Nation/World

This normally quiet Cascades volcano has been trembling. Should the Pacific Northwest worry?

Among the snow-capped volcanoes of the Pacific Northwest, Mount Adams gets relatively little love.

There are more glamorous volcanoes to climb (Mount Rainier) or to ski (Mount Hood) or that have exploded in epically dramatic fashion in living memory (Mount St. Helens).

Seismically, Mount Adams, located in southern Washington state, is relatively calm. The U.S. Geological Survey considers it a “high threat” volcano, but that’s a step below its “very high threat” neighbors, including all of those above.

Earthquakes are normally detected around Mount Adams once every couple of years, while Mount Rainier could have some 10 to 20 earthquakes per month, said Jon Major, scientist-in-charge at the Cascades Volcano Observatory.

So the alert earlier this month by the USGS that there has been a flurry of earthquakes around Adams got some attention from volcano watchers. There have been 10 earthquakes recorded there so far this year, including six in September and one this month, Major said, something he described as “a little out of character for this volcano.”

Does this mean it’s going to blow?

“Right now, there’s no cause for concern,” Major said in an interview.

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The recent earthquakes have been small - ranging from magnitudes of 0.9 to 2.0 - but the federal government has only one seismometer in the vicinity of Mount Adams, the second-tallest volcano in Washington state, so it is difficult to get precise information about their locations and depths. The agency is using the recent rumblings as an opportunity to learn more about this sometimes overlooked volcano.

USGS personnel have installed three new temporary seismic stations on Mount Adams, Major said.

“If they start to pick up more earthquakes, or if earthquakes start to get larger - if they start to be shallow and more frequent - then we would probably start to take a closer look,” he said.

Other potential signs of trouble have so far not materialized. The latest satellite imagery shows no bulging or deformation of the mountain from magma moving to the surface. And Mount Adams has not been spewing gases.

“We would want to see other symptoms before we got particularly concerned about the earthquakes,” he said.

When there has been volcanic activity at Mount Adams in the past, it is generally erupting lava flows, not in explosions such as the one that rocked Mount St. Helens in 1980, the most destructive volcanic eruption in U.S. history.

Over the past 12,000 years, there have been four lava flows from Mount Adams, and its last eruption occurred between 3,800 and 7,600 years ago, according to USGS.

The main threat to people these days from Mount Adams is volcanic mudflows, known as lahars, which in the past have reached the area where the small town of Trout Lake, Wash., is now.

Major said the recent earthquakes are “a little bit unusual,” but nothing that has happened so far is a cause for alarm.

“Just because we see an increase in the number of earthquakes doesn’t necessarily portend anything is imminent or about to happen,” he said.

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