The earthquakes occurred at depths ranging between 1.2 and 3.7 miles below the surface and have not been felt by residents.
The USGS and the Pacific Northwest Seismic Network (PNSN), which closely monitor the volcano, said such seismic activity is not unusual for Mount Rainier and does not signal an imminent eruption.
What caused the Earthquake swarm?
USGS officials believe the tremors are likely linked to hydrothermal fluids circulating beneath the summit, interacting with pre-existing faults. Similar patterns have been observed in past swarms, and authorities continue to monitor the volcano through seismic, GPS, and infrasound systems.
“Mount Rainier is well monitored,” the USGS noted, with systems in place to track changes using seismic, GPS, infrasound, and webcam data. No other unusual activity has been detected.
The volcano remains at Alert Level GREEN and Color Code NORMAL.
Alert Level GREEN means this is the lowest alert level. It indicates that the volcano is in a normal, non-eruptive state, with no signs of unusual activity or immediate hazards.
Color Code NORMAL is explicitly used for aviation safety. “Normal” means there’s no threat to air traffic from ash clouds or eruptions.
What is an earthquake swarm?
An earthquake swarm is a series of small earthquakes that occur in a short period in a specific area.
They are different from typical aftershock sequences as they don’t follow one main quake. At volcanoes like Mount Rainier, these swarms are often linked to natural processes such as underground fluid movement.
Why does Mount Rainier matter?
Mount Rainier is a stratovolcano located in the Cascade Range. Unlike simpler shield volcanoes, stratovolcanoes are steep, conical mountains formed through multiple eruptions that deposit alternating layers of hardened lava, ash, and volcanic debris (known as tephra). These layers build up over time, giving the volcano its characteristic shape and structure.
Although Mount Rainier hasn’t erupted in over 500 years, it is the second-most seismically active volcano in the northern Cascades. Scientists say its great height, frequent quakes, and glacier coverage make it one of the most potentially hazardous volcanoes in the United States.
Each year, a few hundred small earthquakes are typically recorded in the area. But this swarm is the most active period in over a decade, drawing increased scientific interest.
While the earthquake swarm is the largest in 15 years, current signs suggest it is part of natural volcanic processes.
