Long Valley Caldera Geothermal and Magmatic Systems

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Conference Paper: Long Valley Caldera Geothermal and Magmatic Systems

Long Valley Caldera in eastern California has been explored for geothermal resources since the 1960s. Early shallow exploration wells (<300m) were located around Casa Diablo near the most prominent hot springs and fumaroles on the southwest flank of the Resurgent Dome (Figure 1). Later deep (±2000m) wells explored the southeastern caldera moat and evaluated lease offerings in and around the caldera's Resurgent Dome. Data from these wells revealed that the principal geothermal reservoir in Long Valley is not located directly beneath the Casa Diablo Hot Springs and is not currently related to the Resurgent Dome. Instead, the hydrothermal system appeared to be more complex with shallow production at Casa Diablo supplied by upflow and outflow from a more extensive deeper geothermal source beneath the western caldera moat. Geothermal development at Casa Diablo occurred in stages under various operating companies. Mammoth Pacific LP, a subsidiary of Ormat Nevada Inc., currently owns the project and generates 40 Mw (gross) from three power plants utilizing 6 production wells and 5 injection wells. Until 2005, production of ~630 L/sec (~10,000 gal/min) of moderate temperature (170oC) fluids for the geothermal plants was limited to ~0.7 km2 (~165 ac) around Casa Diablo from shallow wells (<200m) completed in permeable Early Rhyolite eruptive units on the southwestern edge of the Resurgent Dome. MPLP drilled deeper (~450m) production wells in 2005 in the southwest caldera moat around Shady Rest in a development area that Ormat refers to as Basalt Canyon. The deeper west moat wells produce 185°C fluids from deep Early Rhyolite units and the upper part of the Bishop Tuff. In 2006, an average of 126 L/sec (2000 gal/min) of higher temperature brine from the Basalt Canyon wells began to be piped 2.9 km to sustain production at the Casa Diablo plants allowing several older shallow wells to be shut in. The deeper hydrothermal system in Long Valley sustains current production levels by supplying additional shallow hydrothermal outflow from Shady Rest to Casa Diablo.

Gene A. Suemnicht

NGA Long Valley Field Trip, July 5-7, 2012; {{{ConferencePlace}}}
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; 07/05/2012

National Geothermal Academy, 2012

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Gene A. Suemnicht. 2012. Long Valley Caldera Geothermal and Magmatic Systems. In: Long Valley Caldera Field Trip Guide. NGA Long Valley Field Trip, July 5-7, 2012; 07/05/2012; (!) . (!) : National Geothermal Academy; p. 23