AVO reported that the lava dome at Great Sitkin continued to be active, growing in diameter from 250 m on 6 August, to 380 m three days later, and to 700 m by 16 August. Steam-and-gas plumes were periodically observed in webcam images, in satellite data, and by observers on the ground during 11-17 August. Elevated surface temperatures and small earthquakes detected daily were consistent with the growing dome. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Geological Summary. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an older edifice and produced a submarine debris avalanche. Deposits from this and an even 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. 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 northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Eruptions have been recorded since the late-19th century.

Source: US Geological Survey Alaska Volcano Observatory (AVO)