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Long Valley Supervolcano

Near the Nevada border

 

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Long Valley Supervolcano
Credit USGS


Long Valley Supervolcano

Long Valley, Calif., near the Nevada border
Volcano Number:        120314-A
Volcano Type: Caldera
Volcano Status:           Pleistocene-Fumarolic
Last Known Eruption:            Pleistocene
Summit Elevation:      3390 m            11,122 feet
Latitude:         37.70N           3742'0"N
Longitude:      118.87W        11852'0"W

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.
 

Long Valley Caldera Boundaries
Credit USGS

Long Valley Caldera at a Glance

Long Valley Caldera is a 15- by 30-km oval-shaped depression located 20 km south of Mono Lake along the east side of the Sierra Nevada in east-central California. This area of eastern California has produced numerous volcanic eruptions over the past 3 million years, including the massive caldera-forming eruption 760,000 years ago. The most recent eruption occurred just 250 years ago in Mono Lake at the north end of Mono-Inyo Craters volcanic chain.  

Volcanic Unrest

In May of 1980, a strong earthquake swarm that included four magnitude 6 earthquakes struck the southern margin of Long Valley Caldera associated with a 25-cm, dome-shaped uplift of the caldera floor. These events marked the onset of the latest period of caldera unrest that continues to this day. This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera (the resurgent dome) accompanied by changes in thermal springs and gas emissions.        

USGS Monitoring

In 1982, the U.S. Geological Survey under the Volcano Hazards Program began an intensive effort to monitor and study geologic unrest in Long Valley caldera. The goal of this effort is to provide residents and civil authorities in the area reliable information on the nature of the potential hazards posed by this unrest and timely warning of an impending volcanic eruption, should it develop.

Most, perhaps all, volcanic eruptions are preceded and accompanied by geophysical and geochemical changes in the volcanic system. Common precursory indicators of volcanic activity include increased seismicity, ground deformation, and variations in the nature and rate of gas emissions.        

Text and Maps from USGS
http://lvo.wr.usgs.gov
 

Credit: NASA, The Discovery Channel, The Smithsonian Institute, USGS

Credit also to:
http://www.solcomhouse.com/longvalley.htm

Thanks to Stephanie Relfe for this link

 

 

 
 



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