Updated 06/15/2020 at 7 p.m.
A magnitude-4.2 earthquake occurred under Makushin Volcano Monday afternoon and was felt in Unalaska.
At around 2:16 p.m., an earthquake at a depth of about five miles hit approximately six miles southeast of the volcano's summit, according to the Alaska Volcano Observatory. Small aftershocks are continuing, as is typical for an earthquake of this size.
"This is a pretty unusual earthquake at Makushin. There is earthquake activity out there, but this is quite a bit larger than usual," said Dave Schneider, a research geophysicist with the AVO. "Typically, a volcano's earthquakes are small — in the magnitude of around one. So four is a pretty good-sized earthquake. It's still too early to tell whether or not this particular one is related to something volcanic or if it's just a garden variety tectonic earthquake."
As of Monday afternoon, there had been 8 "felt reports" from Unalaskans on the United States Geological Survey (USGS) website.
The AVO said in a statement Monday evening that over the past several hours, there have been two earthquakes larger than magnitude 4 in the vicinity of Makushin Volcano, prompting scientists to raise the volcano's alert level to "advisory."
"This represents a significant departure from background earthquake activity and may be associated with volcanic unrest," said the statement. "As a result the Aviation Color Code and Volcano Alert Level has been increased to 'yellow/advisory.' This unrest could result a future eruption, however that is not a certainty."
Makushin Volcano is located on northern Unalaska Island about 16 miles from the community of Unalaska. According to Schneider, while scientists are still a long way away from thinking an eruption could happen, the greatest hazard an eruption would pose to the community and port of Unalaska/Dutch Harbor would be through ash fallout.
"Makushin is an active volcano. There's no getting around that," said Schneider. "There's a summit, degassing goes on up there in the snow and ice pack, there are hot areas that have had sulfur dioxide gas coming out — which is a typical volcanic gas — for quite a long time, and steaming is sometimes observed. So we would consider it to be an active volcano. And so, although it doesn't erupt that frequently, it is possible that this could lead to eruption. That's very speculative at this point, and we really need to see what comes to pass."
Makushin is well-monitored, said Schneider. If volcanic activity ramps up, scientists are in a good position to detect it with the monitoring network they have in place and are prepared to provide guidance to nearby communities.
There have been 20,534 earthquakes in Alaska so far this year. About 25% occurred in the Aleutian Islands.
"Certainly the Aleutians are seismically-active. You guys are right on the edge of the down going Pacific plate," Schneider said. "Earthquakes happen all along the Aleutian arc. This earthquake's location to Makushin is what makes it something that gets our attention. It's relatively shallow…tectonic earthquakes tend to be deeper. But it's too early to say whether or not this is related to some sort of new intrusion of magma into the volcano or not."
According to the Alaska Earthquake Center, Alaska has had a record number of seismic events in recent years. With a total of 50,289 reported earthquakes, 2019 finished as a runner up to the record-breaking 2018. The largest earthquakes last year were two magnitude 6.4 events: one on April 2 in the Rat Islands and one on Nov. 24 in the Andreanof Islands regions of the western Aleutians.