AVO raises Gareloi volcano to Yellow/Advisory after brief explosion

The Alaska Volcano Observatory raised the alert level at Gareloi volcano in the western Aleutians after a brief explosion Thursday morning. The observatory moved the aviation color code from Green to Yellow and the volcano alert level to Advisory.

The Yellow code signals volcanic unrest above known background levels. It applies to aviation. The Advisory level, defined the same way by the U.S. Geological Survey, covers ground hazards. AVO says the main hazard from Gareloi eruptions is airborne ash that could affect aircraft.

The explosion lasted less than a minute. AVO detected it in geophysical data at 7:27 am Alaska Daylight Time on Oct. 1. The nearest community, Adak, sits about 93 miles east.

Clouds up to about 20,000 feet hid the volcano, so AVO does not know whether the explosion produced ash. The observatory said any ash "would be minor due to the short duration (less than 1 min) of the explosion."

Infrasound data indicated the explosion likely came from the volcano's south crater. On Friday, AVO said satellite radar showed a small crater-like feature near the fumarole field on the south flank.

Gareloi rises 5,161 feet. AVO says the volcano steadily releases magmatic gases and commonly shows low-level earthquake activity, a pattern that suggests shallow magma interacting with a hydrothermal system.

AVO said the explosion "likely reflects a change to the magmatic-hydrothermal system, but it is not clear that the likelihood of a volcanic eruption has increased." The observatory will keep monitoring to determine whether new magma is involved.

Updates Saturday and Sunday reported no further signs of unrest. On Sunday, AVO said wind noise had limited its seismic and infrasound detection and clouds had blocked satellite views. Gareloi remained at Yellow and Advisory as of that update.

Gareloi has had 16 reported eruptive events since 1760. AVO says a major explosive eruption in 1929 formed 13 craters along a fissure. A crater lake seen in 1949 suggested active acid fumaroles.

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

AVO posts updates on its Gareloi volcano page.