No ash or lava emission from Veniaminof was observed during the summer. USGS personnel saw a vapor cloud, which contained no visible ash, emerging from the intra-caldera cone during an overflight on 15 June. They saw vapor plumes rising above the volcano several times during June from observation points 20-60 km SE to SSW of the volcano.

During USGS fieldwork in the caldera 13-14 August, vapor clouds rose from the top and the base of the new cone in the summit crater of the intra-caldera cone. The lava delta in the ice pit was still quite warm and steam rose from it. A repetitive cycle of "vent clearing" was heard; about 15 minutes of a roaring noise like a jet engine was followed by about 20 minutes of quiet, then the roaring resumed. Vapor emission did not appear to increase during the roaring period, but the observers did not have a good view of the cloud. Felt earthquakes occurred during both the roaring and quiet periods. USGS personnel placed control points for aerial photography and sampled material extruded during the 1983-4 eruption.

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.

Information Contacts: T. Miller and M. E. Yount, USGS, Anchorage.