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Scientists eye activity at Oregon volcano
Published 3/31/2002 7:18 PM


MENLO PARK, Calif., March 30 (UPI) -- Ground near the long-dormant Three
Sisters volcano in the central region of Oregon's Cascade Mountains has
risen approximately 4 inches (100 millimeters) in a 6 by 12 mile (10 by 20
km) parcel since 1998, meaning that magma, underground lava, has flowed into
the area, according to a team of researchers from the U.S. Geological
Survey.

"It hasn't erupted in about 1,500 years, so it's a truly dormant volcano.
Yet there's something going on there," said geologist Charles Wicks Jr.,
lead author of a report in the American Geophysical Journal.

"Right now in the Cascades, the only volcano that we know is restless is
Three Sisters, based on the deformation," said co-author, geologist Daniel
Dzurisin at the USGS Cascade Volcano Observatory in Vancouver, Wash.

The researchers said it's far too early to tell if this swelling and
movement of magma presages a volcanic eruption. It might simply "freeze
out," said Wicks, meaning the magma flow might simply stop.

The groundswell was observed by satellite radar images, a new technique that
Dzurisin said would help scientists track such deformations.

"We now have a tool that allows us to see this kind of deformation around
volcanoes, which we've suspected for a long time. But in the past we haven't
been able to observe it unless there was accompanying seismicity," said
Dzurisin, referring to the earthquakes that occur when the magma breaks
through the rocky crust prior to eruptions. Such quakes are often a warning
of an impending eruption.

"As far as I know this type of observation hasn't been made any other place.
We don't know if this type of uplift occurs fairly frequently at similar
types of places around the world. This type of thing may be relatively
common, but we don't know," said University of Washington geophysicist
Stephen Malone, who is familiar with the finding but is not connected with
the published research.

He noted that geologists are installing seismometers in the area to monitor
for earthquakes.

While the Three Sisters is only about 70 miles (130 kilometers) from Mt. St.
Helens, which erupted in 1980, there is no direct physical connection
between the two. The Cascades are volcanic because the Pacific tectonic
plate slides under the North American plate and is melted by the heat of the
Earth's interior, thus producing magma that rises to the surface.

While geologists say that tracking such groundswells is important for basic
understanding of the way volcanoes work, there are important practical
benefits as well.

"Ultimately the goal is mitigate volcanic hazards, and the way we can do
that is to understand the processes that lead up to eruptions better. We
hope that by being able to see ground deformation like this we might be able
to extend the warnings that we might give," said Dzurisin.