Report on Sheveluch (Russia) — 14 August-20 August 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 August-20 August 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Sheveluch (Russia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 14 August-20 August 2002. Smithsonian Institution and US Geological Survey.
56.653°N, 161.36°E; summit elev. 3283 m
All times are local (unless otherwise noted)
During 9-16 August, seismicity remained above background levels at Shiveluch with about 10 earthquakes occurring with magnitudes 1.7-2.4 and a number of smaller earthquakes at depths of 0-6 km. In addition, many other local shallow seismic signals were registered, which possibly indicated ash-and-gas explosions (one to three per day to heights of 1.5-2.5 km above the dome). Avalanches were also registered. Seismicity decreased slightly by the end of the week. On several days thermal anomalies were visible on satellite imagery. The Concern Color Code was reduced from Orange ("explosive eruption is possible within a few days and may occur with little or no warning") to Yellow ("volcano is restless").
Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. 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 dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. 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.