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What is an earthquake swarm? Washington's most famous volcano records its ‘largest’ one in 15 years
Mount Rainier's seismic activity has surged, with the USGS noting the largest earthquake swarm since 2009.
One of the most famous mountains in Washington, Mount Rainier, has been rumbling over the last day due to the amplified seismic activity.
The United States Geological Survey (USGS) issued a report early on the morning of 8 July, with scientists registering the “largest” earthquake swarm at the volcano since 2009, which started at 1.29 AM PT. The data, shared in an X post (formerly Twitter), showed “hundreds” of small earthquakes had been detected by 9 AM, with the strongest registering a magnitude of 1.7.
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Experts say there’s no reason to panic just yet
The Pacific Northwest Seismic Network (PNSN), which monitors volcanic and earthquake activity in the region, reassured the public that there’s “no indication that the level of activity is cause for concern, alert level and color code for Mount Rainier remain at GREEN/NORMAL.”
The USGS explained that while an exact cause hasn’t been pinpointed, similar swarms in the past have been linked to “circulation of hydrothermal fluids beneath the summit interacting with preexisting faults.”
“Mount Rainier is well monitored by a dense network of seismic, infrasound, GPS, and webcam stations,” the USGS said, adding that “no other changes are apparent at the volcano at this time.”
Notably, Mount Rainier is the second-most seismically active volcano in the northern Cascade Range and is considered “potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle.”
Though Mount Rainier hasn’t had a “significant eruption” in over 500 years, scientists typically detect a “few hundred” small earthquakes each year at or near the volcano.
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So what exactly is an earthquake swarm?
These are sequences of small quakes that occur in a specific area over a short period of time. Most of the time, they’re nothing to worry about. As PNSN explains, “Volcanic-tectonic earthquakes (VTs) are, simply put, caused by slip on a fault near a volcano.” These often occur where the Earth's crust is already weak.
