Scientists: Small explosion at St. Helens possible within days

MOUNT ST. HELENS, Wash. -- A small explosion of rocks, ash and steam could occur within the next few days within the crater of Mount St. Helens, where earthquake activity has been steadily building for nearly a week, scientists said Tuesday.

"It could certainly happen today; it might not happen for weeks or months," said seismologist Seth Moran of the U.S. Geological Survey's Cascade Volcano Observatory.

Scientists were keeping a close eye on the 925-foot-tall dome of hardened lava that has grown inside the crater since the May 18, 1980, eruption that blew the top off the mountain.

Swarms of tiny earthquakes - more than 1,000 since the mountain began stirring on Thursday - have gradually increased, cranking up to a level not seen since 1986, when the volcano's last dome-building eruption occurred.

Tuesday, the quakes were occurring at a rate of two or three a minute. The volcano was releasing three to four times the energy it was releasing Monday and "yesterday was hopping," said Jeff Wynn, chief scientist at the volcano observatory in Vancouver, Wash., about 50 miles south of the 8,364-foot mountain.

Moran said that in an eruption, rocks two or three feet in diameter could break off from the lava dome and possibly be tossed as far as the rim. But, he and other scientists emphasized, that's not unusual at Mount St. Helens.

Volcanologist Carl Thornber said scientists are baffled by the activity, unusual because the earthquakes are so shallow.

"Everything right now is within the dome or within a kilometer," Thornber said at the Johnston Ridge Observatory at the base of the mountain, where surrounding hillsides are still covered with trees toppled by the 1980 blast.

Largely unheralded steam explosions in 1989, 1990 and 1991 all broke pieces of lava off the dome, Moran said.

The likelihood of a significant eruption "is fairly small," Moran said. "There's a range of possibilities still for where this may go. It might go away and nothing happens. That becomes less likely as this continues to increase. At the other end, we could have a reactivation of the lava dome-building sequences."

Scientists are "not sure where this is going and it's really hard to communicate this succinctly," he said.

Seismologist George Thomas at the University of Washington said that on a scale of zero to 10, with 10 being the explosion at the mountain in 1980, the current activity would rate a one. Thomas said any rocks, ash or steam coming out of the volcano would most likely be contained within the crater itself.

"The alerts we're sending out are just to protect hikers and scientists doing research within the crater," he said.

Scientists are trying to determine if the quakes are caused by steam resulting from water seeping into the dome or more seriously, by magma moving beneath the crater.

Early tests of gas samples collected above the volcano by helicopter Monday did not show unusually high levels of carbon dioxide or sulfur.

"This tells us that we are probably not yet seeing magma moving up in the system," Wynn said.

Scientists were setting up new Global Positioning Satellite stations all over the mountain to track its movement, adding about six to the dozen or so already in place. Using GPS data, scientists can detect tiny movements by the Earth.

Observatory scientists are working 12-hour days, Wynn said. "This is just a hoot to them. This is what they live and breathe and now it's walking and talking to them."

The USGS issued a notice of volcanic unrest on Sunday, citing "increased likelihood of a hazardous event." U.S. Forest Service officials closed hiking trails above the tree line at 4,800 feet. The visitors center and most other trails at the Mount St. Helens National Monument remained open.

Mount St. Helens roared to life in 1980, when the massive explosion and landslide obliterated the top 1,300 feet of the volcano. The blast and subsequent mudflows killed 57 people, leveled hundreds of square miles of forests, spewed mud and debris for miles and spread volcanic ash across much of the Northwest.

In October 1980, five months after the volcano's devastating eruption, the lava dome began building in the crater. The last dome-building eruption came six years later, though steam explosions have periodically rocked the dome.

Federal scientists raised the volcano warning at Mount St. Helens to the equivalent of an orange alert this morning, as earthquake intensity increased and preliminary measurements showed magma may be moving into the crater.

Volcanic explosions could occur at any time, and an eruption that spews rock and ash up to three miles from the crater is possible, said Cynthia Gardner, of the U.S. Geological Survey's Cascades Volcano Observatory. A larger eruption is also possible, but not likely, scientists said.

