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Thursday, September 30, 2004 - Page updated at 12:57 P.M.
Chance of Mount St. Helens eruption grows
The rumblings from Mount St. Helens intensified yesterday, leading federal scientists to raise the volcanic alert level and warn that a small-to-moderate eruption is likely within the next several days.
The event could fling rocks up to three miles from the volcano's crater and spew ash thousands of feet into the air, but it wouldn't approach the magnitude of the cataclysmic 1980 eruption that blew out the mountain's north side and killed 57 people, scientists said.
And because the area around the volcano is virtually uninhabited, the risk to human life or property is low, said volcanologist Dan Miller, of the U.S. Geological Survey's (USGS) Cascades Volcano Observatory. The closest development is the Johnston Ridge Observatory five miles from the crater; it remained open yesterday.
It's also possible the volcanic activity will subside.
"At this point we're saying there's a heightened possibility of an eruption. We're not guaranteeing you an eruption," USGS volcanologist Cynthia Gardner said.
Early yesterday, the pace of earthquakes underneath the 8,364-foot volcano more than doubled, to about four a minute, USGS seismologist Seth Moran said. The force of the shaking also rose, with several earthquakes registering between magnitude 2 and 2.8 large enough to be felt by someone standing in the crater.
It's not clear whether the earthquakes are caused by fresh magma moving into the volcano's plumbing, which would significantly raise the odds of a larger, more-destructive eruption.
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.
"We're not seeing evidence of what we would consider to be a significant amount of new magma moving into the system, which lowers the possibility of a large, sustained volcanic explosion," Gardner said.
The current volcanic activity is similar to what occurred in the late 1980s, when earthquakes increased, heralding a series of small eruptions that oozed thick, viscous lava. The lava accumulated to form the 925-foot-high dome in the middle of the crater.
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.
If that's the case, then any eruption probably would be modest, because the old magma has cooled and lost most of the volatile gases that cause fresh magma to be more explosive.
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 firstname.lastname@example.org
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