alaska volcano observatory

An explosion at one of Alaska's most active volcanoes has led scientists to raise its alert level to "watch." This comes after the Alaska Volcano Observatory (AVO) lowered Cleveland Volcano's alert level in early May after nearly a year and a half of inactivity.

Cleveland is located on an uninhabited island in the central Aleutians, west of Umnak Island. Around 10:30 p.m. on Monday, the AVO detected a small explosion that sent an ash plume 22,000 feet, traveling to the south.

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.

After two months of activity, Pavlof Volcano has been downgraded to a "normal" alert level.

The Alaska Volcano Observatory (AVO) issued an "advisory" for the volcano — which is located about 35 miles from Cold Bay — in December. But over the past several weeks, seismic activity steadily decreased.

The last observable sign was what the AVO calls "minor steam emissions," which occurred in late February. Since then, there have been no signs of activity at the volcano. 

Following a series of flight-canceling explosions, activity at Shishaldin Volcano has decreased over the past three weeks.

Matt Haney, a geophysicist with the Alaska Volcano Observatory (AVO), said this marks a pause for the eastern Aleutian volcano's eruptive phase, which has been underway since late last year.

A magnitude-6.2 earthquake struck Wednesday night about 50 miles from Adak.

"To give you an idea of how large that is, you get only about 100 magnitude-6 earthquakes on the globe annually," said seismologist Ken MacPherson of the Alaska Earthquake Center. "So that's a fairly significant earthquake."

Adak residents felt the shallow earthquake, which followed a series of smaller quakes in the same area.

MacPherson also said there have been dozens of aftershocks.