Swarms of quakes in Mount St. Helens crater

The Associated Press

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Qamar said the seismology lab at the University of Washington in Seattle is having trouble keeping up with the hundreds of tiny quakes that began Thursday and show no sign of letting up.

"We're having a swarm of very small quakes — hundreds and hundreds — right under the dome inside the crater," Qamar said.

The swarms of quakes could indicate that a small amount of magma is moving into the mountain's crater, cracking the lava dome, he said.

"It's not a major hazard," Qamar said. But he added: "At this point we want to be cautious. I wouldn't recommend going into the crater today."

Another possibility is that heavy autumn rains have resulted in groundwater percolating into hot regions beneath the volcano, "which would, of course, increase pressures down there," said seismology lab coordinator Bill Steele. It would also raise "the possibility of small steam explosions that could hurl rocks down within the crater itself," he said.

Data from the Cascade Volcano Observatory, including gases collected by aircraft, will help scientists pin down the source of the quake swarm, Steele said. "Changes in the chemical composition can give a clue as to what's happening in the magmatic system below the volcano," he said.

The frequency likely will die down, Steele said.

The quakes are too small to be felt, even close to the southwest Washington mountain, Qamar said.

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.

Mount St. Helens erupted on May 18, 1980, leaving 57 people dead, devastating hundreds of square miles around the peak and spewing ash over much of the Northwest. The last dome-building eruption, in which magma reached the surface and added to the pile of lava on the crater floor, was in October 1986.

Copyright © 2004 The Seattle Times Company

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