Bezymianny is one of the most active volcanoes in Kamchatka and the world. The intensification of its activity began in December 2016 after four years of silence during 2012–2016. There were three paroxysmal explosive volcanic eruptions in 2017; the paper is devoted to the event on December 20 with ash removal up to 15 km above sea level. We describe the course of the eruption and the results of its analysis, including an animated image of the motion of the ash cloud from the volcano, performed on a series of images of Himawari-8 (http://dvrcpod.planeta.smislab.ru/animation/1513757110.gif), with overlaid on it results of modeling the distribution of this ash cloud (http://dvrcpod.planeta.smislab.ru/animation/1513777733.gif). The eruptive cloud moved northeast of the volcano at an average speed of 100 km/h, the main area covered by ash clouds was about 78 000 km2, including 42 600 km2 on land. Ash clouds after the eruption were recorded in the atmosphere at a distance of 1500–2000 km to the northeast of the volcano until December 22, 2017. In addition to ash deposits, as a result of the eruption, deposits of pyroclastic flows (with run out to 5–6 km from the volcano) and mud streams (about 18 km) were formed in Vostochnaya Valley and Sukhaya Khapitsa River. Satellite monitoring of the volcano and analysis of the eruption data was carried out using information systems VolSatView and Signal.

24 декабря 2006 г. произошло эксплозивное извержение вулкана Безымянный. Изучено распределение отложений пеплопада на территории полуострова. Исследованы химический, минеральный, гранулометрический составы тефры, ее водорастворимый комплекс. На площади более 8000 км2 в окружающую среду вместе с 7 млн т пепла поступило около 30 тыс. т водорастворимых веществ. Приведены сведения об извержении из различных источников и выполнена оценка его геологического эффекта. Общий объем изверженной пирокластики составил 0.01–0.014 км3: пепла – 0.004 км3, отложений пирокластического потока – 0.006–0.01 км3.

Close cooperation between researchers at the Alaska Volcano Observatory, USA, the Institute of Volcanic Ge-ology and Geochemistry, Far East Division, Russian Academy of Sciences, and the Kamchatkan Experimental and Methodical Seismological Department, Geophysical Service, Russian Academy of Sciences within the framework of the aviation flight safety program carried out by KVERT (the Kamchatkan Volcanic Eruption Response Team) resulted in a successful forecast of the Bezymianny eruption, all organizations concerned be-ing warned before the event. We describe the precursory phase and evolution of this explosive eruption, as well as its products. The explosive phase lasted one day, the effusive one during about a month. The eruption pro-duced a block and ash pyroclastic flow of merapi type on the volcano's slope and a viscous lava flow on the slope of its dome. The Volcanic Explosivity Index (VEI) is about 2.

The study presents the results of field observations, granulometric and seismoacustic investigations related to a small eruption of the Bezymianny volcano. The characteristic features of the eruption illustrated in the scheme are interpreted to be due to the deeper position in the volcanic channel of the zone enriched in the gas phase.