Maybe Melvin was right??? Quakes at Mount St. Helens prompt warning
Monday, September 27, 2004
By JAKE ELLISON
SEATTLE POST-INTELLIGENCER REPORTER
A surge of strong earthquakes under Mount St. Helens yesterday has seismologists worried that rock and ash could explode from the volcano's dome -- leading scientists to take the rare precaution of issuing a warning for a possible eruption.
Although any eruption is highly unlikely to reach the mammoth proportions of the one in 1980 that killed 57 people, scientists said, the U.S. Geological Survey issued a rare "Notice of Volcanic Unrest."
Officials have since closed several trails on the mountain.
"The main concern is that this increase in activity and the magnitude of the earthquakes we are seeing, we have not seen in a long time, not since the end of the last dome eruption in 1986," said Cynthia Gardner, the acting scientist in charge at the Cascades Volcano Observatory.
Because of the number and strength of the quakes, St. Helens officials have closed the mountain above 4,800 feet, said Peter Frenzen, monument scientist at St. Helens. Portions of the Loowit and Truman trails within the Spirit Lake basin have also been closed for fear that an explosion could trigger landslides.
"It is a new chapter in the volcano's behavior, and that's why we are taking a careful look at it and closing off these areas," Frenzen said.
Swarms of small earthquakes -- of magnitude 1 or less -- pestered St. Helens beginning Thursday, but the number of quakes fell off early Saturday, Gardner said.
Then, late Saturday, the number jumped into the hundreds again, with nearly a dozen temblors hitting magnitudes between 2 and 2.8.
"Here's a signature that was very similar to the signature that we saw back in the days when the dome was building," Gardner said.
Mount St. Helens erupted May 18, 1980, blowing off much of its top in a spectacle that spewed ash and mud for hundreds of miles, downing forests, flooding rivers and killing 57 people.
Experts say the current activity is unlikely to result in an event that large, but even smaller explosions of gas and steam could throw ash thousands of feet into the air and pelt the volcano's rim and sides with rocks. The activity could also cause slides of rocks and mud.
Steam explosions in 1989 and 1991 blew ash as high as 20,000 feet and hurled rocks into the air, Gardner said. "That's our concern."
Similar swarms of earthquakes in 1998 and 2001 were deeper and smaller in magnitude, said Tony Qamar, a Washington state seismologist and University of Washington professor. Those quakes didn't result in explosions.
"One thing that is characterizing this sequence is that the earthquakes seem to have more energy," Qamar said. The quakes may be caused by water seeping down to hot rocks and exploding into steam, or by magma flowing toward the surface, he said.
The current string of quakes could continue for weeks or even months, with the peak swarms occurring over a few days, he said.
"When something like this happens, a lot of people swing into action to try to figure out ways to collect information to find out what's going on," Qamar said.
Gardner said scientists hope to go airborne today to place global positioning equipment on the mountain's dome and flanks. They will use the equipment to measure any changes in the dome's size. The scientists will also be testing the air over St. Helens for gases released when magma nears the surface.
If the seismic activity continues, she said, the possibility grows stronger that explosions from the lava dome will occur.
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