Weak shallow seismicity and tremor increased during late May and early June. For the week ending 27 May, 4-6 earthquakes/day were registered beneath the volcano and the average duration of volcanic tremor was less than 1 hour/day. By 1 June, the range had increased to 3-11 earthquakes/day with 0.4-1.5 hours of tremor/day; 47 events were registered on 30 May. As of 9 June, weak shallow seismicity had reached a rate of 6-29 events/day and tremor was being registered for 2 hours/day. During 2-25 June, weak shallow seismic activity was fairly consistent at 5-30 events/day, with an average volcanic tremor duration of less than 1-2 hours/day. Seismicity decreased in late June to 1-5 events/day with less than 0.5 hours/day of volcanic tremor. In early July, seismicity decreased to 2-3 events/day; tremor was unchanged.

Weak fumarolic activity generated steam-and-gas plumes 300-400 m above the extrusive dome. This activity increased significantly after a tectonic earthquake at 0530 on 8 June, with a plume rising up to 2 km. The plume rose 1-1.5 km above the extrusive dome from 10 June to 7 July, and originated from two different vents during at least part of this period. On 7 July two gas-and-ash bursts were observed, one at 0955 rising up to 5 km above the crater, and the other at 1550 rising up to 3 km; both clouds drifted NW.

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.