KVERT reported that seismic activity at Karymsky was above background levels during 14-21 September. Observations of satellite imagery revealed that ash plumes drifted SE on 15 September and a thermal anomaly was present in the crater during 13-15 and 17-19 September. Based on seismic interpretation, ash plumes may have risen to an altitude of 3.3 km (10,800 ft) a.s.l. during 15-16 and 20 September. The Level of Concern Color Code remained at Orange.

Based on pilot reports, information from KEMSD, observations of satellite imagery, and observations in the Petropavlovsk-Kamchatsky Flight Information Region (FIR), the Tokyo VAAC reported that ash plumes rose to altitudes of 4.6 km (15,000 ft) a.s.l. on 21 September and 3.4 km (11,000 ft) a.s.l. on 25 September.

Geological Summary. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

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