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Monday, October 04, 2004 - Page updated at 09:56 A.M.

Mount St. Helens poised to erupt

By Hal Bernton
Seattle Times staff reporter

DON RYAN / AP
Mount St. Helens was hazy with blowing ash yesterday from two recent eruptions. Experts say an eruption is probably imminent, within hours or days. They said the biggest potential hazard is an ash plume that might rise to 20,000 feet or more, and air space over the volcano was closed.
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CASTLE LAKE VIEW POINT — Mount St. Helens continued to quiver and quake yesterday in a probable prelude to a magma-powered eruption.

"There's a lot of energy, and it's relatively close to the surface," said Peter Frenzen, chief scientist for the Mount St. Helens National Volcanic Monument. "The big question still is how big of an event will occur."

Scientists are tackling that question with an increased sense of urgency, sending crews to the mountain yesterday to install new, more sensitive equipment and flying over the crater to sample the air.

Yesterday, the U.S. Geological Survey (USGS) continued to post a Level Three alert. That is the highest level of a volcano advisory, and it indicates an eruption is probably imminent, within hours or days.

A no-fly zone has been imposed over the volcano, though the closure won't affect any commercial routes, a U.S. Forest Service spokeswoman said.

The volcanic activity yesterday included more swarms of powerful earthquakes and harmonic tremors that began around 3 a.m. and continued for some 25 minutes. Such tremors indicate an upward movement of magma or explosive gases. They were considerably shorter than Saturday's noon-hour tremors but still another strong sign of a probable eruption.

"They [the tremors] were coming in at about two beats per second, and you could almost imagine the whole volcano rattling in cadence," Frenzen said.

After the tremors stopped, there was a brief period of relative calm. Then, the volcano's plumbing regained pressure, and earthquakes resumed at the rate of one to three per minute, indicating that magma or gas was cracking underground rock.

JAMES BRANAMAN / THE SEATTLE TIMES
A helicopter flies near Mount St. Helens' crater yesterday as a series of rockfalls, caused by quakes and tremors, raises clouds of dust. The quakes indicate an upward movement of magma or explosive gases.
Trail of steam

Volcanic activity also became visible to the naked eye as a star-studded, moonlit night sky gave way to the pink glow of yesterday's dawn. As the mountain's massive interior crater became visible, so, too, did a lacy trail of steam that stretched out to the northeast for several miles.

As the day wore on and the quakes rocked the crater, rockfall after rockfall tumbled down the steep interior walls to kick up clouds of dust.

The volcano is being monitored by a joint command post that now includes federal, state and county officials. As of yesterday, scientists said the biggest potential hazard is an ash plume that might rise to 20,000 feet or more. That could pose a risk to aviation but would be more of an irritant than a danger to people on the ground, according to the scientists.

There's also a smaller possibility of the explosions melting portions of a crater glacier. That could trigger a mudslide that would move into the Upper North Fork of the Toutle River Valley, according to Jim Vallance, a USGS geologist. But it is not likely to pose a risk to downstream residents.

An explosive ash and rock eruption many times more powerful than the small Friday eruption is possible, they said. But it would be far less potent than the May 18, 1980, blast that killed 57 people.

Observatory closed

The prospect of an ash cloud, along with the risk of hurled rocks, prompted a Saturday decision to close the Johnston Ridge Observatory, some five miles north of the mountain on Highway 504. It will remain closed indefinitely.

The U.S. Forest Service yesterday closed more hiking trails as well as some Forest Service roads south of the mountain as a precautionary measure.

But Highway 504, which traverses the Toutle River Valley north of the mountain, remained open to Mile Post 43. Thousands of people journeyed east up the highway, pulling off along waysides and creating capacity-crowd jams at the Coldwater Ridge Visitor Center, which offers sweeping views of the crater.

It got to the point that state Department of Transportation officials urged drivers to stay away from Highway 504.

Backups have been as long as a mile as drivers who haven't heeded warnings wait until the last minute to turn around at the end of the road.

Frenzen said any ash cloud would most likely head to the northeast and not fall on the volcano watchers. But if winds blew ash toward Highway 504, the biggest danger would be panicking crowds, not the ash itself, Frenzen said.

Scientists from the USGS have been working around the clock to share information they have gathered about the volcano's actions of the past week. They also talked with experts at the University of Washington and elsewhere.

One of the most significant findings came from a Saturday flight over the crater. For the first time, instruments detected significantly elevated levels of carbon dioxide, a sign of explosive gas working its way to the surface, Vallance said.

If an eruption occurs, that gas could help fling magma into the air. But some magma also might ooze into the crater. Still, it was expected to be much cooler than the glowing orange magma that rises out of Hawaiian volcanoes, Vallance said. But it still might glow faintly in the dark.

Scientists yesterday planned more flights over the mountain to check for volcanic gases. Teams also were scheduled to work on the ground to improve Global Positioning System equipment that helps detect any change on the mountain's outer flanks. Such deformations pushed out a portion of the mountain's north side before the May 18, 1980, eruption. And that set the stage for a deadly lateral blast.

So far, no such deformation has been detected in recent days on the mountain flanks, according to Vallance.

Inside the crater, scientists have detected a crack in the top of the 925-foot lava dome, which acts as a kind of giant plug. The crack is near a vent that opened in the crater glacier after Friday's blast.

But dome-monitoring equipment and the plywood shack that housed it were destroyed by Friday's eruption. So there now is no precise way to gauge movement of the crater's lava dome. And it is considered far too dangerous to venture back into the crater to install new equipment, according to Vallance.

"No one feels that comfortable being on the ground right now," he said.

Seattle Times staff reporter J. Patrick Coolican contributed to this report.

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com

Copyright © 2004 The Seattle Times Company

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