Long-Term Outlook for Volcanic Activity in Long Valley Caldera
and the Mono-Inyo Craters Volcanic Chain
The area of eastern California that includes Long Valley Caldera
and the Mono-Inyo Craters volcanic chain has a
long history of geologic activity that
includes both earthquakes and volcanic eruptions. This activity is
likely to continue long into the future. Geologic processes proceed
at a ponderous pace, however, and 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.
Current, relatively low levels of unrest increase the odds of an
eruption only slightly.
- Future eruptions are likely to be explosive in style but small
to moderate in size (Click here for a note on
eruption sizes.) Effusive (non-explosive), Hawaiian style
eruptions are also possible but somewhat less likely.
- 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
More 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 prehistoric
eruptions at Long Valley Caldera and how these eruptions affect the
odds of a future eruption.
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 250 years
ago). All have been small to moderate in scale. So
what can we expect if an eruption does occur
at Long Valley Caldera?
Intense unrest can temporarily increase the odds that an eruption
will follow. The U.S. Geological Survey's monitoring program is
designed to recognize the sort of unrest that indicates a significant
increase in the chances of an imminent eruption. Find out
how unrest affects the chances of another
volcanic eruption at Long Valley.
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U.S. Department of the Interior, U.S. Geological Survey, Menlo Park, California, USA
URL http://lvo.wr.usgs.gov/Outlook.html
Contact: Long Valley Web Team
Last modification: 14 October 1999 (SRB)