Alaska Volcano Observatory raises Gareloi alert level after brief explosion

The Alaska Volcano Observatory raised the alert level at Gareloi volcano in the western Aleutians after a brief explosion Thursday morning. It moved the aviation color code from Green to Yellow and the volcano alert level to Advisory, the first for pilots and the second for hazards on the ground. Both signal unrest above known background levels. AVO says the main hazard from Gareloi eruptions is airborne ash that could affect aircraft.

The explosion, detected at 7:27 am, lasted less than a minute. Adak, the nearest community, is about 93 miles east.

Clouds hid the volcano, so AVO does not know whether the explosion produced ash. It said any ash "would be minor" because the explosion was short. Infrasound data indicated the explosion likely came from the volcano's south crater, and on Friday, satellite radar showed a small crater-like feature near the field of gas vents on the south flank.

The 5,161-foot volcano steadily releases volcanic gases and commonly has small earthquakes, a pattern AVO says suggests shallow magma interacting with hot groundwater. AVO said the explosion likely reflects a change in that system, "but it is not clear that the likelihood of a volcanic eruption has increased." The observatory is monitoring to determine whether new magma is involved.

Updates Saturday and Sunday reported no further signs of unrest, though AVO said Sunday that wind and clouds had limited its monitoring. Gareloi remained at Yellow and Advisory as of Sunday.

Gareloi has had 16 reported eruptive events since 1760. AVO says a major explosive eruption in 1929 formed 13 craters along a fissure.

Great Sitkin, another Aleutian volcano, remains at Orange and Watch. Lava has erupted slowly there since July 2021.