Ash emissions from the cone in Veniaminof’s ice-filled summit caldera significantly increased overnight during 20-21 November, prompting AVO to raise the Aviation Color Code to Red and the Volcano Alert Level to Warning (the highest levels on four-level scales). Ash emissions rose to below 4.6 km (15,000 ft) a.s.l. and drifted more than 240 km SE. On 21 November observers and webcam views in Perryville (35 km SE) indicated continuous ash emissions through most of the day; ash plumes drifted SE, extending as far as 400 km by around 1445. A short eruptive pulse was recorded during 1526-1726, and then afterwards ash plumes rose to below 3 km (10,000 ft) a.s.l. Low-altitude ash emissions on 22 November drifted 100 km S. Minor ashfall was reported in Perryville. AVO lowered the Aviation Color Code and Volcano Alert Level to Orange and Watch, respectively, because of decreased ash emissions. Elevated thermal anomalies were identified in satellite data overnight, and incandescence was visible from a Perryville webcam, suggesting continuing lava effusion which had been obscured by the increased period of ash emissions. Lava effusion was persistent through 27 November.

Geological Summary. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Source: US Geological Survey Alaska Volcano Observatory (AVO)