Magma beneath Mount St. Helens is ‘recharging,’ scientists say

VANCOUVER, Wash. (KPTV/Gray News) - Mount St. Helens, which notoriously erupted in 1980, has been showing signs of increased seismic activity lately, according to the U.S. Geological Survey. It’s thought to be part of the volcano’s natural magma recharging process.

The volcano, which sits on the Pacific “Ring of Fire,” has experienced around 350 earthquakes since the beginning of February, with 38 alone in the first week of June.

Most of these earthquakes were not noticeable, but one registered 2.0 magnitude on May 31 — strong enough that it could have been felt by humans.

More than 95% of the earthquakes have been less than magnitude 1.0 and are too small to be felt at the surface.

Although earthquakes under Mount St. Helens are not uncommon, the recent seismic activity is the largest short-term increase in earthquakes since the volcano last erupted in 2008.

However, there have been other periods on similar seismic activity that did not lead to eruptions, namely in 1988-1992, 1995-1996 and 1997-1999. So more earthquakes does not guarantee an eruption, the USGS’ Cascades Volcano Observatory in Vancouver, Washington, said.

Small earthquakes beneath Mount St. Helens are generally thought by scientists to be part of a recharge process where magma builds up beneath the volcano.

“Magma slowly rises through the lower crust and accumulates in a reservoir about 2.5 to 6 miles (4‒10 km) below sea level,” the USGS said. “Recharge events can occur when magma enters this upper reservoir and increases stresses that lead to earthquakes.”

The USGS reported that there have been no other signs of coming eruption, such as ground deformation, volcanic gas or thermal emission.

“High rates of seismicity, interpreted as recharge, have been observed in the past at Mount St. Helens and at other volcanoes and can continue for many years without an eruption,” the observatory wrote. “No significant changes have been observed in other monitoring parameters and there is no change in alert levels at this time. Mount St. Helens remains at normal, background levels of activity.”

The infamous major eruption on May 18, 1980, killed 57 people and radically changed the landscape of the area.

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