KVERT reported that during 18-25 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 5.2 km (17,100 ft) a.s.l. According to video camera data and visual observations, ash plumes rose to an altitude of 5.5 km (18,000 ft) a.s.l. on 18, 19, and 22 September, and hot avalanches from the lava dome were noted during 18 and 22-23 September. Ash plumes were occasionally seen drifting 15-70 km N, NW, and SE. The Level of Aviation Color Code remained at Orange.

Based on information from KEMSD, the Tokyo VAAC reported that on 28 September an eruption produced a plume that rose to an altitude of 7 km (23,000 ft) a.s.l.

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.

Sources: Kamchatkan Volcanic Eruption Response Team (KVERT), Tokyo Volcanic Ash Advisory Center (VAAC)