BRANDON HANSEN / KCHW NEWS

Mount Rainier is currently experiencing its largest swarm of earthquakes since scientists began monitoring the Washington state volcano in the 1970s, according to the U.S. Geological Survey (USGS).

The swarm began Tuesday morning and, as of Friday, more than 400 earthquakes had been recorded, with the largest reaching a magnitude of 2.4. The quakes have occurred between 1.5 and 4 miles beneath Rainier’s summit. At its peak, sensors were detecting up to 30 earthquakes per hour. The pace has since slowed, though minor seismic activity continues.

Despite the uptick in tremors, scientists emphasize there is no indication of an impending eruption. Mount Rainier hasn’t erupted in nearly 1,000 years, and USGS monitoring shows no evidence of magma movement or other warning signs such as increasing quake magnitudes, shallow depths, or rockfalls associated with volcanic activity.

Swarm events at Mount Rainier are not unusual. On average, the volcano experiences nine earthquakes a month and one or two swarms each year. However, this week’s activity stands out due to its energy release and number of quakes. For context, the 2009 swarm included 120 located earthquakes over three days, with more than 1,000 events detected in total.

Researchers believe the current swarm is likely the result of hydrothermal fluids—extremely hot water and gases—moving through existing faults deep below the volcano. This process can create numerous small earthquakes, none of which are typically felt by people.

While there’s no immediate threat, the USGS continues to monitor the situation closely. The agency warns that earthquakes at Mount Rainier can still pose risks, such as triggering landslides or lahars—dangerous volcanic mudflows that could affect valleys below the peak.

The USGS added that recent rockfalls on the mountain have been linked to unseasonably warm temperatures, not seismic activity. As of Friday afternoon, the swarm appeared to be tapering off.