Mount Rainier - earthquake swarm July 2025

[Astronuc]

Small earthquakes are not new at Mt. Rainier, but a recent swarm of more than 1000 earthquakes is unusual.

https://www.kiro7.com/news/local/mo...est-ever-recorded/UNHHMV3ECBFGRP2WIHN4NJDCXU/

MOUNT RAINIER NATIONAL PARK — An earthquake swarm at Mount Rainier that started on July 8 is considered one of the largest ever recorded for the volcano, according to the United States Geological Survey (USGS).

An earthquake swarm is a cluster of seismic activity or earthquakes that occur one after another.

So far, the largest earthquake in the swarm happened on July 11 and was no larger than 2.4 in magnitude.

By Friday (July 25), seismologists with the Pacific Northwest Seismic Network had located 1010 earthquakes.

https://www.usgs.gov/observatories/...ll-magnitude-earthquakes-mount-rainier-during

https://pnsn.org/blog/2025/07/18/mount-rainier-earthquake-swarm-of-july-2025

 

[fresh_42]

I've recently seen a documentary about the Phlegrean Fields. They said that a swarm of many low magnitude earthquakes can be more worrying than a single larger one as a predictor of a coming outbreak. And I think Mt. Rainier counts as active.

 

[Astronuc]

And I think Mt. Rainier counts as active.

Yes, Mt Rainier is active. There are occasional releases of steam from thermal vents.
https://www.nps.gov/mora/learn/nature/volcanic-features.htm

Its sibling, Mt. St. Helens also had numerous swarms before it catastrophically erupted on May 18, 1980.

Seismicity at Mount St. Helens is quite variable depending on the volcano's eruptive state. Most earthquakes are located at a shallow depth directly under the volcano; however there is a St. Helens Seismic Zone (SHZ) that extends north and south of the volcano on which some earthquakes take place. Seismicity changes character just before eruptions begin. There is usually an increase in both number and size of earthquakes as well as a change in the character of the seismograms. Such changes were detected and recognized as precursors to most of the two dozen or so eruptions during the past 30+ years including a two month precursory sequence before the cataclysmic eruption of May 18, 1980.

https://www.pnsn.org/volcanoes/mount-st-helens#seismicity