Mount St. Helens' magmatic system could be "recharging," resulting in a swarm of "deeply originated" earthquakes that have been detected since March, ABC News reported.
Mount St. Helens' eruption 37 years ago on May 18, 1980, stunned scientists and residents, as they saw the scenic mountain blow open into a small crater reawaking the volcano and triggering a huge landslide after a series of earthquakes, The Oregonian reported.
The surprise eruption led to 57 deaths with destruction covering 230 square miles. The following mudflows destroyed 27 bridges and 200 homes, The Oregonian noted.
ABC News wrote that seismic swarms similar to the current activity happened during recharging periods from 1986 to 2004, when a small eruption happened. Seismic activity clusters had resumed before Mount St. Helens' most recent eruption in 2008.
Liz Westby, a geologist with the U.S. Geological Survey–Cascades Volcano Observatory, told ABC News that re-growth around Mount St. Helens was a positive sign of stability. She also took notice of the increased seismic activity.
"Mount St. Helens is at normal background levels of activity," Westby told ABC News. "But a bit out of the ordinary are several small magnitude earthquake swarms in March to May 2016, November 2016 and April 16 to May 5, 2017. During the April 16 to May 5, 2017, swarm, we detected well over 100 earthquakes, all below a magnitude 1.3."
Westby added, though, that just because earthquake activity has returned, it does not mean that Mount St. Helens is about to erupt again, ABC News noted.
"There are several reasons why it is very unlikely that this swarm is a precursor to imminent eruptive activity at Mount St. Helens," Westby told ABC News. "It is similar to ones in the past that did not lead to surface activity. It consists of very small earthquakes occurring at relatively low rates. There are no other geophysical indicators (like surface deformation, tilting, increased volcanic gas emissions) of unrest."
Erik Klemetti, an assistant professor of geosciences at Denison University, wrote in an article for Wired magazine last year that while there are no changes in gas emissions or deformations that would indicated an eruption on Mount St. Helens soon, the magma that will make up its next eruption is probably creeping to the surface.
"It might take a big recharge event to really get the system primed for the next eruption," Klemetti wrote for Wired. "This question — what might ultimately trigger that next eruption — is one of the big ones in volcanology. However, what we can say is that no volcano is truly 'dormant' when it's not erupting. It's just that most of the action is happening far beneath our feet."
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