Will There Be a Mammoth Volcanic Eruption
on Mammoth Mountain?
by Amy Wahe

More than 750,000 years ago, a massive volcanic eruption created what is now known as the Long Valley Caldera, located in Eastern California. The Long Valley Caldera is a volcanic depression that is part of a larger seismic network called the Mono-Inyo Craters Volcanic Chain. Of particular concern within this mountain chain is Mammoth Mountain, home to a popular California skiing and vacation community.

Concern for the safety of the thousands of homes and businesses located in Mammoth is growing.

  • What is the likelihood that future eruptions will occur?
  • What effect will future eruptions have on this bustling mountain town and the environment in general?
  • Will an eruption have a negative impact on California's economy?

These questions not only baffle the residents of Mammoth Lakes, but the many scientists who are monitoring the Long Valley Caldera as well.

Predicting volcanic eruptions is no easy task. Although scientist can identify many indicators of an active volcano, predicting when a volcano is going to erupt, or the magnitude of that eruption is difficult at best. Scientists have been monitoring the Long Valley Caldera since 1980, when a series of strong earthquakes (magnitude 6) rocked the area after a long period of geologic stability. These quakes indicated a renewal of volcanic activity in the area, and have led to a rapid increase in geologic research in the area. Mammoth is currently home to one of the largest installations of earth monitoring instruments in the country, if not the entire world.

Since 1980, scientists have continued to monitor the area for indications of a possible eruption. It is believed that geologic activity in the Long Valley Caldera will continue for many years to come. Scientists have identified two indicators of possible eruption; the death of local trees due to carbon dioxide emissions, and "ground deformation". The presence of these indicators in the Mammoth region suggests that the likelihood of a future eruption is slightly elevated. Malcolm Johnston and David Hill of the U.S. Geological Survey (U.S.G.S.) suggest that the future of the Long Valley Caldera "remains problematic". However, worldwide studies of volcano-prone areas, suggest that the type of volcanic unrest observed in the Long Valley Caldera can persist for long periods of time and never result in an eruption.

If a volcanic eruption were to occur, scientists predict that it would be similar to previous eruptions in the area, which have typically been small, but explosive in nature. The "typical" volcano in the last 5000 years has been a "narrow, tongue-like pyroclastic flow", which produces hot blasts of ash and fluid lava extending about 5 miles. Research suggests that during the last 5000 years, an eruption has occurred every 220 to 700 years. The last eruption that took place in the area occurred 550-650 years ago.

The U.S. Geological Survey predicts that the likelihood of an eruption occurring in any given year is only about 1%. Secondly, an eruption is unlikely to reach the main population center of the Mammoth community. In any event, the U.S. Geological Survey and the California Office of Emergencies have prepared for this unlikely event by establishing procedures for monitoring and informing the public of an eruption and emergency procedures should one occur.


Reich, Kenneth. On Shaky Ground. Los Angeles Times January 22, 1998.

Volcanic and Geologic Terms. Volcano World: http://volcano.und.nodak.edu/vwdocs/glossary.html.

David P. Hill, Roy A. Bailey, Michael L. Sorey, James W. Hendly II, and Peter H. Stauffer. Living With a Restless Caldera- Long Valley, California. U.S. Geological Survey Fact Sheet 108-96, revised 1997. http://geopubs.wr.usgs.gov/fact-sheet/fs108-96/

Monitoring Volcanic Unrest at Long Valley Caldera. U.S. Geological Survey Volcano Hazards Program. http://quake.wr.usgs.gov/VOLCANOES/LongValley/index.html

Long-Term Outlook for Volcanic Activity in Long Valley Caldera and the Inyo-Mono Craters Volcanic Chain. U.S. Geologic Survey Volcano Hazards Program. http://quake.wr.usgs.gov/VOLCANOES/LongValley/Outlook.html


David P. Hill, Roy A. Bailey, C. Dan Miller, James W. Hendly II, and Peter H. Stauffer Future Eruptions in California's Long Valley Area- What's Likely? U.S. Geologic Survey Fact Sheet 073-97. http://wrgis.wr.usgs.gov/fact-sheet/fs073-97/

Long Valley Caldera and Mono-Inyo Craters Volcanic Field, California. Volcano World. http://volcano.und.nodak.edu/vwdocs/site_index.html