Small Quake Reported at Mount St. Helens|
VANCOUVER, Wash. (AP) — Steam seeping from a fracture atop the lava dome in
Mount St. Helens' crater and the mountain's first noteworthy seismic activity
since 2004 have caught scientists' attention this week as signs that something
is moving inside it.
While the likelihood of a major eruption seemed low, scientists have quit
venturing into the volcano's crater and are checking the monitoring equipment
along St. Helens' flanks.
"We're just being cautious. It's not that we're anticipating any activity,"
Cynthia A. Gardner, scientist in charge of the U.S. Geological Survey's Cascades
Volcano Observatory, said Wednesday.
Geologist John S. Pallister was flying over the volcano in southwestern
Washington on Sunday when he spotted the steam.
"It was interesting enough to take some pictures," said Pallister, a private
pilot who works in the hazards section of the volcano observatory.
After landing, he learned that a magnitude-2.9 earthquake had registered on
seismographs at an observatory in Vancouver. That was followed by a small tremor
that lasted nearly an hour and a half, an unusually long period, punctuated by a
second quake of magnitude 2.7 — all in the same period in which he saw the
Tiltmeters also registered alternate ground swelling and deflation near the
lava dome, which has been growing in the crater since fall 2004.
All are typical signs that magma, superheated gases or both are moving
through conduits beneath St. Helens, which blew its top with devastating force
on May 18, 1980, leveling 230 square miles of forest and killing 57 people.
The last noteworthy tremor at the volcano lasted 55 minutes on Oct. 2, 2004,
and was much more powerful, registering on seismometers from Bend, Ore., to
Bellingham and causing a hasty evacuation of the Johnston Ridge Observatory five
miles north of the crater.
No evacuations had been ordered by Wednesday, because the seismic activity
had slowed down.
The precise cause of the recent activity was not entirely clear, Gardner
"The settling of the growing lava dome might have caused some fracturing and
might have changed the subsurface openings so that water was either being
squeezed out of openings or opening new areas," he said Tuesday.
The last precise measurements, drawn from images in July, indicated the
latest eruptive phase has pumped 123 million cubic yards of material into the
crater. The rate has slowed considerably, but the episode Sunday showed that
could change at any time, Pallister said.
"It's still got some surprises," he said.
Original article: Google - AP
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