Geophysical characterization of the Northwest Geysers geothermal field, California

Journal of Volcanology and Geothermal Research
By: , and 



The Clear Lake Volcanic Field in northern California is the youngest and northern-most part of a long-lived volcanic system that has produced recent (~10 ka) eruptions. Adjacent to the Clear Lake Volcanic Field is the worlds largest energy producing geothermal field, The Geysers. The hottest part of The Geysers geothermal field is in the northwest where temperatures reach ~400 C at 3 km depth. Low permeability, high thermal gradients, and low steam saturation prescribed development of an enhanced geothermal system (EGS) in the Northwest Geysers to increase energy producing capacity. Though the Northwest Geysers is known to be the hottest part of the field, geophysical methods have failed to adequately image any inferred heat source. This project aims to image the heat source of the Northwest Geysers using newly collected gravity and magnetotelluric (MT) measurements. Gravity data were jointly modeled with existing magnetic data along a two-dimensional profile aligned with an existing geologic cross-section. The key feature of the potential field model is a low-density, low-susceptibility body at 5 km depth (bmsl) under the EGS. MT data were modeled in three-dimensions to characterize subsurface resistivity structure, where the upper 3 km of the resistivity model agrees well with existing data. Lithologic and steam saturation are estimated from modeled resistivity values using existing geophysical data. Below 3 km depth (bmsl), the resistivity model images a possible young intrusion under the EGS. A possible zone of partial melt (<5%) below 7 km depth (bmsl) in the northwestern part of the field is also imaged which extends northeast towards the main part of the Clear Lake Volcanic Field.

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Publication type Article
Publication Subtype Journal Article
Title Geophysical characterization of the Northwest Geysers geothermal field, California
Series title Journal of Volcanology and Geothermal Research
DOI 10.1016/j.jvolgeores.2020.106882
Volume 339
Year Published 2020
Language English
Publisher Elsevier
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 106882, 17 p.
Country United States
State California
City Twin Lakes, Glenview
Other Geospatial Southern Clear Lake
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