Mount Rainier, the iconic snow-covered peak in Washington state, has recently been experiencing a notable increase in underground activity. Since the early morning hours of July 8, 2025, the volcano has been shaking with a series of small earthquakes, known as an “earthquake swarm,” marking the most significant seismic event since 2009. Scientists have been diligently tracking and pinpointing each tremor, occurring at depths between 1 and 4 miles beneath the summit, a common occurrence for volcanic activity of this nature. The largest recorded tremor measured 1.6 on the magnitude scale.
While earthquake swarms are not uncommon for Mount Rainier, with an average of about 9 earthquakes per month and occasional smaller swarms occurring 1-2 times per year, the current swarm stands out due to its size – with hundreds of earthquakes in a single day. However, this level of activity falls within the range of normal volcanic behavior. The last significant swarm in 2009 lasted three days and included over 1,000 earthquakes, with the largest reaching a magnitude of 2.3. Similarly to the current swarm, it was attributed to fluid circulation and did not pose any threat to public safety, with the mountain returning to its usual state of calm following the event.
For visitors to Mount Rainier National Park, the ongoing earthquakes do not present any immediate danger, as they are too minor to trigger rockfalls or impact the glaciers. It is noteworthy that recent warm weather has caused more noticeable rock and ice falls than the earthquake swarm itself.
The seismic activity at Mount Rainier is attributed to the movement of hot water and steam through the underground fissures and faults in the rock, similar to a large plumbing system. Scientists believe that the current swarm is primarily caused by heated water from the volcanic system circulating through existing fractures in the Earth’s crust, creating slight vibrations as it moves through the rocky channels. These tremors are of minimal intensity, with the largest registering only 1.6 on the magnitude scale, too weak to be felt by humans.
Researchers are closely monitoring various indicators to ensure the stability of the situation, including earthquake activity, ground deformation, infrasound, and webcam imagery. As of now, seismic activity is the only parameter showing deviations from the norm. Scientists would be concerned if earthquakes started occurring at shallower depths, changed characteristics, or if the swarm persisted significantly beyond a week. Different seismic signals, such as “hybrid” or “low frequency” earthquakes, could also raise concerns and prompt further investigation.
The current alert level for Mt. Rainier remains at GREEN/NORMAL, indicating no immediate threat of volcanic activity despite recent seismic activity. While the ongoing swarm of earthquakes serves as a reminder of the volcano’s active nature, there are currently no signs pointing to an imminent eruption. Unlike alarm clocks, volcanoes do not follow predictable schedules, with Mt. Rainier’s last eruption occurring approximately 1,000 years ago. As scientists monitor this geological phenomenon closely, we can appreciate it as a window into the ever-changing processes that shape our planet. Nature’s earthquake swarm at Mt. Rainier serves as a reminder that the Earth beneath us is continually active and full of life, even in moments of apparent stillness.
