Swarm of quakes shake Mount Saint Helens crater

05:12 PM PDT on Friday, September 24, 2004

From KING5.com and Wire Reports

USGS The deep crater of Mount St. Helens.

SEATTLE – The experts monitoring Mount Saint Helens say the swarms of small earthquakes in the crater of the volcano could be caused by steam explosions.

A statement from the U.S. Geological Survey at Vancouver and the University of Washington seismology network in Seattle said rain flowing down to the hot rocks can result in explosions that hurl rocks hundreds of yards.

"There are still warm spots within the dome or crater fill," Seth Wren, U.S. Geological Survey, told KING 5. "As that continues to cool and cracks open up, some of this water could be getting into these warm areas and causing pops and burst."

But those pops and burps can throw boulders hundreds of yards if that steam blows out.

Scientists are focusing their attention on the mountains dome, the part of the mountain that's been growing back, since the 1980 eruption.

“We don't think this means there's another eruption any time soon,” said Steve Malone, a University of Washington seismologist. “We don't think new rock or magma is moving into the volcano…This is a readjustment within the local plumbing system.”

Scientists believe what is moving around, is that rainwater has moved down through new cracks formed in the dome, exposing the water to heat further down, that the rock is cracking, and the water is turning to steam.

Time lapsed pictures taken during the dome's formation between 1980 and 1986 are providing a sense of that.

Since May 18, 1980, when Mt. St. Helens erupted with incredible force, killing 57 people, the mountain has become active several times. The last time magma, liquid rock, was on the move was 1998.

“Our best guess is that nothing will happen,” said Malone. “But there is a chance that a steam explosion could occur. But a major eruption…is very unlikely.

The statement said there was no evidence of a new intrusion of magma. But geologists also say that could explain the quakes. They add it’s unlikely there is any hazard to anyone outside the crater.

The last similar swarm of small quakes at the volcano was in November 2001. The last time magma moved into the crater was 1998.

Another quake in Olympic Peninsula

Meantime residents near Port Angeles, Wash., felt some shaking Friday morning as well.

A magnitude 2.8 earthquake hit 18 miles east of Port Angeles, Wash., at about 10 minutes after midnight. The depth of the earthquake was measured at 6 miles, according to the Pacific Northwest Seismograph Network.

There were no reports of damage or injuries.

The Associated Press contributed to this report.