During 10-17 April, Veniaminof showed heightened seismicity with several episodes of volcanic tremor and earthquakes. Seismicity decreased significantly prior to the emission of a gas plume with some ash throughout 18 April. The most vigorous phase occurred at about 1730 on 18 April when the plume rose to ~0.5 km above the crater. At about 1130 on 19 April another period of heightened seismic activity began. Due to the increased activity, Veniaminof was upgraded to Concern Color Code Yellow.

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)