First things first — everything is normal. Mount Rainier is not about to erupt. Today, at least. (The future is another story).
Got it? OK, good. Now that is out of the way, the Cascades Volcano Observatory with the U.S. Geological Survey said Tuesday morning that a “swarm of earthquakes” had been detected at Mount Rainier starting around 1:30 a.m.
So far, hundreds of earthquakes have been detected with several occurring per minute with depths ranging between 1.2 and 3.7 miles below the summit. No earthquakes have been felt at the surface, according to USGS, and the largest earthquake so far has a magnitude of 1.7.
Every year, more than a hundred earthquakes are detected at or near Mount Rainier with an average of nine earthquakes per month, according to USGS. “Swarms” of earthquakes typically occur once or twice a year, but they usually have fewer events than what started Tuesday, according to USGS.
Superheated groundwater and gases (aka hot fluids) flow into an area of existing faults, triggering small movements, which are the earthquakes, said Harold Tobin, a professor at the University of Washington and the director of the Pacific Northwest Seismic Network.
The swarms are a sign that Mount Rainier has an active system of magma lying deep below.
So far, the swarm is not a source of concern. However, if the earthquakes move closer to the surface, or the volcano began to bulge in some spots, or release steam or gases from the surface, it might elevate concern that the volcano was entering into unrest, Tobin said.
Unrest means the volcano is showing signs of things like magma moving up inside the volcano. It includes unusual activity that could portend an eruption or a volcano that is actively erupting.
The last large swarm at Rainier occurred over a three-day period in 2009 with the largest magnitude being 2.3. That event had over 1,000 earthquakes. Swarms have generally been caused by “circulation of fluids interacting with preexisting faults,” USGS said in a news release.
The agency said instruments also do not reveal any ground deformation at the volcano, and there have been no unusual signals at infrasound monitoring stations. While Mount Rainier is an active volcano, the monitoring system in place should provide days, if not weeks, of warning if there is an impending eruption.
“Currently, there is no indication that the level of earthquake activity is cause for concern, and the alert level and color code for Mount Rainier remain at GREEN / NORMAL,” the USGS news release stated.
