Thursday, September 30, 2004
TOM VOGT and ERIK ROBINSON Columbian staff writers

With chances of a small to moderate eruption increasing, scientists on Wednesday raised the advisory at Mount St. Helens to the second-highest of three alert stages.

    Even so, Forest Service managers decided not to scale back public access to the flanks of the volatile Cascade peak. Cliff Ligons, manager of the Mount St. Helens National Volcanic Monument, also opted to leave the popular Johnston Ridge Observatory open after consulting with U.S. Geological Survey scientists.

    "The mountain can change its mind any time it gets ready," Ligons said.

    New seismic information indicates that the likelihood of an eruption is significantly greater than it was 24 hours earlier, geologist Cynthia Gardner said Wednesday afternoon at the Cascades Volcano Observatory in Vancouver. But any eruption would probably be a small to moderate event, said Gardner, acting scientist in charge of the USGS center for volcanic research.

    That could mean a burst of molten rock out of the mountain's 876-foot-tall lava dome, which oozed up from the crater floor in a series of magma extrusions between 1980 and 1986. Or, it could mean a more explosive outburst that could pepper areas up to three miles away with rock fragments and ash. At the three-mile range, the fragments probably would be less than an inch in size, she said.

    The closest building to the crater is the Johnston Ridge Observatory, five miles to the north.

    Scientists said earthquake measurements show increased activity, but another key indicator, analysis of gases in the crater, does not signal that a major eruption is likely.

    USGS scientists Mike Doukas and Steve Schilling stepped off a helicopter Wednesday afternoon at Hoffstadt Bluffs with news of a fruitless search for the telltale gases that would indicate molten rock was surging toward the surface.

    "Fresh magma would be accompanied by a big increase in carbon dioxide gas, fumaroles, or venting," Doukas said. "None of that is happening."

    Scientists will continue to monitor gas levels daily or every other day, Gardner said.

    3.0 on the Richter

    The rate of earthquakes under the volcano's dome increased to about four a minute by Wednesday afternoon double the rate earlier in the week. The magnitude level topped out at 3.0 on the Richter scale Wednesday afternoon, after a flurry of 1.0 and 1.5 shakes earlier in the week.

    Despite the underground activity, all appeared calm on the mountain Wednesday afternoon during a helicopter flyover. Clouds hugged the mountain's flanks, but above the clouds the crater glittered in bright sunlight. Only a few puffs of steam issued from vents in its craggy dome.

    The mountain's resident elk herd grazed peacefully at an elevation of 4,000 feet on Studebaker Ridge. Alders and willows in fall foliage of red and orange broke the monotony of the gray-brown landscape.

    Though no changes in the mountain were visible from above, scientists said they had never seen this pattern of behavior at Mount St. Helens. Past swarms of earthquakes have either dissipated or eventually released the pressure with a steam or gas eruption, said Bill Steele, seismology lab coordinator at the University of Washington.

    "Some very bright people are throwing out some very interesting concepts and ideas," said Carl Thornber, a USGS geologist.

    Magma seems to be playing a role in the seismic activity, said USGS seismologist Seth Moran. The subterranean molten rock apparently has been working its way to the surface for quite awhile and may have hit a roadblock about 2 kilometers below the dome.

    It's probably not a big lake of magma: more like a narrow spigot, Moran said. The plug near the top of the conduit probably is a remnant of an earlier eruption, a portion of magma that never made it out of the fissure and then cooled and solidified.

    Weighing theories

    When the earthquake swarm started Sept. 22, scientists theorized that cool water from recent heavy rains had trickled below the dome, fracturing the hot rock formations and generating the earthquakes.

    But the quakes have gone on too long to support that theory, Gardner said.

    "If it was simply groundwater, the quakes would have died off," Gardner said. "We're looking at a ramp-up of magnitude and of number."

    Such an energy release has to involve magma, which breaks rock as it makes its way to the surface, scientists say. But it's not a fresh magma flow, according to scientists who have been measuring gases over the crater.

    As the molten rock bubbles up from the earth's interior, it releases carbon dioxide and hydrogen sulfide.

    When Doukas and Schilling relayed they had discovered negligible levels of carbon dioxide during their second helicopter flight in three days, scientists in Vancouver focused on a new theory.

    "So, it seems that we are not seeing hot, fresh, volatile magma sitting at shallow levels," Gardner said.

    Just like a soft drink, magma gets "flat" the longer it sits around, losing the "carbonation" that helps power an eruption.

    Gardner said scientists also have been tracking surface movement inside the crater. They placed a Global Positioning System locator earlier this week on a lobe of the dome; the sensor showed a northward drift of 4 centimeters about 1.5 inches over the span of about 12 hours.

    That discovery yielded yet another line of thinking: that a newly formed glacier along the south wall of the crater is shoving the lava dome northward. The glacier is now at least as large as the lava dome itself, Schilling said, comprised of an estimated 120 million cubic yards of ice, snow and earth.

    The side of the mountain was bulging at the rate of 5 feet a day just before the catastrophic eruption of May 18, 1980. When the north flank gave way, in the biggest landslide in recorded history, it uncorked a blast that killed 57 people, leveled 150 square miles of alpine forests and decapitated the top 1,300 feet of mountain.

    Drawing a crowd

    Meanwhile, tourists and news reporters flocked to Mount St. Helens on Wednesday for a first-hand view of the renewed excitement. At least two hikers, Brian Phillips of Aloha, Ore., and Hugh O'Reilly of Portland, decided against a planned overnight hike from Johnston Ridge to the Mount Margaret backcountry nine miles to the north.

    "Brian and I have climbed a lot of mountains, and it's not going away," he said, standing near the volcano's gaping crater. "Although, that's not the case here."

    Fascinated scientists, agency officials and tourists all stood together at Johnston Ridge watching for what happens next.

    "It's the only active volcano in America that behaves this way," Ligons said. "The exciting thing to me is we're going to learn more. It's alive."

    Columbian staff writer Kathie Durbin contributed to this story.

    Update

    Previously: On Sunday, the U.S. Geological Survey issued a notice of volcanic unrest, the first of three alert levels, at Mount St. Helens.

    What's new: With accelerated seismic activity, the USGS raised the alert level Wednesday morning to a volcano advisory, the second of three levels. But there are no signs indicating new magma that could generate a large sustained eruption.

    What's next: Scientists will continue to monitor several indicators, including earthquakes, level of magma-related gases and deformations of the dome and crater.

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