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Swarm of small quakes rumble under Mount Hood

Dozens of temblors recorded since Sunday night


USGS - A series of small quakes began Sunday night and continued through Monday on Mt. Hood.A swarm of small earthquakes is shaking the ground beneath Mount Hood near Government Camp.

The quakes began on Sunday night and continued through Monday. The first was detected at 6:17 p.m. on Sunday, and had a magnitude 1.1 at a depth of 4.3 kilometers. Dozens of small quakes followed through Sunday night, Monday morning and into Monday afternoon, all of which were less than 1.9 in magnitude and recorded at a depth of 4.9 kilometers or less.

Bill Steele, director of outreach and public information at the Pacific Northwest Seismic Network, described the quakes as no cause for concern. He said the swarm does not suggest volcanic unrest.

“This is an area where we’ve had earthquakes in the past,” Steele said. “It is associated with an area of crustal weakness.”

Mount Hood’s tiny quakes differ from the earthquake swarms that have put Washington's nearby Mount St. Helens in the news recently. There, Mount St. Helens’ earthquakes are helping to re-inflating the magma chambers in the shallower parts of the volcano, which is part of its natural eruption pattern.

While he can’t be certain, Steele said Mount Hood’s earthquakes could be triggered by geothermal fluids moving in one specific spot. In other words, it’s the same tiny earthquake happening over and over again.

“They have a characteristic signature,” he said. “They’re happening very close to each other.”

The quakes are clustered south of the summit of Mount Hood, near to where highways 26 and 35 meet. But given the small size of the quakes, residents of the area should continue their daily activities as usual, probably without any noticeable interruption.

“I would be surprised if any of them are felt,” Steele said of the quakes.

A list of the quakes is available to the Pacific Northwest Seismic Network's website.