Mount Rainier has the shakes.
According to a report from the U.S. Geological Survey, the 14,410-foot mountain endured approximately 391 individual earthquakes between July 8 and July 11, marking the most seismically active period in the peak’s recorded history.
But don’t worry—scientists don’t think it’s a sign of anything bad. The USGS noted that not only are the quakes too small to feel underfoot, but “the shaking from these is too small to trigger any additional activity from cliff faces or glaciers,” such as rockfall or avalanches.
The earthquakes were first picked up by the seismographs at the Cascades Volcano Observatory in the early morning hours of Tuesday, July 8, and have continued for the past three days. Seismologists said the earthquakes are occurring in the earth’s crust, between two and four miles beneath the mountain. During it’s peak, the earthquakes were occurring 30 times an hour.
But these earthquakes are so minor that people cannot feel them. According to the USGS, the most violent one had a magnitude measurement of 2.3. Earthquakes below 2.5 are usually not even felt by human beings, though they can be picked up by seismographs.
Mount Rainier is the most heavily glaciated peak in the United States, and an active stratovolcano. Though it has not fully erupted in roughly 1,000 years, it is considered among the most dangerous volcanoes in the world due to its proximity to the densely populated urban area of Seattle. Rainier is one of just 16 volcanoes in the world to be on the “Decade Volcanoes” list, a classification created by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) to highlight volcanoes worthy of close monitoring because of the catastrophic effects of their potential eruption.
Earthquake swarms typically occur once or twice per year around Rainier; though these annual swarms usually involve far fewer overall quakes. Before this week’s swarm, the largest swarm recorded at Rainier occurred in 2009. It reached a magnitude of M2.5, but did not consist of as many individual quakes, or as much energy released.
Alex Iezzi of the USGS told KOMO News that the recent swarm “is the most significant event since we have been having monitoring equipment at Mount Rainier,” although, “we have to remember Mount Rainier is really old. We’ve only been monitoring it for 40, maybe 50 years now. So just because it’s the most significant one we’ve seen on equipment doesn’t mean this hasn’t happened in the past, prior to 2009.”
They also confirmed that this week’s swarm, which is likely caused by “water moving around the crust above the magma chamber,” does not indicate an increase in volcanic activity or raise threat levels. “Right now, this swarm is still within what we consider normal background levels of activity at Mount Rainier,” said the USGS. “The volcano is not ‘due’ for an eruption, and we do not see any signs of a potential eruption at this time.”
