AVO reported that during 13-15 August seismic tremor at Veniaminof was high, and persistent elevated surface temperatures consistent with lava effusion were visible on satellite imagery. During 16-17 August the high levels of tremor became sustained; seismicity remained high through 20 August. Very high surface temperatures were detected in images during 16-17 August; only weak thermal signals were evident through the cloud cover in satellite data during 17-18 August. Clear views on 18 August from the FAA web-camera in Perryville (32 km SSE) showed minor ash emissions. During a helicopter overflight on 19 August geologists observed two active lava flows from the cone, and lava flowing passively over ice at the foot of the cone. Elevated surface temperatures were detected in satellite data during 19-20 August. Clear web-camera views showed minor ash emissions rising to an altitude of 3.7 (12,000 ft) a.s.l. and drifting W and then SSE, just past 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)