The ground at Mount Redoubt rumbled intermittently Tuesday, and the Alaska Volcano Observatory continued to forecast a potential eruption there "within days."
The 10,197-foot peak 100 miles southwest of Anchorage now appears ready to explode for the second time in 20 years, the observatory noted in a mid-day status report.
"A further increase in seismicity is expected to accompany an eruption," the agency said. Observatory staff continue to monitor the volcano 24 hours a day.
If history is a guide, Redoubt should erupt in style, geologists say. Unlike volcanoes in Hawaii, which tend to ooze out slow-rolling lava, volcanoes in Alaska -- Redoubt included -- usually erupt explosively, shooting ash nearly eight miles high.
That's because the gas that's trying to escape the volcano gets blocked, either by a lava dome or thick, syrupy magma -- characteristic of the highly viscous material in Alaska volcanoes -- which increases the power below, AVO geologist Jennifer Adleman said.
"Its pressure keeps building and building. ..."
Then it blows.
Were that to happen around 9 a.m. this morning, the forecast winds would carry the ash plume directly toward Anchorage, according to a chart posted on the Alaska Volcano Observatory Web site Tuesday. The warning prompted both state and city emergency agencies to issue bulletins to residents with advice on how to cope with an ash storm.
Stay inside as much as possible, the Anchorage Office of Emergency Management said. Wear a dust mask or a wet bandana if you venture outdoors. People who wear contact lenses should consider wearing goggles.
Volcanic ash consists of tiny jagged pieces of rock and glass, an advisory posted by the U.S. Geological Survey noted.
"Falling ash can turn daylight into complete darkness. Accompanied by rain and lightning, the gritty ash can lead to power outages (and) prevent communications...."
The last time Redoubt erupted -- over a five-month period that lasted from December 1989 through April 1990 -- the ash plume disrupted international air traffic and coated Anchorage in a thin layer of volcanic dust.
It also sent "pyroclastic flows" of hot gas and rock rushing down the Drift River drainage, turning ice and snow into a fast moving river of mud, which partially flooded the Drift River Oil Terminal on the western shore of Cook Inlet. The state said Tuesday afternoon that the terminal's volcano readiness plan is now in effect.
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By GEORGE BRYSON
gbryson@adn.com