An eruption is possible at Alaska’s Mount Spurr. What we know about the volcano

Experts say there’s a 50-50 chance the volcano will erupt.

(CNN) — A volcano near Alaska’s most populous city could be on the brink of eruption after showing signs of unrest over the past 10 months, according to experts.

Hundreds of small earthquakes have occurred beneath Mount Spurr, located in the volcanically active Aleutian Arc and approximately 75 miles west of Anchorage, according to the Alaska Volcano Observatory, which tracks volcanic activity across the state.

Experts have also observed ground deformations, said David Fee, a coordinating scientist at the Alaska Volcano Observatory.

“Basically, as we think magma and fluids rise within the earth, it causes the ground to swell or deform,” Fee told CNN Saturday. The rising magma and other moving fluids can heat up surrounding areas on the way to the surface, according to Fee.

“These are our two key longer-term observations telling us that something is going on underneath,” Fee said, adding changes at Mount Spurr’s summit have also alerted scientists to the potential threat of an eruption.

“A small lake has formed within the crater, and there’s some warmer water and gas coming out as well,” he said.

Despite these signs, there is no way of telling when or if the volcano will erupt within a matter of days, weeks or months, according to experts.

There would likely be increased signs leading up to the eruption, like raised water temperatures and melted snow and glaciers. All scientists can do, however, is keep monitoring closely.

“We use a lot of our knowledge from past eruptions to kind of see what we think might happen in the future,” Fee said.

How significant is the risk?

As of now, experts say there’s a 50-50 chance the volcano will erupt.

Because there are no communities or cities in the volcano’s vicinity, “there’s no kind of local threat,” Fee said.

The main two hazards of a volcano eruption would be ash clouds that could impact air travel and potential ash fall over regional communities, including Anchorage’s, according to Fee.

“One or more explosive events lasting one or a few hours would produce ash clouds carried downwind for hundreds of miles, and the uninhabited area around Mount Spurr would be inundated by pyroclastic flows, mudflows, and ballistic showers,” the observatory said in a February 6 statement.

As of February 15, the observatory listed Mount Spurr’s volcano alert level at advisory, one step above normal.

“Spurr, at least in the past, has provided a longer run-up and more kind of warning signs before an eruption,” Fee said. “We’re looking at the data really closely for Spurr to see if any changes that might (suggest) that eruption is more likely are coming soon.”

When did Mount Spurr last erupt?

Mount Spurr erupted once in 1953 and three times in 1992, according to the observatory. Both years saw eruptions at the Crater Peak vent, located two miles south of the volcano’s summit.

“These eruptions were relatively small but explosive, and they dispersed volcanic ash over areas of interior, south-central, and southeastern Alaska,” according to a report on seismic activity at Mount Spurr by the US Geological Survey.

In 1953, the columns of ash the explosions produced rose up to 65,000 feet above sea level and deposited about 6 mm of ash in Anchorage, according to the report.

One of the 1992 eruptions closed down the Ted Stevens Anchorage International Airport for 20 hours, and numerous air-quality alerts were issued for several days after the eruption.

A present-day eruption would likely happen at Crater Peak again, according to Fee.

“There has been no eruption from the summit of Spurr in thousands of years, … so that’s one of the reasons we think it’s more likely to erupt (from Crater Peak),” Fee said.

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