Casa Diablo that are caused by subsurface pressure declines at the geothermal well field. No changes have as yet been detected in the springs in Hot Creek gorge. There has also been an increase in steam discharge at Casa Diablo and sites farther west due to increased boiling in the geothermal reservoir caused by geothermal production.

Causes of Variations in the Hydrologic System:


Howle, J.F. and Farrar, C.D., 2001. Hydrologic data for Long Valley Caldera, Mono County, California, 1994-96. Open-File Report - U. S. Geological Survey, Report: OF 00-0230, 155 pp.

Howle, J.F; Farrar, C.D., 1997. Deformation in the Casa Diablo geothermal well field, Long Valley Caldera, eastern California. Open-File Report - U. S. Geological Survey, Report: OF 97-0047, pp.31-35.

Howle, J.F. and Farrar, C.D., 1996. Hydrologic data for Long Valley Caldera, Mono County, California, 1978-93. Open-File Report - U. S. Geological Survey, OF 96-0382.

Sorey, M.L. and Farrar, C.D., 1998. Hydrologic and chemical data from the Long Valley Hydrologic Advisory Committee Monitoring Program in Long Valley Caldera, Mono County, California, 1988-1997. Open-File Report - U. S. Geological Survey, OF 98-0070, 49 pp.

Sorey, M.L., Suemnicht, G.A., Sturchio, N.C., and Nordquist, G.A., 1991, New evidence on the hydrothermal system in Long Valley Caldera, California, from wells, fluid sampling, electrical geophysics, and age determinations of hot spring deposits: Journal of Volcanology and Geothermal Research, v. 48, no. 3-4, p. 229-263.

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