Long-term outlook for volcanic activity in Long Valley caldera

When measured in the time-scale of a human lifetime, volcanic eruptions or destructive earthquakes are infrequent events. How does this ongoing geologic activity affect those who live in or visit this area of spectacular eastern Sierra scenery?

The best guide to the future behavior of a volcano or volcanic system is its past behavior. Geological studies of Long Valley Caldera and the Mono-Inyo Craters volcanic chain indicate that:

• Future eruptions are more likely to occur somewhere along the Mono-Inyo Craters volcanic chain than from the resurgent dome or south moat area within the caldera.
• In the absence of unrest (earthquake swarms, ground deformation, gas emissions, and fumarole activity), the odds of an eruption occurring in any given year along the chain are one in a few hundred (comparable to the odds for a great [magnitude 8] earthquake along the San Andreas fault in coastal California).
• Unrest can temporarily increase the odds of an eruption, depending on the nature, intensity, and location of the unrest.
• Future eruptions are likely to be explosive in style but small to moderate in size. For the Mono Chain, any eruption would probably include both. For the Long Valley Caldera and Mammoth area, the most likely eruption is a lava fountaining eruption that builds a scoria cone and feeds lava flows.
• The odds that a small eruption somewhere along the chain will have a significant impact on any specified place along the chain are roughly one in a thousand in a given year.
• Larger eruptions are possible but less common (and thus less likely) than smaller ones (true for most volcanoes).
• Massive eruptions of the size that accompanied formation of Long Valley Caldera 760,000 years ago are extremely rare (none have occurred during the period of written human history). Scientists see no evidence that an eruption of such catastrophic proportions might be brewing beneath Long Valley caldera.

Additional Information About the Outlook at Long Valley Caldera

Looking at the history of volcanic eruptions at any volcano helps scientists understand what might happen in the future at any volcano. Find out more about the recent eruptions in the Long Valley region.

All but three of the 20 or so eruptions over the past 5,000 years at Long Valley Caldera have been explosive in nature. Those three were of the effusive, Hawaiian type (the Red Cones eruptions south of Mammoth Mountain about 5,000 year ago, the Negit Island eruption about 2,000 years ago, and the Paoha Island eruption just 300 years ago). All have been small to moderate in scale. So what type of eruptions can we expect at Long Valley Caldera?