By GARLAND KENNEDY
Sentinel Staff Writer
Seven months after an earthquake swarm beneath Mt. Edgecumbe led volcanologists to determine that the volcano is active, data collection and research are continuing.
Since August 2018, magma has risen beneath the formerly dormant volcano and caused about 7.1 centimeters of deformation annually, University of Alaska Fairbanks associate professor of geodesy Ronni Grapenthin said.
An eruption is not imminent, he added.
Mt. Edgecumbe volcano is pictured in April. (Sentinel File Photo)
Since April’s quakes, seismic activity on the mountain has subsided, he noted, but the mountain is deforming more quickly than any other Alaskan volcano. Mt. Edgecumbe, or L’ux Shaa in Tlingit, is located about 15 miles west of Sitka.
“It’s a lot (of ground deformation) compared to other Alaskan volcanoes… We’ve had other volcanoes with similar pulses of deformation as Edgecumbe in the past, but those usually have been kind of short lived, not going on for that long. So it is, right now, the fastest deforming volcano in Alaska,” Grapenthin said over the phone.
In May, a team of scientists from the Alaska Volcano Observatory installed GPS and seismic sensors on the mountain in order to gather more detailed information.
Since activity began, magma has risen from about 20 kilometers beneath the surface to 10 kilometers, he said. For the time being, the professor sees no signs that shallower magmatic activity is taking place.
Prior to any eruption, he said, certain warning signs would be observable.
“For a volcano like Edgecumbe that hasn’t erupted in a long time, at least hundreds of years, we wouldn’t expect that there’s an established path to the surface,” he said. “So you would experience a lot of breaking of rock – the magma would have to break a lot of rock to make its way to the surface. And we’d see that especially now, with instrumentation on the volcano.”
Grapenthin characterized the current seismic activity beneath Kruzof Island as “background.”
“There was that swarm in April and that swarm subsided. So right now, it’s certainly back to what one might consider background… The April activity has basically subsided, it was a few days of swarm, a lot of stress was released and that has gone down again,” he said.
In a scientific paper published Oct. 10 by the American Geophysical Union, Grapenthin and his colleagues wrote the following:
“We believe that we are observing magma rising through malleable crust into an existing magmatic system and that the observed earthquakes are created as the overlying rock adjusts to the increased magmatic pressure. The observed activity is rare, especially in similar tectonic settings, and presents an opportunity to better understand the reactivation of dormant volcanoes.”
Grapenthin was grateful for the cooperation UAF received from the Sitka Sound Science Center and the Alaska Volcano Observatory.
For now, Sitka’s local volcano will remain under observation, though Grapenthin stressed that he sees no signs of imminent eruption. The next steps for UAF and AVO involve installing additional sensors and gathering data.
“There’s plans to expand the ground-based network to be able to add additional seismometers and ground motion sensors, et cetera. And then in terms of the science now, hopefully, we can try to do more detailed modeling of these observations that we have now. It is a fairly complex system with magma that is moving from 20 kilometers (below the surface) to 10 kilometers. And we have a rich data stream,” he said.
