Scientists have detected a ‘modest’ uptick in seismic activity at Mount Rainer, with more than 20 earthquakes rumbling near the active volcano in the last week alone.
While the site typically experiences a few sizable tremors per week, the experts say the current rate is higher than usual.
But, for now, there’s little cause for worry.
In the last decade, Mount Rainer has seen similar and even more active swarms, all likely tied to processes in the volcano’s hydrothermal system.
The current swarm started September 11, with five earthquakes located 1-2 km (0.5 to 1.5 mi) to the southeast of the summit area. The stations then detected earthquakes about 1 km (0.5 mi) to the northeast and southeast of the summit starting September 13
Since last Monday, the Pacific Northwest Seismic Network has detected a total of 23 earthquakes at Mount Rainier, with as many as eight located earthquakes per day.
A ‘located’ earthquake is one large enough to be recorded on at least four seismic stations, according to the US Geological Survey.
This area usually experiences two located earthquakes each week, meaning this week’s activity is undeniably higher than normal.
Still, it is not unprecedented, the experts assure.
‘Swarms are a common and expectable occurrence at active volcanoes such as Mount Rainier,’ USGS explains.
‘While interesting, most never result in surface changes.
‘The most likely scenario for the current swarm is that elevated earthquake rates will continue for a few days before slowly decaying to background rates of seismicity.’
The current swarm started September 11, with five earthquakes located 1-2 km (0.5 to 1.5 mi) to the southeast of the summit area.
Each were small, with the largest being a magnitude 1.6, and took place up to 2 km (1.5 mi) above sea level.
The stations then detected earthquakes about 1 km (0.5 mi) to the northeast and southeast of the summit starting September 13, at 1-2 km (0.5 to 1.5 mi) below sea level.
According to the experts, this is typical for earthquakes at Mount Rainier.
Previously, the stations have recorded three swarms of above-average activity, in September 2009, April 2015 and May 2016.
In the last decade, Mount Rainer has seen similar and even more active swarms, all likely tied to processes in the volcano’s hydrothermal system. While it may not be a worry for now, experts say the volcano is one of the most dangerous in the world
The rates seen now are similar to those in 2015 and 2016, according to USGS, but smaller than the 2009 events.
During that time, there were hundreds of located earthquakes in a span of just three days.
According to USGS, processes in the hydrothermal system are probably to blame for the past and present events.
‘The hydrothermal system is the region beneath the volcano containing hot mineral-rich water; one manifestation of this system is the boiling-point fumaroles that are found at the volcano’s summit,’ USGS explains.
‘Similar to pipes in geothermal plants, cracks transporting water away from a hot source may seal shut as the water cools and loses its dissolved minerals.
‘Earthquakes are created when sufficient fluid pressure builds behind these seals to fracture them.’