Seismic activity at Karymsky was above background levels during 29 August to 5 September. On 28 and 29 August ~120 shallow earthquakes occurred per day, and ash explosions rose to ~4.7 km a.s.l. The number of shallow earthquakes increased to 180 on 1 September, and then to 230 on 2-3 September. Seismic data indicated that ash-and-gas explosions reached 4.5 km a.s.l. On 30 August spasmodic tremor and a thermal anomaly visible on satellite imagery indicated the formation of a pyroclastic flow. The Concern Color Code at Karymsky was reduced from Orange to Yellow.

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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)