By SHANNON HAUGLAND
Sentinel Staff Writer
Alaska Volcano Observatory in Anchorage reported today that “a swarm” of earthquakes has been detected under Mt. Edgecumbe volcano, starting at 2 a.m. Monday.
Mt. Edgecumbe is pictured from Mt. Verstovia with an ominous cloud forming over it on March 27. The Alaska Volcano Observatory said today that “a swarm of earthquakes” has been detected in the vicinity of Mt. Edgecumbe volcano, starting at 2 a.m. Monday.
(Sentinel Photo by James Poulson)
Officials at the U.S. Geological observatory said they have not assigned an alert level, but are monitoring the situation and see no cause for great concern at this time.
“Many volcanoes have seismic swarms that don’t lead to eruptions,” said David Schneider, research geophysicist at the observatory. “A volcano like Edgecumbe, which is dormant, would experience many, many earthquakes prior to an eruption if one were to occur. This would give additional time for warning the community and for emergency preparation ... We’re not trying to alarm people, we’re just trying to get the information out to them.”
Schneider said the greatest hazard to Sitka from an eruption would be ash fall, which disrupts a number of systems, particularly transportation and infrastructure.
Sitka Fire Chief Craig Warren said he is aware of the situation.
“From my aspect I’m planning on continuing to monitor, and keep an open dialog,” he said. “I’m not excited or overly concerned right now.”
The observatory’s statement said, “There have been hundreds of small quakes in the swarm, though the large majority are too small to locate.”
The National Earthquake Information Center reported that one of the largest earthquakes in the swarm occurred at 11:04 a.m on April 11, with a magnitude of 2.8 at 10 km depth. The Alaska Earthquake Center reported another earthquake occurred at 3:44 p.m. the same day, with a magnitude of 2.1 and depth of 4 km.
“As of this morning, the swarm continues, though the rate of earthquakes has declined over the past 24 hours,” the information statement said.
Schneider said seismic swarms can wax and wane, so the fact that they have declined does not mean they will not go back up again.
Jacyn Schmidt, geoscience coordinator at the Sitka Sound Science Center, told the Sentinel today that there that Mt. Edgecumbe has had earthquakes in the past, but no swarms have been associated with them.
“The important thing to highlight is that the number of events, while they are small, is unusual,” Schmidt said. “The Volcano Observatory (scientists) are going to continue to monitor this.”
Mt. Edgecumbe, the most prominent natural landmark around Sitka, is located 15 miles west of the town.
In today’s statement the Alaska Volcano Observatory said the cause of the earthquake swarm is unknown, but may be associated with volcanic processes, regional tectonic activity, or a combination of sources.
“Retrospective analysis of earthquake data in the area shows that a small number of earthquakes started occurring under Edgecumbe in 2020,” the statement said. “This week’s activity is unusual in the number of events, however.”
The observatory will continue to monitor the dormant volcano using regional seismic stations, in Sitka and elsewhere, and with satellite data. Because there is no local monitoring network, “no Aviation Color Code and Volcano Alert Level are typically assigned to the volcano; its status therefore remains unassigned.”
“Should activity increase AVO will issue further notices and possibly (assign) the aviation color code and volcano alert level,” the statement said.
The color codes for aviation are green, yellow, orange and red; and the volcano alert level for ground hazards are “normal,” “advisory,” “watch” and “warning.”
The AVO issued some general information about the volcano:
“Mt. Edgecumbe is a 976-meter (3,202-foot) high stratovolcano on Kruzof Island located 24 km (15 miles) west of Sitka, Alaska, and is part of a broader volcanic field of lava domes and craters on southern Kruzof Island and surrounding submarine vicinity.
“Mt. Edgecumbe and the surrounding volcanic field lies within the Tongass National Forest. There are no written observations of eruptions from the volcanic field; Tlingit oral history describes small eruptions from about 800 years ago. Geologic investigations show that eruptions 13,000 to 14,500 years ago produced at least one widespread regional tephra layer around 1 m thick near Sitka and over 30 m thick on parts of Kruzof Island. The youngest eruption preserved in the geologic record was about 4,500 years ago. The volcanic field has erupted a wide range of basalt to rhyolite compositions from numerous vents over the past 600,000 years.”
The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.
The news release cited these contacts for additional information:
http://www.avo.alaska.edu
http://www.avo.alaska.edu/color_codes.php for definitions of Aviation Color Codes and Volcano Alert Levels
http://volcanoes.usgs.gov/vns/ for email updates
Schmidt said those with questions may also call her at 650-464-7995.
