A recent report from the US Geological Survey (USGS) has disclosed that approximately 400 earthquakes have been documented beneath Mount St Helens since mid-July this year.
This latest sequence of tremors marks the lengthiest since the conclusion of the volcano’s last eruption in 2008. Despite this activity, there are no indications suggesting an imminent eruption.
Providing an update on its website, the USGS noted, “Mount St Helens has had a slight uptick in earthquakes, have you noticed? Most are small (less than M1.0) & not felt at the surface.” The statement reassured that there is currently no cause for concern, as there have been no significant changes in ground deformation or gases, maintaining the volcano at normal (green) background levels.
The USGS also conveyed that since mid-July of this year, the Pacific Northwest Seismic Network (PNSN), responsible for monitoring earthquakes and volcanoes, has located over 400 earthquakes. The most recent weeks have seen approximately 30 located earthquakes per week, a notable increase compared to the average of about 11 earthquakes per month since 2008 at Mount St. Helens.
Reflecting on the historical context, the catastrophic eruption in 1980 claimed the lives of 57 people when Mount St Helens erupted on May 18 in southwest Washington state. Triggered by a 5.1 earthquake, the north flank of the volcano collapsed, resulting in the ejection of over 1,300 feet off the summit and widespread volcanic ash fallout. This event also caused the largest landslide in recorded history.
While the majority of the earthquakes registered since mid-July are of magnitude less than 1.0, as reported by the USGS, Wes Thelen, a volcano seismologist at the agency’s Cascade Volcano Observatory, explained to The Columbian newspaper that such small-magnitude earthquakes detected with sensitive equipment indicate a volcano’s “recharging” process as magma flows through chambers and cracks deep underground.
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