Chance of Mount St. Helens eruption grows

By Sandi Doughton and Ian Ith
Seattle Times staff reporters

STEVE RINGMAN / THE SEATTLE TIMES Television news trucks are clustered on an overlook near the Johnston Ridge Observatory, with the crater of Mount St. Helens in the background, in case of an eruption.

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The most likely event would be a small explosion that flings rocks up to three miles away from the crater and sends a plume of ash thousands of feet into the sky, said volcanologist Cynthia Gardner of the U.S. Geological Survey's Cascades Volcano Observatory.

But it wouldn't approach the magnitude of the 1980 eruption that blew out the mountain's entire northern face and killed 57 people.

"And there's still a significant chance it will peter out," added USGS seismologist Seth Moran.

It's also possible the volcano may be embarking on another period of prolonged activity, similar to the mid-1980s, when several small lava flows built up the dome that now sits in the middle of the crater, Moran said.

"It could go on for quite a while."

Gardner dispelled rumors that Mount Rainier and other Cascade volcanoes in Washington are also reawakening.

"Mount St. Helens is the only one that's active," she said. Though they work in similar ways, there's no evidence the volcanoes influence each other. "They aren't connected," she said.

	STEVE RINGMAN / THE SEATTLE TIMES Jonathan Nitkowski of Woodland, Cowlitz County, photographs pictures showing the mountain before and after the 1980 eruption.

Nor are the occasional bursts of steam from the crater an indication of an imminent eruption, Gardner said.

Small, shallow earthquakes started rattling the volcano a week ago. Initially less than magnitude one, the temblors have gradually increased in size. Last night and early this morning, some reached magnitude 3.3, Moran said. The rate remains high, with three to four earthquakes occurring every minute.

But the lava dome apparently hasn't swelled significantly overnight, which indicates that magma is probably not migrating toward the surface, Moran said. Gas measurements over the crater also show no evidence of magma movement.

Without fresh magma entering the system, any eruption will almost certainly be modest, the scientists said.

Because the area around the volcano is virtually uninhabited, the risk to human life or property is low, said USGS volcanologist Dan Miller. The closest development is the Johnston Ridge Observatory five miles from the crater; it remained open yesterday.

Jonathan Nitkowski of Woodland, Cowlitz County, photographs pictures showing the mountain before and after the 1980 eruption.

"If an eruption were to occur at Mount St. Helens, it's one of the better places in the country for it to happen," Miller said.

Yesterday, the U.S. Geological Survey raised the alert level at the volcano from Level One, which means the volcano has entered a period of unrest, to Level Two, which means an eruption is likely. Level Three, the highest level, means an eruption is imminent or under way. The state yesterday activated its Emergency Operations Center at Camp Murray, south of Tacoma, to monitor the situation and assist local government if needed.

A single sensor installed in the crater Monday measured a bulge of slightly less than two inches in the lava dome, a possible indicator of moving magma. But scientists who flew over the crater yesterday didn't detect the gases that would be released if fresh magma was pushing toward the surface.

	STEVE RINGMAN / THE SEATTLE TIMES With Mount St. Helens behind the clouds in the background, Jolahna Gamblewood, a Forest Service Ranger, talks to visitors yesterday at the Johnston Ridge Observatory about the 1980 eruption.

The hardened lava dome forms a kind of a plug in the volcano's plumbing, Moran said.

In 1998, fresh magma moved into the system, rising to within about a mile of the surface, but not escaping.

One explanation for what's happening now is that rainwater percolated into the dome, reacting with hot rock to cause cracking, Moran said. That cracking may have created pathways to allow some of the magma from 1998 to begin moving again.

Yesterday, the U.S. Forest Service, which manages most of the land that surrounds the volcano, closed the Mount Margaret area north of the peak to overnight camping.

"It's a remote area, and we didn't want to have people out in the backcountry should conditions change," spokesman Tom Knappenberger said. Last weekend, shortly after the earthquake swarms began, the agency banned mountain climbers from the volcano's upper flanks and closed hiking trails on the north side.

The Washington Department of Natural Resources closed to the public all of its lands within a 12-mile radius of the volcano, and pulled all of its staff and contractors out of the area. The agency also closed the Merrill Lake Campground.

But at Johnston Observatory, a 7-year-old facility with a sweeping view, a steady stream of tourists came and went, apparently undaunted by news of the mountain's reawakening.

Several school groups that had booked field trips to the observatory maintained their schedule, although a few opted to back out, said Gala Miller, chief of interpretation.

"It's more exciting than scary for me," she said. "I have faith that the information we're getting from the geologists is relatively accurate - but then again, things may change tomorrow."

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com

Copyright © 2004 The Seattle Times Company

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