Above-background activity has been observed at the Great Sitkin volcano in Alaska, prompting the Alaska Volcano Observatory to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on May 13, 2021.
Elevated surface temperatures have been observed in satellite images beginning in January 2021 and detections have increased over the past two months.
Satellite detections of increased volcanic gas emissions have been observed beginning on May 10.
In addition, there has been a slight increase in local seismicity over the past two days.
These data indicate a potential for increased eruptive activity at Great Sitkin, AVO said.
As a result, the observatory has raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory at 00:57 UTC on May 13, 2021.
The coastline on the west side of the Great Sitkin volcano on June 21, 2019. Image credit: Wyatt Mayo, AVO/ADGGS
Great Sitkin is monitored with a local real-time seismic network, which will typically allow AVO to detect changes in unrest that may lead to an explosive eruption.
Rapid detection of an ash-producing eruption would be accomplished using a combination of seismic, infrasound, lightning, and satellite data.
Great Sitkin forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km (0.5 - 0.7 miles) ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche.
Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp.
Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m (20 feet).
The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along the northwest- and NNW-trending lines.
Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano.
Historical eruptions have been recorded since the late-19th century.
Featured image: The coastline on the west side of the Great Sitkin volcano on June 21, 2019. Image credit: Wyatt Mayo, AVO/ADGGS