Digital Data Series DDS-81
U.S. Department of the Interior
Gale A. Norton, Secretary
U.S. Geological Survey
Charles G. Groat, Director
1 Dept. of Geophysics, Stanford University, Stanford, CA 94305-2215.
Now at UC Berkeley Seismological
Laboratory, 215 McCone Hall, Berkeley CA
94720-4760. E-mail: email@example.com
2 Branner Earth Sciences Library, Stanford University, Stanford, CA 94305
3 U.S. Geological Survey, 345 Middlefield Rd., MS977, Menlo Park, CA 94025
U.S. Geological Survey, P.O. Box 1360, Carnelian Bay, CA 96140
5 U.S. Geological Survey, Placer Hall, California CSUS,
Sacramento, CA 95819-6129
Long Valley Caldera at a Glance
Fact Sheets about Long Valley Caldera
References about Long Valley Caldera
Landsat image of the Long Valley-Mono Basin Region
The Caldera. 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 the Mono-Inyo Craters volcanic chain.
Volcanic Unrest. In May of 1980, a strong earthquake swarm that included four earthquakes of magnitude 6 or above 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 one 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.