Because the area around the volcano is uninhabited, the risk to human life and property is low, said USGS geologist Dan Miller.

"I can't imagine a small to moderate eruption having an impact on people or property," Miller said at a briefing this morning.

Monitor the volcano

The Mount St. Helens live Web camera is back in action after more than a year's down time because of technical glitches. Pictures are taken from the Johnston Ridge Observatory five miles from the crater and updated every five minutes. The site is: www.fs.fed.us/gpnf/volcanocams/msh/

It's also possible the volcanic activity will die out, Gardner added.

"At this point, we're saying there's a heightened possibility of an eruption," she said. "We're not guaranteeing you an eruption."

Overnight, the pace of earthquakes beneath the volcano more than doubled, to about four a minute, said USGS seismologist Seth Moran. The size of the shaking also intensified, with several quakes registering at magnitude 2 to 2.5 - strong enough to be felt by somebody who was standing in the crater. Previously, most of the earthquakes ranged from magnitude 1 to 1.5.

A monitor installed Monday on the small dome inside the volcano's crater also detected about two inches of upward bulging over the past 12 hours.

That means magma is almost certainly moving into the dome, making an eruption more likely.

Seismograph printouts at the University of Washington show how much things have changed at Mount St. Helens in the space of a few days.

Early last week, the pages were blank, except for an occasional, tiny blip. Yesterday, they were almost solid black, each dark scrawl representing another small earthquake from beneath the volcano.

HARLEY SOLTES / THE SEATTLE TIMES
University of Washington seismographs show almost continuous swarms of earthquakes shaking Mount St. Helens yesterday. Steve Malone, a research professor in Earth and space sciences, studies the readings. At the upper right, almost black, is the current graph for Mount St. Helens; below it, showing no activity, is the one for Mount Rainier.

"It's continuous," said UW seismologist Steve Malone. "We know there's a lot of rock breaking, and sooner or later something's got to give."

When it does, the result could be small explosions or eruptions, possibly accompanied by an outpouring of lava onto the 925-foot dome that has built up in the crater since the volcano's massive eruption in 1980, scientists say.

But the fact that volcanic gases are not escaping from the mountain in high levels means that fresh magma has not been welling up from deep underground, said Willie Scott, a volcanologist at the volcano observatory. And in the absence of new magma, any eruption will not be major.

"That makes us think we're not in a situation where, imminently, we could have a large, sustained, explosive eruption," Scott said.

Field crews spent the day yesterday placing instruments around the volcano to measure any bulging that would be expected if magma does begin to move upward. Some of the instruments will deliver continuous, real-time data from fixed stations, while others will be moved around from place to place, to collect information over as many points as possible, Scott said.

As recently as last month, instruments already deployed around the volcano showed no evidence of any bulging, Scott said. In the two months before the May 18, 1980, eruption, the mountain's northern flank bulged outward more than 200 feet.

Convinced the volcano was already going off yesterday, many people around the region called the volcano observatory to report what they thought were eruption plumes. What they really saw were wisps of clouds or dust from rockfalls in the crater, Scott said.

HARLEY SOLTES / THE SEATTLE TIMES
In the top graph, University of Washington seismographs show swarms of earthquakes shaking Mount St. Helens. The chart below it graphs the quieter readings from Mt. Rainier.

State and regional emergency planners participated in a conference call with scientists yesterday to get an update on the volcano's status and review the emergency-response plan written after the 1980 eruption killed 57 people, destroyed 200 homes and unleashed the biggest landslide in recorded history.

Although the plan has been updated in recent years, some of those on the conference call couldn't remember where their copies were, Malone said.

"It's been awhile," he laughed.

Scientists say any hazards from a small explosion, eruption or mudflow would be confined to the mountain's unpopulated flanks.

However, it's likely the mountain also will throw up an ash plume, which could kill the engines of any aircraft flying in the area, Scott said. If a plume occurs, the volcano observatory would notify the National Oceanic and Atmospheric Administration and the Federal Aviation Administration, which would reroute air traffic away from the drifting plume.

Mount St. Helens has rumbled several times since 1980, with thick, pasty magma pouring out and creating the lava dome that now sits inside the lopsided crater. The last lava outpouring was in 1986.

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