AVO reported that on 20 August residents of Perryville (32 km SSE) reported hearing loud explosions coming from Veniaminof, and air waves were detected by infrasound equipment in Dillingham (322 km NE). Trace amounts of ash fell in Perryville. During 20-21 August seismic activity at Veniaminof decreased; seismicity became more episodic and fluctuated between periods of relative quiet and short periods of low-level, nearly continuous tremor. Minor ash-and-steam emissions likely continued, but effusion of lava may have slowed down or possibly stopped. Elevated surface temperatures at the cone were observed in satellite data.

Seismicity during 22-26 August remained low; small ash bursts were probably produced during short periods of elevated tremor. During 23-26 August satellite data showed weak thermal anomalies at the intracaldera cone and very minor ash emissions were occasionally observed in web camera views from Perryville. During 26-27 August seismicity was characterized by nearly continuous, gradually fluctuating tremor possibly indicative of low-level ash emission and probable lava effusion. Satellite images detected a thermal signal at the intracaldera cone. Web camera views from Perryville showed a slightly more robust ash plume, extending ESE beyond the caldera rim. The Volcano Alert Level remained at Watch and the Aviation Color code remained at Orange.

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)