Series of Quakes Reported at Mount St. Helens
Pastor Dale Morgan
Series of Quakes Reported at Mount St. Helens *
Jan 16 10:18 PM US/Eastern
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 steam.
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,
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
said.
"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.