Mount St. Helens blows off steam, ash

By Hal Bernton, Nancy Bartley and Ian Ith
Seattle Times staff reporters

TROY WAYRYNEN / AP Mount St. Helens erupted with steam, dust and ash this morning. Mount Rainier is seen in the background.

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"It's a light coating, enough so when you drive it blows up off the highway," said Jeanette Blankenship of the Woodland Motel, 10 miles east of Randle, between the two small towns. "But this is nothing like 1980."

The ash dusting was not enough to effect highway travel or daily life, said Rob Harper, a spokesman for the state Emergency Management agency.

This afternoon, scientists monitoring the volcano said this morning's emissions were extremely minor on a relative scale that rates the explosiveness of volcanic eruptions. On a scale of one to ten, with the blast of May 18, 1980 rating a 5, today's episode was a one, said Jake Lowenstern, a vulcanologist for the US Geological Survey in Vancouver.

Scientists this afternoon reiterated that while they won't rule out a large-scale eruption on the mountain, the most likely scenario is that the volcano will continue as it has for the past week or so: spitting a little ash, a bunch of steam and spectacular sights for weeks or even months as magma works its way to the surface and flows out into the crater to cool.

This afternoon, the USGS said the volcano alert level remains at 3, the highest level, because it is erupting. But they again said they don't think that means major towns or cities are in danger. And they are recalculating whether to keep the alert at that high level.

"We are in an eruptive period, so we don't want people close to the mountain," Lowenstern said.

The alert level means simply that the volcano could erupt, but it doesn't differentiate between small eruptions affecting a small radius and a huge ash plume that would reach cities.

Tests tonight of ash collected from this morning's emissions will help scientists estimate how close the magma is from reaching the surface. But results won't be released until tomorrow.

Meantime, the volcanic gases being released from several fissures in the crater is increasing, but that's a good thing, Lowenstern said: it means the gas is coming out of the magma, reducing the chances of a huge burst of gas when the magma reaches the surface.

The most recent steam and ash plume went up about 9 a.m., puffing as high as 12,000 feet. The emission was not accompanied by strong earthquakes.

Scientists said the steam is probably being generated by a large pool of water that has formed on the southwest side of the lava dome, atop the vents that have opened up in the crater. The water has been bubbling as it boils and volcanic gases such as carbon dioxide and some sulfur dioxide rises through the pool.

The plume contained more ash than previous steam emissions, and rose higher into the atmosphere.

The National Weather Service issued an advisory warning people to "use caution in the vicinity of Mount St. Helens."

The winds pulled the cloud to the north and east, in the vicinity of Spirit Lake. With elk season in full gear, Skamania County Undersheriff Dave Cox said some hunters are in the area and police have contingency plans on the off chance they have to get them out.

Scientists have mounted sensitive equipment in the crater to measure the earth moving and try to figure out how much magma is moving to the surface.

What the scientists do know is that the old lava dome, which built up gradually in a series of small eruptions from 1980-1986 or so, is breaking apart. Analysis of ash scooped up from last Friday's eruption shows it was probably made of pulverized rock from the lava dome.

The south side of the lava dome, near a glacier, has been deformed by the pressure of rising magma, and has risen about 150 feet from its position last month.

Mount St. Helens is a much different mountain than it was in 1980, they stressed. In 1980, the mountain had a full, symmetrical peak. And in the buildup to the May 18 eruption, a bulge slowly built on the side of the peak and then gave way suddenly, causing a massive landslide that suddenly released pressure inside the volcano. That's what resulted in the catastrophic lateral blast that killed 57 people, leveled forests and send a huge column of ash into the stratosphere.

Mount St. Helens now has no bulge other than the lava dome and seems to be venting in a relatively predictable way, Lowenstern said.

"It's very difficult to foresee a situation where we'd have such a rapid pressure release," Lowenstern said.

A steam cloud yesterday went up for about 40 minutes, beginning at 9:42. a.m., and was several times larger than a steam-and-ash eruption Friday.

The steam itself was not alarming to scientists.

But unlike last week's releases, yesterday's venting did not cause even a momentary pause in the earthquakes rocking the area beneath the crater.

"We're not quite sure what to make of that," said Tom Pierson, a USGS scientist who briefed reporters yesterday.

The earthquakes yesterday came virtually nonstop, with small quakes marking time between larger tremors. The earthquakes are believed to be caused by explosive, gas-rich magma struggling to work its way to the surface. Scientists are trying to determine how much fresh magma may be rising so they can get a better handle on the potential size of a future eruption.

But the new quakes, venting and tremors, which first grabbed scientists' attention Sept. 25, are unlike any of the weaker eruptions in the six-year period of activity that followed the 1980 blast.

There is now impressive, visible evidence of the volcano's new power.

The southern portion of a 925-foot lava dome in the crater is now "radically deformed" by the upward pressure of the rising magma, Pierson said.

The deformed area is roughly a quarter-mile long and has been lifted in recent days. In some areas, the uplift ranges from 50 to more than 100 feet, Pierson said.

Scientists are unsure whether a larger area of the lava dome might also be involved in the so-called "uplift." They are hoping a recently installed Global Positioning System (GPS) device on top of the dome will help detect changes.

That would be important information to have, the scientists said. The bigger the uplift, the more explosive the magma that may be working its way up, Pierson said.

"The magma is providing a lot of pressure, and it's pushing real hard," he said.

Though the airspace over Mount St. Helens is now closed to commercial flights, USGS teams continue to drop off crews to work on equipment on the mountain flanks, and to fly over the crater to measure gases.

Another steam cloud puffed up from the volcano around 2:15. p.m. yesterday, just as helicopter crews were peering into a widening vent that is poking through the glacier.

Scientists remain somewhat puzzled about how fresh magma has reached so high in the volcano. They are hoping the addition of more sensitive equipment will give them some clues to its origins.

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com

Copyright © 2004 The Seattle Times Company

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