Magma recharging Mount St. Helens, scientists say

SEATTLE – Mount St. Helens is showing signs of long-term uplift and minor earthquake activity, but there are no signs that the volcano in southwest Washington is likely to erupt soon, federal scientists said Wednesday.

The magma reservoir about 5 miles beneath the 8,363-foot volcano has been slowly repressurizing since 2008.

Scientists have suspected that fresh molten rock has been recharging the volcano since the latest eruption, which lasted from 2004 to 2008, but they have only recently been able to confirm it, said Seth Moran, a volcano seismologist with the U.S. Geological Survey.

“This is giving long-term (data) that it’s getting ready to erupt again, but it could be decades before it does something again,” Moran said. “It’s getting ready, but it’s not there.”

The eruption of Mount St. Helens on May 18, 1980, killed 57 people, knocked down a forest, and filled the sky and rivers with volcanic ash.

Moran said the uplift is slow, steady and subtle, measuring about the length of a thumbnail over the past six years. And what scientists are seeing now is similar to activity that occurred in the years after the 1980 eruption, he added.

Scientists with the U.S. Geological Survey’s Cascades Volcano Observatory and the Pacific Northwest Seismic Network have been monitoring subtle changes in the ground and minor earthquakes over the years.

“This is a very tiny signal, and it’s only because we have so many monitors,” said Carolyn Driedger, a spokeswoman with the USGS Cascades Volcano Observatory. Scientists have been able to detect it through a vast network of GPS and seismic monitors, she said.

The agency issued a statement Wednesday in conjunction with a paper that Moran is presenting this week to the Seismological Society of America, she said.

“This is probably what Mount St. Helens does,” Moran said, explaining the volcano recharging. “It may stay perched at ready stage for a long time before it starts to erupt. The reassuring thing is, when it’s really ready to erupt, it gives lots and lots of signs.”