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Contact: Andy Fell
[email protected]
530-752-4533
University of California – Davis
IMAGE:
Rocks ejected from Mt. Hood show that the magma under the volcano has been liquid enough to erupt for less than 10 percent of the last 20,000 years. If generally…
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Forecasts of when a volcano is ready to erupt could be a little closer thanks to work by
geologists at the University of California, Davis, and Oregon State University published online Feb.
16 in the journal Nature.
For an eruption to occur, the magma, or molten rock under the volcano must be sufficiently
mobile to erupt.
“The question is, what percentage of time is the magma in an eruptible state?†said Kari
Cooper, associate professor in the Department of Earth and Planetary Sciences at UC Davis and lead
author on the paper.
“People think about there being this big reservoir of liquid magma under a volcano, but we
don’t think it’s in that state all the time,†she said.
The mobility of the magma depends on the amount of crystallization: When it is more than
about 50 percent crystalline, it becomes immobile. Crystallization, in turn, depends on the
temperature of the rock.
Until now, volcanologists have not known how common it is for magma to be crystalline
compared to being mobile and eruptible. The new work shows that at least for Mount Hood, Ore., the
magma is mobile less than 10 percent, and perhaps as little as 1 percent of the time.
Cooper and Adam Kent, professor of geology at Oregon State University, studied rocks ejected
from previous eruptions at Mount Hood. By analyzing both radioactive isotopes and the distribution
of trace elements, they were able to reconstruct the history of the rocks and the conditions to
which they had been exposed before they were erupted from the volcano.
VIDEO:
UC Davis volcanologist Kari Cooper talks about new studies of the magma reservoir under Mt. Hood, which could lead to a better understanding of volcanic activity and when volcanoes are…
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The results mean that volcanologists might be able to better assess when a volcano is ready
to erupt by using seismic or other remote imaging to look for mostly liquid magma, Cooper said. If
eruptible magma is indeed relatively rare, then when it does appear, the risks of an eruption are
higher, she said.
Mount Hood is so far the only volcano studied in detail using these techniques. A preliminary
survey of data from similar volcanoes around the world shows that they likely follow a similar
pattern to Mount Hood, with mobile, “eruptible†magma only being present a small proportion of the
time. Cooper and Kent plan further studies to see if these discoveries are widely applicable or
unique to Mount Hood.
The work was funded by the National Science Foundation.
About UC Davis
For more than 100 years, UC Davis has been one place where people are bettering humanity and
our natural world while seeking solutions to some of our most pressing challenges. Located near the
state capital, UC Davis has more than 33,000 students, over 2,500 faculty and more than 21,000
staff, an annual research budget of over $750 million, a comprehensive health system and 13
specialized research centers. The university offers interdisciplinary graduate study and more than
100 undergraduate majors in four colleges Agricultural and Environmental Sciences, Biological
Sciences, Engineering, and Letters and Science. It also houses six professional schools Education,
Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.
Additional media contact:
– Kari Cooper, Earth and Planetary Sciences, (530) 754-8826, [email protected] (Cooper is traveling until Feb. 17 and
best reached by e-mail.)
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