VANCOUVER, Wash. - Volcano experts are trying to figure out what other tricks Mount St. Helens might show off after Friday's eruption, the first in 18 years at the region's most active volcano.
"Is this it, or is Mount St. Helens going to do more?" said Jon Major, a U.S. Geological Survey hydrologist who posed the question soon after the mountain produced a small eruption, the kind his fellow scientists had predicted earlier this week.
Later Friday, USGS and University of Washington scientists put out a update stating, "Additional steam and ash eruptions similar to today's could occur at any time."
They also noted that the earthquake pattern at the volcano was increasing, with one or two occurring each minute. The largest post-eruption quake was rated magnitude 3.
"At this point, we are still trying to interpret what this means," Major said. "These could be like aftershocks to an earthquake."
An alert about the volcano's potentially dangerous behavior remained in place, in part because of continued uncertainty about it.
"This is perhaps the opening salvo," Major said of Friday' eruption. "We might see a few more like this."
Later, he and other scientists said they can't pinpoint what will happen.
Major cited these among the possible scenarios:
* Another similar, small-scale eruption.
* A dome-building eruption of lava on the volcano's surface.
* Increased glacial melting, without flood risk.
Friday's midday spurt of steam and ash sent a cloud 16,000 feet into the air. The eruption, which lasted 24 minutes, began at 11:57 a.m. It hurled rocks as big as 2 feet in diameter around the crater but no farther.
The stones destroyed a seismometer and a global positioning satellite device on the lava dome, but USGS crews on the flanks of the mountain were unhurt.
A light dusting of ash drifted southwest, some of it landing on cars in the parking lot of the Cascade Volcano Observatory, the suburban Vancouver office building where Major and about 55 other USGS scientists work.
Though the observatory is about 50 miles from the mountain, some scientists caught a glimpse of the ash plume before it dissipated.
"This is Mount St. Helens saying, 'I'm still an active volcano; don't write me off,'" Major said.
Volcano experts remain uncertain about what might have caused the volcano to reawaken after so many years of relative quiet.
"We don't exactly know what triggered today," Major said.
He and others speculated that the steam might have shot out of the mountain after groundwater came in contact with hot rocks underground.
"Now the cork has popped," said Jeff Wynn, a geophysicist who is chief of the USGS volcanic hazards programs. "Likely what we are seeing here is a brief relief of the pressure."
Major and others said they were glad the volcano performed as they forecast, especially because the blast did not hurt anyone or cause damage outside the volcano's crater.
"It's hard to imagine the incredible violence of a volcano until you see solid rock pulverized and thrown thousands of meters, and that's what happened here," Wynn said.
"There's a great sense of relief at this point," Major said. "We anticipated this. We weren't wrong."
Friday's eruption was minor in comparison with the cataclysmic blast of May 18, 1980, that blew off the mountain's top, obliterated the surrounding landscape and killed 57 people. In size and intensity, the two were as different as a pea and a basketball, Major said.
But many explosions similar to Friday's occurred after the big eruption in 1980, when the mountain built the lava dome at the center of its crater. Between 1980 and 1986, hundreds of small bursts of steam and gas took place.
Scientists issued a level 2 alert Wednesday, three days after a previous advisory that had prompted the U.S. Forest Service to cancel permits to climb the 8,383-foot peak and close several trails.
Now, it's too dangerous inside the volcano's crater for scientists to enter. Instruments destroyed Friday won't be replaced unless the mountain quiets down for several days, Major said.
Later Friday, the intense shaking that preceded the eruption subsided for several hours. But about 4 p.m., earthquake activity resumed.
Scientists continue to wonder whether magma beneath the lava dome might force its way toward the surface.
"Something drove this thing to spurt," Wynn said.
At this point, the evidence is contradictory.
"We're not seeing any significant seismic evidence of anything working its way up at depth," he said.
All of the recent earthquakes have emanated from relatively shallow points beneath a volcanic system that might reach down as far as 50 or 100 miles beneath the earth's surface, Wynn said.
Friday's explosion tore a 100-foot hole or vent in the volcano's crater.
Scientists who flew near in the area in helicopter about the time of the eruption said the hole appeared to drop down about 100 feet, then angle south under glacial ice. The opening is near the southern edge of the lava dome, in a spot where scientists previously noticed cracks in the ice.
After the eruption, runoff from the crater increased but did not create a flow of debris and did not threaten to flood the Toutle River valley, Major said.
The eruption took place as teams of scientists stepped up efforts to assess the mountain's behavior. They placed additional sets of seismometers around the mountain, used a remote thermal detection device to check for unusual heat - there was none - and tested the air for volcanic gases (also negative).
After the eruption, they also gathered samples of ash for analysis.
Scientists have found no evidence of magma or molten rock breaking through the volcano's surface.
Susan Gordon: 253-597-8756
Originally published on October 2, 2004.