Recent activity at Karymsky has consisted of ash explosions on 4 June and 20 September 2017, separated by a period of relative quiet (BGVN 42:11). The volcano was quiet after 20 September until another ash explosion on 4 December 2017. This report covers activity from 1 December 2017 through March 2018, using information compiled from the Kamchatka Volcanic Eruptions Response Team (KVERT) and the Tokyo Volcanic Ash Advisory Center (VAAC). According to KVERT, an explosion on 27 January 2018 was last through at least 31 March.

Based on satellite data, KVERT reported that an explosion began at about 0630 on 4 December 2017 and generated an ash cloud that rose to an altitude of 2.7 km and drifted 200 km E. An ash cloud 16 x 12 km in dimension was identified in satellite images about three hours after the explosion, 92 km E of the volcano. The Aviation Color Code was raised from Green to Orange (the second highest level on a four-color scale). A thermal anomaly was identified in satellite data during 3 and 5-6 December.

According to KVERT, another ash plume was identified in satellite data drifting 114 km ENE on 14 December. No further ash emissions were noted afterward; the Aviation Color Code was thus lowered on 24 December to Yellow.

A small ash cloud was identified in satellite imagery drifting near Karymsky on 18 January 2018, and a thermal anomaly was identified on 19 and 23 January. Gas-and-steam plumes drifted 30 km NE and NW on 21 and 25 January, and an ash plume drifted about 100 km NE on 23 January. An explosion at 1430 on 27 January generated ash plumes that rose to an altitude of 5.2 km and drifted 80 km NE-NNE, prompting KVERT to raise the Aviation Color Code to Orange.

Moderate gas-and-steam emissions continued during February and March. Thermal anomalies were detected in satellite images on 3, 9, and 18 February, and 23-26 March; during other days, the volcano was either quiet or obscured by clouds. The Aviation Color Code remained at Orange through the end of the reporting period.

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.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).