Mount St. Helens sends steam and ash thousands of feet into the air...
COLDWATER RIDGE VISITOR CENTER — Mount St. Helens yesterday again threw up billowing, anvil-shaped clouds of steam and a little ash, the largest explosion yet since it stirred back to life late last month. But the event didn't ease the pressure building up inside the volcano, and scientists cautioned that this was just an unsuccessful throat-clearing before what is expected to be a bigger eruption in the days or weeks ahead.
"We could have a much larger event, essentially at any moment," said Willie Scott, the chief scientist for the U.S. Geological Survey.
The first 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.
"What happened today wasn't a very big deal," said Jake Lowenstern, a USGS geologist in Vancouver, "though it was nice to look at."
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.
Scientists have repeatedly said they don't expect anything like the May 18, 1980, blast that ripped off the top of the mountain and unleashed a sideways explosion that killed 57 people.
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.
Lava dome "deformed"
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. And a portion of a nearby glacier is deeply cracked.
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. JAMES BRANAMAN / THE SEATTLE TIMES "Oh my God! I can't believe it," Theresa Graham of Portland repeats yesterday between snapping photographs of the volcano spewing steam and ash. A pool of water inside a widening vent is probably contributing to the steam eruptions, scientists 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.
Work continues on flanks
The 1980 blast ranked a 5 on the scale scientists use to rate volcano eruptions. In recent days, scientists have guessed that a new eruption could rate a 2 or 3. But they said yesterday they could re-evaluate their forecasts based on new measurements.
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. They reported that a pool of water had formed inside the vent.
That water is probably what is boiling off to make the steam clouds, the scientists said. As more fresh, hot gas gets closer to the surface, bigger steam releases could occur in coming days.
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.
Ash-cloud warning
Meanwhile, yesterday, officials in counties immediately around the volcano were stepping up preparations for the possibility of ash clouds.
A cold front moving into the area today will mean that if ash is spewed into the atmosphere, it will drift southwest, toward communities such as Castle Rock, Kelso and possibly Portland. Still, scientists have downplayed the potential for ash clouds, saying inhabited areas would probably get a light dusting at most.
The ash, which would largely be dust but with about 4 percent silicate, has not been shown to pose long-term health effects, said Dr. Justin Denny, the public health officer for Clark and Skamania counties.
The biggest short-term risk is to people who suffer from asthma or chronic lung diseases; they should stay indoors and avoid exposure as much as possible, Denny said.
For those who need to go outside during a big ash fall, Denny recommended surgical masks that cover the mouth and nose, and possibly goggles to protect the eyes.
Hal Bernton: 206-464-2581 or hbernton@seattletimes.com
