Report on Long Valley (United States) — March 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 3 (March 1983)
Managing Editor: Lindsay McClelland.
Long Valley (United States) Seismicity declines to near background
Please cite this report as:
Global Volcanism Program, 1983. Report on Long Valley (United States) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 8:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198303-323822.
37.7°N, 118.87°W; summit elev. 3390 m
All times are local (unless otherwise noted)
Seismicity continued to decline in the epicentral area of the major January earthquake swarm. Brief bursts of small shocks were occasionally recorded, but by early April, daily earthquake counts were approaching the pre-January background levels of 2-5 events of magnitude greater than or equal to 1 per day.
Geologic Background. The large 17 x 32 km Long Valley caldera east of the central Sierra Nevada Range formed as a result of the voluminous Bishop Tuff eruption about 760,000 years ago. Resurgent doming in the central part of the caldera occurred shortly afterwards, followed by rhyolitic eruptions from the caldera moat and the eruption of rhyodacite from outer ring fracture vents, ending about 50,000 years ago. During early resurgent doming the caldera was filled with a large lake that left strandlines on the caldera walls and the resurgent dome island; the lake eventually drained through the Owens River Gorge. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years. The late-Pleistocene to Holocene Inyo Craters cut the NW topographic rim of the caldera, and along with Mammoth Mountain on the SW topographic rim, are west of the structural caldera and are chemically and tectonically distinct from the Long Valley magmatic system.
Information Contacts: D. Hill, USGS, Menlo Park, CA.