Karymsky's eruptive vigor increased. Although seismicity stood at background levels during the past week and slightly above background levels on 14 April, ten=s of volcanic earthquakes per day began to be registered. Observations made on 16 April suggested the presence of fresh ash deposits extending to the ESE for a distance of over 10 km from the summit. Some data suggested that on 17 April an ash-and-gas plume rose 1,000 m above the crater (to ~2,500 m a.s.l.). These events caused authorities to raise the hazard status from Green to Yellow. A 23 April aviation notice described an apparent ash plume at ~3 km a.s.l. directed S.

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), US Air Force Weather Agency