The Alaska Volcano Observatory is planning to install a series of seismic instruments on Mount Edgecumbe near Sitka after preliminary measurements showed magma moving deep below the Mount Fuji-shaped volcano.
The movement doesn’t mean an eruption will happen soon — or even at all — from Southeast Alaska’s most prominent volcano, but it’s significant enough that the observatory has raised the volcano’s threat level.
“Internally, how we think about Edgecumbe has changed. It definitely has moved up,” said Cheryl Cameron, a state geologist who works at the volcano observatory.
Officials at the observatory have been paying greater attention to Edgecumbe since April last year, when a swarm of small earthquakes brought attention to the volcano, which had been considered dormant.
A new information update, released Friday, shows the earthquakes have continued, hikers have observed gas bubbling from the ground near the volcano, and satellite radar measurements show the ground around the volcano bulging upward.
“Our latest update is really just saying, ‘Hey, this unrest is still going on. We still think the magma is very deep. It might not erupt. If it does erupt, we expect a lot more activity before that happens,’” said Michelle Coombs, a USGS geologist and scientist-in-charge at the Alaska Volcano Observatory.
In an October paper published in the journal Geophysical Research Letters, scientist Ronni Grapenthin noted that the ground on the east side of the volcano was bulging outward at a rate faster than any other volcano in Alaska.
“Other volcanoes have had similar amounts of deformation without erupting,” Coombs said, noting that the ground around Laguna del Maule in Chile has been bulging outward even more quickly than Edgecumbe, and for a longer period, without an eruption.
Mount Edgecumbe is now considered a “high” risk volcano, one step below the state’s “very high risk” volcanoes: Augustine, Spurr, Redoubt, Akutan and Makushin.
Risk isn’t just the likelihood of an eruption, Coombs said. It’s also based on how close a volcano is to homes, businesses and structures.
Mount Rainier, in Washington state, hasn’t erupted in more than 500 years and shows no signs of doing so, but it’s the No. 3 risk in the nation because of its threat to the people living nearby.
There are no written accounts of eruptions from Mount Edgecumbe, but Tlingit oral tradition calls L’úx Shaa (the original name of Edgecumbe) “a mountain blinking, spouting fire and smoke” about 800-900 years ago.
Scientific core samples indicate eruptions about 4,000 and 4,300 years ago, with additional eruptions before that.
“To a geologist, erupting 4,000 years ago is pretty recent, you know?” Coombs said.
A series of eruptions about 14,000 years ago spread volcanic ash across Southeast Alaska that may have helped melt the glaciers that covered the region at the time.
Now, 73,000 people live in the region. Sitka, with a population of about 8,400 people, is 14 miles away.
Don Kluting and his wife, Denise Turley, are among those 8,400 people and frequently travel across Sitka Sound to Kruzof Island, home to Mount Edgecumbe, for hikes and birding.
In October, they found something new — gas bubbling through several ponds on the east side of the island.
Turley said their first thought was that the bubbles were from something decomposing in the ponds or from tidal action, but they’d never seen them before and thought the bubbles remarkable enough to report them to Cameron, who is Tlingit and from Sitka.
That report inspired the volcano observatory to plan a gas-sampling mission, which could take place as early as May. If the gas bubbling through the lakes is magmatic, she said, it’ll be another sign of activity at the volcano.
About the same time, the observatory will be placing three or four additional instrument stations on the volcano.
These stations will use GPS to track the volcano’s continued expansion, and their seismographs will allow scientists to triangulate the small earthquakes that take place within the volcano as magma moves around.
Cameron said the observatory is also planning a meeting with Sitka residents to explain what’s going on with the volcano.
Partially because of their experience, Kluting and Turley have been following events more closely than most. They said they’re not concerned by the volcano’s movement or the distant prospect of an eruption.
“I guess I trust the science on it,” Kluting said. “I have certainly heard from people that are very concerned and feel like they’re scared. After talking with Cheryl and crew, I think that the monitoring works. I think the science is behind it. I think they’re doing due diligence and following through and they believe there’s going to be lots of warning if we ever get to that point, and it may never happen.”
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