On 18 June AVO stated that periods of seismic tremor and occasional earthquakes had been recorded at Veniaminof over the past few days. The increase above background levels prompted AVO to raise the Volcano Alert Level to Advisory and the Aviation Color Code to Yellow. Periods of low-amplitude seismic tremor decreased in frequency during 19-20 June, and were not detected at all by 21 June.

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)