KVERT reported that during 4-11 September seismic activity from Shiveluch was above background levels. Analyses of satellite imagery revealed a large daily thermal anomaly over the lava dome. Based on interpretations of seismic data, ash plumes possibly rose to an altitude of 4.2 km (13,800 ft) a.s.l. and hot avalanches occurred at the lava dome. Gas-and-steam plumes rose to an altitude of 4 km (13,100 ft) a.s.l. during 4-9 September. An ash plume was seen in satellite imagery drifting 80 km E on 8 September.

On 11 September, KVERT reported strong explosions. Based on interpretations of seismic data, ash plumes rose to an altitude greater than 15 km (49,200 ft) a.s.l. The seismic network then detected eight minutes of pyroclastic flows from the lava dome; resulting plumes rose to an altitude of approximately 10 km (32,800 ft) a.s.l. The Aviation Color Code level was raised to Red. Ten more events characterized as ash explosions and either pyroclastic flows or avalanches were detected. Cloud cover prevented visual observations. Seismicity decreased during 11-12 September, and indicated that ash plumes rose to altitudes of 4.5-6.5 km (14,800-21,300 ft) a.s.l. The Aviation Color Code level was lowered to Orange.

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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)