Scientists raise alert level on Mount Spurr after seismic activity, signs of unrest

The Alaska Volcano Observatory raised the alert level of Mount Spurr to yellow Wednesday, after detecting increasing seismic activity and other signs of unrest.

Mount Spurr is the closest volcano to Anchorage, located 75 miles west of the city. Starting in April, scientists saw “a gradual increase in volcanic unrest at Mount Spurr over the past several months,” the Alaska Volcano Observatory said in a statement.

The changes include more earthquakes, signs of “sustained upward and outward ground deformation” and the development of a small lake in the usually ice-and-snow-covered summit crater over the summer, the statement said.

Then on Oct. 9, scientists located 63 small earthquakes beneath Spurr, said Matt Haney, scientist-in-charge at the Alaska Volcano Observatory. The swarm was “one of the factors in our decision to elevate the color code and alert level,” he said.

Despite the increased activity, “there are no indications an eruption is imminent,” Haney said.

Mount Spurr is known to have erupted in 1953 and in 1992, from a vent about 2 miles from the summit. During the 1992 eruption, up to a quarter inch of ash fell on Southcentral Alaska. The airport was closed for 20 hours.

It was a memorable event: A Daily News story from the time described how “ash was falling like rain” while “street lights flickered on a sulfurous smell hung in the air.”

““It looks like midnight in the middle of winter,” one Anchorage woman told the newspaper.

The volcano was last on yellow alert status in 2004, when earthquakes increased, heat melted a hole in the ice cap atop the summit of the volcano and scientists documented debris flows.

The biggest hazard posed by a potential eruption of Mount Spurr would be an ash cloud that could be blown into populated areas by wind and disrupt aviation routes, Haney said. Mud and debris flows could reach all the way to Cook Inlet, but wouldn’t be expected to move through populated areas of infrastructure, he said.

“It is very likely that if an eruption were to occur it would be preceded by additional signals that would allow advance warning,” the observatory statement said.

The volcano is heavily monitored with seismic, infrasound, web cameras and other instruments on the volcano, Haney said.