AVO reported that lava effusion continued at Great Sitkin during 22-28 September, though weather clouds sometimes prevented webcam and satellite views. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. By 24 September the dome had overtopped the S and W crater rims and flowed 305 m down the S flank and 195 m down the W flank. The dome was about 25 m thick and had grown to 1,170 m E to W and 925 m N to S in dimension. 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)