From: Reed Stevenson, Reuters
Published September 28, 2004 12:00 AM

Rumbling at Mount St. Helens Triggers Alert

SEATTLE — Government scientists have warned hikers and researchers not to go near the crater of the Mount St. Helens volcano because there is an "increased likelihood" an explosion could occur, sending rocks and debris down the side of the mountain.

A swarm of shallow earthquakes have rattled the lava dome that formed in the crater after the mountain's violent 1980 eruption, which spewed mud, rocks and ash and flattened acres of evergreen spruce forest.

"Seismic activity at Mount St. Helens has changed significantly during the past 24 hours and the changes make us believe that there is an increased likelihood of a hazardous event," the U.S. Geological Survey said in a statement issued on Sunday.

Smaller earthquakes, most likely caused by hot rock coming into contact with underground water, may have triggered more significant seismic activity involving magma, Steve Malone, director of the University of Washington's seismology lab, said on Monday.

"Our interpretation is that this activity now involves the magmatic (molten rock) system," Malone said. "Whatever has gone on has impacted the magmatic system."


Since late last week, about 10 earthquakes of magnitude 2 to 2.8 occurred less than a mile below the lava dome's surface, which the seismologists said "point toward an increased probability of explosions from the lava dome if the level of current unrest continues or escalates."

A small-scale explosion of the lava dome would most likely spew rocks and muddy debris to the rims of the volcano's crater and down the sides of the mountain, Malone said. The violent eruption two decades ago changed the shape of the entire area.

The U.S. Geological Survey in Vancouver, Washington, near Mount St. Helens, said it would conduct tests to see if the smaller earthquakes triggered any magma activity.

The last time strong earthquakes were detected was in 1989, when fresh magma entered the volcano's lava system.

Trails around the volcano, which is a national monument, are a popular destination for hikers.


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