VANCOUVER, Wash. — More than 120 tiny earthquakes have taken place during a seven-day period recently beneath Mount St. Helens, but the U.S. Geological Survey said there are no signs of an imminent eruption.
Beginning Nov. 21, the USGS said, four swarms of small quakes were detected. The tiny earthquakes were mostly too small — magnitude 0.3 or less — to be exactly located by the Pacific Northwest Seismic Network or even felt on the surface.
Geologist Liz Westby with the Cascades Volcano Observatory in Vancouver said the earthquakes occurred 1 to 2 miles down. They’re nothing of concern but more than enough to generate excitement for those monitoring the active volcano.
“We’re just simply fascinated by what’s going on because we learn so much more about what’s going on beneath Mount St. Helens and what this all means,” Westby said.
Seismologist Weston Thelen said earthquakes tell scientists the process of magma moving into the volcano is continuing, driving off fluids and gases that fill cracks beneath the surface and inducing the small quakes.
“It is not an indicator of an imminent eruption,” Thelen said. “Just a simple reminder that things are still active down there and that Mount St. Helens will erupt again. It is not imminent.”
Westby said the quakes indicate Mount St. Helens is subtly repressurizing, but little more.
“We’re hearing the heartbeat of Mount St. Helens here through these earthquakes,” she said.
They’d worry if they detected this again, saw abnormal ground uplift or movement and found changes in volcanic gases.
“We would need to see many more signals that would indicate any kind of concern on our part,” she said.
The recent seismic activity alone is simply more data that lends welcome insight into the temperament of a volcano.
Mount St. Helens has proven — even if it was 36 years ago — it’s capable of blowing its top with the best of them.
“The more earthquakes we record,” Thelen said, “the more we understand about the volcano.”