Is Mt. Rainier About To Blow? Earthquake Swarm At Volcano Continues

A swarm of earthquakes under the largest volcano in the Cascade Mountain Range has some people wondering if it's rumbling back to life again.

This week, the U.S. Geological Survey (USGS) and the University of Washington say they have recorded over 400 small tremors beneath Mount Rainier.

The temblors began on Tuesday at around 1:29 a.m. and initially lasted for over 12 hours into the mid-day.

Scientists say the swarm was more protracted than those which are typically detected beneath the volcano once or twice annually.

The largest of the Tuesday quakes registered a magnitude of 1.7 on the Richter scale, and since then, at least 60 more tremors have shook the mountain, including a magnitude 2.3 that struck at 9:03 a.m. on Wednesday.

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The USGS says although earthquake activity around the mountain has been unusually high over the past day, there are currently no signs of an impending eruption, including ground deformation or changes in steam and gas emissions.

In an official statement regarding the quake swarm released on Tuesday, the USGS said, “Earthquake swarms like this have been attributed to circulation of hydrothermal fluids that are interacting with pre-existing faults at shallow levels below the summit of the volcano.”

This week's swarm, which appears to be ongoing, is the largest at Mount Rainier since September, 2009, when hundreds of temblors were recorded over a three-day period, including the largest of a magnitude 2.3 - which was matched during this week's swarm earlier this morning.

The 14,411-foot peak is considered by many scientists to be the most dangerous volcano in the Cascades, due to its proximity to major population centers, eruption history, and potential to produce large-scale eruptive events.

One of the biggest concerns surrounding a future eruption of Mount Rainier (which is a matter of "when" and not "if", by the way) is its possibility of producing devastating lahars.

Lahars are fast-moving flows of super-heated mud and debris that are created when the heat from a volcanic eruption causes the rapid melting of glacial ice. And Mount Rainier has a history of producing substantial lahars, even as recently as 500 years ago when an event known as the Electron Mudflow covered an area of 13 square miles on the present-day Puyallup Valley with as much as 26 feet of volcanic mud as far as 34 miles away from the mountain.

Other lahars at Mount Rainier, including one known as the Osceola Mudflow that occurred 5,600 years ago, have cut paths as long as 70 miles from the volcano and buried the landscape in over 300 feet of mud before spilling into Puget Sound. If such an event were to happen today, it would easily reach and completely engulf towns like Enumclaw, Fife, Orting, and Sumner, as well as major cities like Tacoma and even portions of Seattle.

Mount Rainier has also had eruptions which produced pyroclastic flows roughly 1,100 years ago, and large lava flows about 2,200 years ago. There are also reports of the volcano producing numerous steam eruptions as recently as the 19th Century, but many of these lack any geologic evidence.

The mountain is the most-heavily monitored in the world, and has been outfitted with a wide array of sensors and detection equipment that's designed to pick up even the smallest of changes in a variety of conditions both outside and inside the volcano.