Mount St. Helens has begun rumbling again recently – more than four decades after the worst eruption in US history.
Since February 1, 2024, approximately 350 earthquakes have been recorded at the 8,300-foot Washington state volcano by the Pacific Northwest Seismic Network.
Most of these – more than 95 percent – have been less than magnitude 1.0 and are too small to be felt at the surface.
The largest quake recently felt at the volcano, which is located in southwestern Washington about 50 miles northeast of Portland, Oregon, was a magnitude 2.0 on May 31, 2024.
There are fears the earthquakes could lead to another massive explosion reminiscent of 1980s eruption that left 57 people dead and permanently altered the area’s ecosystem.
In early June, the number of earthquakes recorded per week reached a peak of 38 events per week, mostly happening around 4.6 miles below the crater floor.
Specialized equipment has detected that magma has been flowing through chambers deep underground, causing the volcano to recharge.
‘Short-term increases in earthquake rates are common at Mount St. Helens and are considered part of background seismicity,’ experts at the Cascades Volcano Observatory said in a statement this week.
‘The last two periods of elevated seismicity (in 2023 and 2024) represent the largest short-term increase in earthquake rates since the last eruption ended in 2008.’
However, similar sequences involving even more quakes broke out in 1988 to 1992, 1995 to 1996, and 1997 to 1999. None of these directly triggered an eruption.
The quakes are thought to be caused by pressurization of the magma transport system, which in turn is triggered by the arrival of additional magma, a process called recharge.
Magma gradually bubbles through the lower crust and builds up in a reservoir around 2.5 to six miles below sea level. ‘Recharge’ events break out when magma enters this reservoir, causing quakes.
‘There have been no significant changes in other monitoring parameters (ground deformation, volcanic gas or thermal emissions) and no change in hazards at Mount St. Helens as a result of this activity,’ the Observatory concluded.
However, in 1980, small earthquakes were recorded at the site just before the deadly eruption.
On May 18, 1980, residents flooded the area as they sat in open fields and rooftops as rumors of a volcanic eruption spread. Millions all over the world waited around for two months to see what would happen next.
But on that morning, at 8.32am, the results turned out to be deadly as a magnitude-5 earthquake struck, causing the volcano to lose its crypto-dome and erupt.
Those in the area had nowhere to take cover.
