Magmatic unrest beneath Mammoth Mountain, California

D.P. Hill; S. Prejean

doi:10.1016/j.jvolgeores.2005.03.002

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Magmatic unrest beneath Mammoth Mountain, California

D.P. Hill·S. Prejean

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Abstract

Mammoth Mountain, which stands on the southwest rim of Long Valley caldera in eastern California, last erupted ∼57,000 years BP. Episodic volcanic unrest detected beneath the mountain since late 1979, however, emphasizes that the underlying volcanic system is still active and capable of producing future volcanic eruptions. The unrest symptoms include swarms of small ( M ≤ 3) earthquakes, spasmodic bursts (rapid-fire sequences of brittle-failure earthquakes with overlapping coda), long-period (LP) and very-long-period (VLP) volcanic earthquakes, ground deformation, diffuse emission of magmatic CO 2 , and fumarole gases with elevated 3 He/ 4 He ratios. Spatial-temporal relations defined by the multi-parameter monitoring data together with earthquake source mechanisms suggest that this Mammoth Mountain unrest is driven by the episodic release of a volume of CO 2 -rich hydrous magmatic fluid derived from the upper reaches of a plexus of basaltic dikes and sills at mid-crustal depths (10–20 km). As the mobilized fluid ascends through the brittle–plastic transition zone and into overlying brittle crust, it triggers earthquake swarm activity and, in the case of the prolonged, 11-month-long earthquake swarm of 1989, crustal deformation and the onset of diffuse CO 2 emissions. Future volcanic activity from this system would most likely involve steam explosions or small-volume, basaltic, strombolian or Hawaiian style eruptions. The impact of such an event would depend critically on vent location and season.

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Journal of Volcanology and Geothermal Research Article

Source-reported bounding extent: 37.617494852086566° to 37.64366515163273° latitude; -119.0544605255127° to -119.00570869445801° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeX RIS

D.P. Hill, S. Prejean. 2005. Magmatic unrest beneath Mammoth Mountain, California. https://doi.org/10.1016/j.jvolgeores.2005.03.002

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