Despite Quakes, Mount St. Helens Isn't About to Erupt
Since mid-March, a succession of small-magnitude earthquakes have occurred beneath Mount St. Helens, the massive volcano in Washington state whose May 18, 1980 eruption killed 57 people. Since that cataclysm was preceded by hundreds of small quakes, the current swarm might seem like a sign that another explosion is impending.
According to the U.S. Geological Survey, though, that's not necessarily the case, and there's no need at the moment to worry.
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Since March 14, there have been 130 quakes reported by the Pacific Northwest Seismic Network, a scientific consortium that tracks such activity. That includes 20 events in the past week, the biggest of which was 1.2 in magnitude.
In a release on its website, USGS explains that the swarms are signs that that that Mount St. Helens is recharging itself, as new magma - semi-molten rock - rises up into the volcano's chamber.
That process puts stress on the crust around and above the chamber, and drives fluids though cracks in the Earth, which in turn causes the quakes.
While that might seem worrisome, recharge events don't necessarily lead to eruptions. "The current pattern of seismicity is similar to swarms seen at Mount St. Helens in 2013 and 2014," USGS explained. "Recharge swarms in the 1990s had much higher earthquake rates and energy release."
As Erik Klemetti, an assistant professor of Geosciences at Denison University, wrote in a Wired.com article, after a big recharge event in 1998-1999, it took five years for Mount St. Helens to experience a series of non-catastrophic eruptions that lasted from 2004 to 2008.
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As USGS and Klemetti noted, there have been no signs so of an imminent eruption, such as changes in gas emissions, shallow quakes, or deformation of the crust around the volcano.
If any of that happens, of course, USGS will pick up on it right away, since Mount St. Helens is equipped with one of the most elaborate volcano monitoring networks on the planet.