Mount St. Helens Steams During Slight Quakes

Vancouver, Washington
Associated Press

January 17, 2008

Steam seeping from a fracture atop the lava dome in Mount St. Helens' crater during the mountain's first noteworthy seismic activity since 2004 caught the attention of scientists this week.

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," said Cynthia A. Gardner, the scientist in charge of the U.S. Geological Survey's Cascades Volcano Observatory.

Steam

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 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 (600 square kilometers) of forest and killing 57 people.

(See map of Washington State.)

"Surprises"

The last noteworthy tremor at the volcano lasted 55 minutes on October 2, 2004, and was much more powerful than this week's and caused a hasty evacuation of the Johnston Ridge Observatory five miles (eight kilometers) 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.

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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