MOUNT RAINIER—A total of 895 earthquakes have shaken the ground beneath Washington’s highest mountain since the beginning of July, according to the United States Geological Survey, but the Pacific Northwest Seismic Network said it’s nothing to worry about.
The “earthquake swarm” began on July 8, at approximately 1:30 a.m., and continues through Wednesday, July 23. The largest of these earthquakes was a 2.4 on July 11.
Currently the color-coded alert for Mount Rainier remains at green, for normal. The PNW Seismic Network is continuing to track each earthquakes’ location, size, and depth. Though the current count is 895, the USGS said it could be much higher after the Seismic Network concludes its tally.
The rate of earthquakes has been steadily decreasing since July 8 and as of Wednesday, July 23, there are only a “few earthquakes per hour,” the USGS said. The earthquakes are mainly spread between 1.5-4 miles (2-6 km) beneath the summit and are too small to cause damage or to be felt by those above.
Mount Rainier usually sees about nine earthquakes per month. The last earthquake swarm was in 2009 and lasted only three days. The ongoing swarm has far surpassed that in frequency, event rate, and energy release.
“Many people ask us ‘what is going on at Mount Rainier these days?’ While we can say an unusual number of earthquakes have occurred the cause of them is not known for sure,” said Steve Malone with the Seismic Network. “A good conceptual model for ‘why’ is that relatively minor changes in the hydrothermal (hot water) system at the core of the volcano have generated enough localized stress changes to break rock. Of course the breaking of rock causes shaking that we record as an earthquake.”
Seismic activity at Mount Rainier has been closely monitored since the early 1970’s but it wasn’t until 1990 when enough stations were installed high on the cone, allowing for more detailed detection and more accurate location of earthquakes, Malone continued.
The seismic network now has 20 seismic stations on or near the volcano today.
The last time Mount Rainier erupted is estimated to be over 1,000 years ago, though there were reports of volcanic activity throughout the 19th century.
According to the USGS, a Mount Rainier eruption would likely affect those living in the surrounding areas most of all, as well as tourists visiting the mountain and those flying above. It would also likely impact the scenic and natural resources that provide recreation, wildlife habitat, and water for drinking and power generation.
Affected areas could also be impacted by volcanic gas emissions, the USGS continued, driving them to take basic precautions of alert.
Seismologist theorize that an eruption would be noticeable first by steam and ash explosions at the summit, followed by effusions of small lava flows. Avalanches caused by the heating of the mountain, mudslides (lahars), pyroclastic flows (basically avalanches of hot rock and debris), and the triggering of additional earthquakes, are all causes of concern for those living in the valleys downstream from the volcano.
To receive updates on Mount Rainier’s seismic activity, you can sign up for USGS volcano notifications here: https://volcanoes.usgs.gov/vns/.
Author: Kienan Briscoe
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