With Mount Edgecumbe in the background, a sea lion pops its head out of the water next to a buoy crowded with other sea lions in this 2018 file photo. A swarm of hundreds of small earthquakes were reported near the Mount Edgecumbe volcano 15 miles west of Sitka. The reason for the swarm is not known, officials at the Alaska Volcano Observatory said.
The Alaska Volcano Observatory said that as of last Thursday the number of earthquakes under Mount Edgecumbe was declining.
The earthquake activity is beneath the 3,000-foot high dormant volcano 15 miles west of Sitka on Kruzof Island.
The volcano observatory sent out an information statement a day earlier about the "swarm" of small earthquakes under Mt. Edgecumbe, with an accompanying message that there is no cause for alarm by the public.
"We're getting information out and trying not to alarm people," said David Schneider, a research geophysicist at the Anchorage volcano center.
Thursday's report from the U.S. Geological Survey observatory said the earthquakes started at 2 a.m. April 11, and since then hundreds of small quakes, "a swarm," have been detected, although "the large majority are too small to locate."
The Alaska Earthquake Information Center said the largest reported earthquake occurred at 11:04 a.m. April 11 with a magnitude of 2.8 at 6.2 miles depth. The observatory center said the rate declined over the week.
Jacyn Schmidt, geoscience coordinator at the Sitka Sound Science Center, said there is no indication that an eruption "is imminent or will happen at all."
"It would take a lot more activity beneath the volcano," she said.
The Anchorage volcano observatory is a cooperative program of the U.S. Geological Survey, University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.
Schneider said there are no plans to install additional instruments in Sitka, but that would be reevaluated if the earthquake activity continues or increases. He said University of Alaska Fairbanks scientists are analyzing synthetic aperture radar satellite data "which could be used to monitor any deformation that happens."
The analysis can tell scientists how the ground is moving over time, from year to year or week to week, and it is a common method used for analyzing volcanic deformation, movement during earthquakes, and land subsidence through groundwater withdrawal.
Mount Edgecumbe is classified as a "stratovolcano," part of a broader volcanic field of lava domes and craters on southern Kruzof Island and surrounding submarine vicinity. There are no written observations of eruptions from the volcanic field, but Tlingit oral history describes small eruptions that occurred about 800 years ago.
The last Mount Edgecumbe eruption preserved in the geologic record was about 4,500 years ago.
There's also evidence of a large eruption 13,000 to 14,500 years ago where up to 3 feet of ash was deposited on what is now Sitka, while 98 feet fell on Kruzof Island.
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