Following a week of cloudiness, the gas-and-steam plume . . . was seen on 13 August rising . . . 800 m above the crater. The volcano was again obscured by clouds 14-19 August. When observed on 20 August, the gas-and-steam plume was as high as 1.5 km above the crater and was carried S about 5 km. On 9 September, the plume reached a height of 800 m above the crater and drifted S to a distance of 40 km.

The SE part of the extrusive dome continued to grow from 2-9 September. During that time, the relative height of the dome increased from 370-380 m to 450-470 m, while the upper diameter increased from 300 to 400 m, and the lower diameter increased from 500 to 600 m. Extrusive spines also appeared on the SE sector of the dome, and the frequency of explosions increased to one every 10-15 minutes. Explosive activity was not restricted to any one area of the dome.

Seismicity decreased throughout August before increasing in September to a level similar to 6 April, two weeks before the last eruption. Continuous volcanic tremor was recorded in both periods. Based on previous eruption patterns, an increase in seismicity above the current levels may precede an explosive eruption that could destroy the upper section of the active 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: V. Kirianov, IVGG.