Alaska Volcano Observatory fully activates monitoring network over Sitka's rumbling mountain Seismic activity at Mount Edgecumbe has declined since a 2022 swarm of earthquakes, but a risk remains

Sitka's Mount Edgecumbe volcano is wired.

On Jan. 26, the Alaska Volcano Observatory announced the completion of a new instrument network intended to measure the activity of a volcano that could be awakening after a period of dormancy.

The network includes four seismic stations and four sites that measure the way the ground is deforming as magma moves deep below the volcano. Since April 2022, the movement of that liquefied rock has caused hundreds of small earthquakes and raised concerns that Sitka, 15 miles away, could soon be near an eruption.

That's still an unlikely scenario, and the new instruments - many installed last summer and evaluated over the winter - will keep track of the risk.

"It does have some signs of unrest - there's signs that there is magma that's come into the system very deep. We're talking 6 miles below the volcano. And so we want to be sure to be monitoring it as best we can," said Hannah Dietterich, a research geophysicist for the U.S. Geological Survey at the Alaska Volcano Observatory.

Mount Edgecumbe, a scenic, Mount Fuji-like volcano visible from Alaska's first capital city, hasn't erupted within written history, but Tlingit oral tradition notes some eruptions about 800 years ago, and the original name of the peak is L'úx Shaa, or "blinking mountain."

A 2010 research paper noted evidence of an ash eruption about 1,150 years ago, including deposits in Sitka Sound. A similar eruption "may pose significant risk to local population centers," the authors noted.

After a series of small earthquakes in 2022 drew attention to the volcano, experts reviewed satellite radar measurements from as far back as 2014 and concluded that ground near the mountain was bulging outward at a rate faster than seen at any other volcano in Alaska.

That growth has since slowed.

"The deformation rate has slowed in the last year, especially in the second half of 2023," Dietterich said.

The new instruments will help track any future changes in the volcano. Precise ground sensors mean that scientists can get hourly changes in the shape of the ground near the volcano instead of waiting days or weeks for less-accurate satellite measurements.

Seismic instruments installed near the volcano will give precise recordings of earthquakes smaller than magnitude 1. Before the new installation, the nearest instruments were in Sitka, and precise calculations were difficult.

"Often, the earthquakes you get at a volcano aren't usually the ones that anyone feels," Dietterich said. "When we have more seismometers on a volcano, we're able to see any movement of fluid or magma, or even faulting - structural things that can produce very, very small earthquakes."

That sensitivity means "we're much more able to essentially detect eruption precursors," she said.

Last summer, scientists also investigated reports of gas bubbling from the ground near the volcano. They took samples and submitted them for review, looking for signs that the gas was associated with magma deep underground.

"They just got the helium results this week," she said on Friday, "so hot off the presses. And it looks like there's no strong evidence for a volcanic signature to any of the gasses."

If there had been a signature, that could have been a sign of a path between the surface and magma deep underground, increasing the likelihood of an eruption.

In addition to providing early warning for Sitka, the new instruments will offer some research opportunities as well. Alaska's active volcanoes are generally located west of Anchorage, where the Pacific tectonic plate is sliding beneath the North American plate in what's known as a subduction zone. Edgecumbe, now the easternmost monitored volcano in Alaska, is near a transform fault, where the plates are sliding past one another. Less is known about volcanoes along transform faults, Dietterich said.

Some field maintenance is scheduled in May 2024 to improve the sensors and radio communications as needed, Dietterich said, and there is the possibility of later season geology work, but that hasn't yet been scheduled.

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