Hundreds of earthquakes detected at Mount Rainier on Tuesday. What’s going on?
AI-generated summary reviewed by our newsroom.
- Mount Rainier experienced its largest earthquake swarm since 2009 on Tuesday.
- USGS reported hundreds of small quakes under the surface near the stratovolcano's summit .
- The agency said there was no cause for concern but they were monitoring the activity.
Hundreds of small earthquakes were detected at Mount Rainier on Tuesday in the largest such swarm at the active stratovolcano since 2009, according to the U.S. Geological Survey.
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 in the morning.
The U.S. Geological Survey Cascades Volcano Observatory and Pacific Northwest Seismic Network detected the earthquakes at a rate up to several per minute and at depths between 1.2 and 3.7 miles below the summit, the USGS said.
No earthquakes were felt at the surface, according to the agency’s morning brief on the swarm.
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 did not show any detectable ground deformation at the volcano and no anomalous signals were seen on infrasound monitoring stations.
The CVO and PNSN continued to monitor the activity Tuesday and the USGS said it would provide new information as the situation warranted.
No updates were released as of late Tuesday afternoon. Efforts to reach the USGS to discuss the earthquakes were unsuccessful.
This story was originally published July 8, 2025 at 11:14 AM.
