A magnitude 3.5 earthquake occurred at Great Sitkin Volcano on Friday.
Since then, seismic activity has returned to lower levels, and no eruptive activity has been detected at the volcano – located 26 miles east of the community of Adak.
Hans Schwaiger, a scientist with the Alaska Volcano Observatory (AVO), said it appears the shallow earthquake was an isolated event, although small local earthquakes have continued over the past day.
"There's been an increase in seismic activity over the past week," said Schwaiger. "It was maybe about eight or nine days ago that we increased the color code to yellow because of the increase in the earthquakes."
Schwaiger said the AVO is closely monitoring the volcano for other signs of unrest that may indicate increased activity or likelihood of an eruption.
Great Sitkin erupted at least three times in the 20th century, most recently in 1974.
"That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft above sea level," said the AVO in a statement.
The current alert level for the volcano is "advisory" and the aviation color code is "yellow."
There are no reports that Friday's shallow earthquake was felt in nearby Adak.