"Until 1980, only fumarolic activity was observed in the crater formed during the catastrophic eruption of 12 November 1964. An extrusive andesitic dome grew during 1980-81, but its extrusion was not accompanied by notable explosive activity. The dome volume is estimated at 0.021 km³. Subsequently, until 1984, only fumarolic activity continued on the dome. A period of phreatic explosive activity started in 1984, with 7, 4, and 15 explosions in 1984, 1985, and 1986 respectively. In 1987, the frequency of explosions increased to 2-5/month. The explosions were of differing magnitudes, with the most violent ejecting plumes as much as 5 km high. Annular base surges sometimes formed. The explosions apparently created funnel-shaped craters near the dome's summit, with maximum diameters of a few tens of meters. Several of these features merged to form an 80-m-diameter crater on the top of the dome. Episodes of spasmodic volcanic tremor as much as 1 hour long accompanied the explosions, which were continuing in 1988.

"The products of the explosions were mostly ash and sand-sized tephra of andesitic composition. The morphology of the particles indicates that they were formed by crushing of crystallized magma. Products from the explosions outside of the dome seem to be somewhat more basic and finer grained than those originating from the dome."

Geological Summary. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: G. Bogoyavlenskaya and A.B. Belousov, IV.