Weak shallow seismicity that accompanies growth of the crater dome and associated small explosions decreased in the second half of April from an average of 21 events/day to 4 events/day. This seismic activity continued through mid-May at a rate of 2-8 weak earthquakes/day. Average duration of volcanic tremor decreased from 4 hours/day in mid-April to less than 1 hour/day in early May. Fumarolic activity was observed on 25 April, and in May consisted of steam-and-gas plumes rising to 300-1,000 m above the extrusive dome. Seismic data indicated a small explosion on 8 May when the volcano was obscured by clouds.

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: V. Kirianov, IVGG.