Hundreds of earthquakes detected at Mount Rainier on Tuesday. What’s going on?

TACOMA – The swarm began shortly before 1:30 a.m. near Mount Rainier’s summit, with the largest earthquake being a 1.7 magnitude, the USGS said on X just after 9:30 a.m. Tuesday.

“Currently, there is no indication that the level of earthquake activity is cause for concern, and the alert level and color code for Mount Rainier remain at GREEN / NORMAL,” the agency said in a separate statement.

The U.S. Geological Survey Cascades Volcano Observatory and Pacific Northwest Seismic Network have detected the earthquakes at a rate of several per minute and at depths between 1.2 and 3.7 miles below the summit, the USGS said.

No earthquakes have been felt at the surface, according to the agency.

There are typically only about nine earthquakes detected per month at Mount Rainier and swarms usually occur once or twice each year, the USGS said. Even so, swarms are generally much smaller in terms of frequency.

“The last large swarm at Mount Rainier in 2009 had a maximum magnitude of M2.3 and lasted three days. The 2009 swarm had over 1,000 earthquakes, of which the PNSN officially located 120 earthquakes,” the USGS said. “Past swarms have been attributed to circulation of fluids interacting with preexisting faults.”

The agency noted that instruments do not show any detectable ground deformation at the volcano and no anomalous signals have been seen on infrasound monitoring stations.

The CVO and PNSN will continue to monitor the activity and release updates as the situation warrants, according to the USGS.