Researchers are confirming that Mount St. Helens is ‘recharging,’ given the latest data compiled and deciphered.
The volcano originally erupted on May 18, 1980, after just two months of increased seismic activity, and again in 2008 but to a much less extent, ever since the last eruption activity has gradually been growing at the site.
Similar seismic swarms were detected during recharging periods before a small eruption in 2004 and through a period of volcanic activity that ended in 2008. In March through May of this year, swarms of deep earthquakes, not even felt on the surface, have been detected.
However, seismic swarms do not directly indicate that an eruption is imminent, but it could be signs that Mount St. Helens is gearing up for another eruption.
A series of earthquakes caused cracks in the snow and ice at the top of the mountain. On March 27, 1980, ash began to spray from the mountain’s peak.
What happened next caught many scientists by surprise. At 8:32 a.m. on the day of the big eruption, a 5.1 magnitude earthquake shook the area, and the mountain’s summit and much of its northern flank collapsed, sending a huge explosion out from the north side instead of a typical eruption from the top.
Some 3.2 billion tons of ash spewed into the surrounding area, according to the United States Geological Survey. Streets and buildings were covered, and the eruption caused an estimated $1 billion in damage.
Over the nearly four decades since the cataclysmic eruption, the USGS has noticed signs of recovery near Mount St. Helens.
These signs of regrowth are positive, but there are also signs of increased seismic activity under the mountain.
“Mount St. Helens is at normal background levels of activity,” Liz Westby, a geologist with the U.S. Geological Survey–Cascades Volcano Observatory, 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.”
Those quakes originated between sea level and 3 miles below sea level and were too small for people to feel on the surface, even if they had been directly above them, she said.
Even though there has been a swarm of earthquakes, Westby said, that doesn’t necessarily mean that an eruption of Mount St. Helens is coming soon. Volcanic forecasts can be tricky.
“There are several reasons why it is very unlikely that this swarm is a precursor to imminent eruptive activity at Mount St. Helens. 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,” she told ABC News. – Read More