posted September 27, 2004 12:31 PM         

By MELANTHIA MITCHELL
SEATTLE - Seismologists believe there's an increased likelihood of a hazardous event at Mount St. Helens due to a strengthening series of earthquakes at the volcano.

"The key issue is a small explosion without warning. That would be the major event that we're worried about right now," said Willie Scott, a geologist with the USGS office in Vancouver.

Initially, hundreds of tiny earthquakes that began Thursday morning had slowly declined through Saturday. By Sunday, however, there had been more than 10 temblors of magnitude 2.0 to 2.8, the most in a 24-hour period since the last dome-building eruption in October 1986, Scott said.

The quakes have occurred at depths less than one mile below the lava dome within the mountain's crater. Some of the earthquakes suggest the involvement of pressurized fluids, such as water or steam, and perhaps magma.

Mount St. Helens is about 55 miles northeast of Portland, Ore.

A group of scientists planned to visit the mountain Monday and conduct a flyover to test for carbon dioxide and sulfur gases, which could suggest the involvement of magma. They'll also erect additional seismic sensors and sophisticated global positioning devices to measure activity.

In the event of an explosion, Scott said the concern would be focused on the area within the crater and the flanks of the volcano. It's possible that a five-mile area primarily north of the volcano could receive flows of mud and rock debris.

That portion of the mountain blew out during the May 18, 1980, eruption that left 57 people dead, devastating hundreds of square miles around the peak and spewing ash over much of the Northwest.

"We haven't had a swarm of earthquakes at Mount St. Helens since 2001," state seismologist Tony Qamar said. "Clearly something new is happening."

Qamar said if an eruption did occur it would possibly involve ash and steam, called phreatic eruptions.

The cause and outcome of the swarm were uncertain Sunday evening.

"There's been no explosions, there's no outward sign that anything is occurring. This is all based on the pattern of earthquake activity that is occurring below the dome," said Scott.

Experts believe there is "an increased probability of explosions from the lava dome if the level of current unrest continues or escalates," USGS and the University of Washington Pacific Northwest Seismograph Network in Seattle said in a joint statement.

A similar swarm of quakes in November 2001 and another in the summer of 1998 did not result in an eruption. However, the quakes could increase the likelihood of small rock slides from the 876-foot-tall lava dome within the mountain's crater.

In the 1986 eruption, magma reached the surface and added to the pile of lava on the crater floor.

posted October 01, 2004 12:32 PM         

A couple days ago there wasn't a cloud in the sky... except for this small cloud over Mt. Hood. It kinda freaked me out. I'm sure it was just a cloud. There's not activity at Mt. Hood... but with what's going on at Mt. St. Helens, I guess people here are just a little on edge.

posted October 01, 2004 01:27 PM         

On 29 September, the US Geological Survey's Cascades Volcano Observatory (CVO) placed Mount St Helens on alert-level two of a three-level system. This signifies that "processes are underway that have significant likelihood of culminating in hazardous volcanic activity".

posted October 05, 2004 01:42 PM         

The mountain is only active in the morning. In the afternoon and evening it's quiet.

Could this have something to do with the moon? ... I mean with gravity and all...

We've been having beautiful weather lately. Sunny and warm... in the afternoon. It's always cold and damp in the early morning (that's just how it is here in September).

I kinda hope it does blow. Everyone is far enough away that no people would get hurt. It would be a beautiful display. You can see it pretty well from the school my kids go to.

A lot of wildlife would die, mostly elk. That would be unfortunate... but a lot of them would probably run away. They seem to know thing.

posted October 14, 2004 10:48 PM         

(10-14) 14:48 PDT SEATTLE (AP) --

More new lava emerged on the crater floor of Mount St. Helens on Thursday, expanding the growing rock formation behind the volcano's old lava dome and emitting a red glow at night.

Airborne observers have seen "vigorous jets" of ash and steam near the new growth, said Tina Neal of the U.S. Geological Survey. Aerial photographs suggest some uplift on the left side of the emerging rock "fin."

Temperatures on parts of the new lobe exceed 1,300 degrees Fahrenheit, and feathery ash blankets red-hot stone.

Dimensions of the new lobe building on the existing lava dome have not been pinned down due to steam and fumes at the site, Neal told a news conference at the Gifford Pinchot National Forest headquarters in Vancouver, Wash., about 50 miles south of the mountain.

"It's grown a little bit since Monday" to about 1,600 feet in diameter and 400 feet high, Neal said. Because the crater floor slopes downward to the north, the new formation on the higher south side is about level with the 1,000-foot top of the old dome.

Seismic activity remained low Thursday, suggesting "an open system" that allows magma to reach the surface without significant obstacles, she said.

This period of dome-building began with intense seismic activity Sept. 23, which indicated magma was breaking through rock as it rose toward the surface. Several steam eruptions followed, and geologists detected lava at the surface late Monday.

The last round of dome-building began in the months after St. Helens' devastating May 1980 eruption and lasted six years.

Gas-rich magma can cause explosive eruptions, but samples taken this week have detected little carbon dioxide or hydrogen sulfide at the site, Neal said. There was no evidence, including increasing earthquakes or ground deformation, to suggest pressure was building, she said.

So far this fall, the most visible bursts at St. Helens have involved steam and small amounts of ash as rainwater and glacier melt combined with hot rock in the crater of the 8,634-foot peak.

As the dome-building continues, it could produce small explosions with little warning, Neal said.

A large explosion is still possible, but is among the least likely scenarios, she said. Such a blast could send a column of steam and gritty ash tens of thousands of feet up and out, posing potential problems for airplanes and road traffic.

Trails within a five-mile radius of the peak remained closed, with the alert level at a mid-range "volcano advisory." The Forest Service, however, reopened some roads and trails near the mountain for hunters and hikers, including the popular Ape Cave and Trail of Two Forests on the mountain's south side.

In its last major eruptive phase before the 1980 blast, the mountain stirred intermittently for 57 years, starting in 1800. Mount St. Helens has been the most active volcano in the lower 48 states and Canada over the past 4,500 years.

St. Helens' 1980 eruption was a lateral blast that hurled debris nearly 20 miles north, killed 57 people and paralyzed much of the Northwest with gritty, machine-clogging ash.

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On the Net:
U.S. Geological Survey regional site: vulcan.wr.usgs.gov/Volcanoes/Cascades/CurrentActivity/

URL: http://sfgate.com/cgi-bin/article.cgi?file=/news/archive/2004/10/14/state1748EDT7956.DTL