Several pilots reported a short-lived, explosive eruption of Bogoslof volcano in the Aleutian Islands that sent an ash cloud 34,000 feet in the air, according to the Alaska Volcano Observatory.
The pilots reported the eruption around 4 p.m. Tuesday. They estimated the altitude of the rising ash, according to AVO.
Observers said that satellite data showed a discrete, short-lived explosion just before 4 p.m. that sent ash drifting south. Another pilot who passed by nearly an hour after the explosion told the volcano observatory that activity had decreased.
— Alaska AVO (@alaska_avo) December 21, 2016
Still, AVO found it necessary to raise Bogoslof volcano's status to red and issue a warning alert status, which means a volcanic eruption is imminent, underway or suspected with hazardous activity on the ground and in the air.
Around 9 p.m., Bogoslof volcano's status was downgraded to orange, which means that the volcano "is exhibiting heightened or escalating unrest with increased potential of eruption" or that "an eruption is underway that poses limited hazards including no or minor volcanic-ash emissions."
According to the U.S. Geological Survey, Bogoslof Island is the largest of a cluster of small, low-lying islands that make up the summit of a large underwater stratovolcano. The volcano rises about 6,000 feet from the Bering Sea floor, but is only 300 feet above sea level at its highest point.
There is no ground-based monitoring equipment on Bogoslof volcano, which is located slightly north of the main Aleutian volcanic front, USGS scientists noted in a report about the eruption.
"AVO is unable to provide a forecast of future eruptive activity. We will monitor satellite images and data from distant seismic and infrasound instruments for indications of significant explosive activity," the report says.