New in-depth study confirms Edgecumbe volcanic activity, earthquake swarm likely related

Mount Edgecumbe near Sitka in December 2004.
Mount Edgecumbe near Sitka in December 2004.(Duncan Marriott)
Published: Apr. 22, 2022 at 4:44 PM AKDT
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ANCHORAGE, Alaska (KTUU) - Seismic activity near Mount Edgecumbe is nearly back to background levels, according to the Alaska Volcano Observatory, but scientists have now completed an in-depth analysis that shows new information for the island near Sitka.

Geophysicists now believe the seismic activity — that started almost two weeks ago — is linked to magmatic activity in the volcano, which is considered dormant.

Scientists said the ground on the island is raising very slightly because the magma underneath it is making its way toward the surface. The uplift started in August 2018, according to the Alaska Volcano Observatory.

“We believe that the magma is pushing on the rocks underneath Edgecumbe enough to break some of them and cause the seismicity that we see,” said Geologist Cheryl Cameron with the Alaska Division of Geological and Geophysical Surveys.

However, this activity does not mean an eruption is looming.

“It hasn’t erupted in hundreds to thousands of years,” Cameron said. “We would expect to see lots more evidence of unrest before an eruption.”

Cameron said that would likely include very noticeable earthquakes. According to the Alaska Volcano Observatory, all quakes detected under the volcano since 2020 have been a magnitude 3.0 or smaller.

“The ground underneath Edgecumbe doesn’t have what we call an open conduit,” Cameron said. “You know, it doesn’t have this space where magma has an easy pathway to the surface like happens at some volcanoes that erupt frequently, which allows them to erupt. ... The magma in this case is going to have to physically break the rock to get to the surface of the volcano, and that will create earthquakes that are noticeable on seismometers.”

She said there is no reason to be concerned. However, it is always important to be prepared for any type of natural disasters.

“We are making plans to see what we can do about instrumenting Edgecumbe,” Cameron said. “Edgecumbe, of course, is within the Tongass National Forest so we’ll need to work closely with the Forest Service.”

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