per presents radiocarbon data obtained at the Institute of Volcanology and Institute of Geology, USSR Academy of Sciences , from 77 samples of carbon, wood, and burried soil taken during tephrochronological investigations of soil-pyroclastic covers at the foot of Karymskii and Malyi Semyachek Volcanoes. The authors show the tables of radiocarbon data indicating the main events of the volcanoes as well as the sections showing the position of the dated samples. The accuracy of the radiocarbon dating is discussed. The diagram of soil-pyroclastic cover at the foot of Malyi Semyachek is considered to be as standard for East Kamchatka volcanic zone. Palyno-logical complexes are distinguished; they are dated and adjusted to perioda according to Blitt-Sernander scale.

This study describes the history of formation of Karymskii Volcano from the moment of its emergence. The age of volcano and the caldera where it is located was determined as 6100 (5300 14C) years and 7700 14C years, respectively. Dynamics of the volcano's activity was reconstructed according to absolute chronological scale. Duration of the periods of higher volcanic activity and repose was determined. Large eruptions were dated. Fluctuations in intensity of evacuation of material along with variations in composition of volcanic products were estimated. It has been shown that recent increase in activity started 500 years ago. Analysis of reconstructed dynamics of activity indicated that it would continue not less than 200 years. The character of eruptions is supposed to be close to the recent one.

Восстановлена история формирования вулкана. Динамика его активности реконст­руирована в соответствии с абсолютной хронологической шкалой. Показано, что вулка­ническая активность имела пульсационный характер. Каждый период активизации ха­рактеризуется закономерной сменой состава вулканитов. Возраст собственно стратовулкана Безымянный составил около 5500 лет. Датированы крупнейшие пирокластические извержения. Подсчитан объем продуктов и средняя интенсивность выноса вещества за время жизни вулкана. Отмечено резкое возрастание интенсивности выноса вещества на современном этапе. Анализ реконструированной истории вулкана позволяет полагать, что его активность сохранится в ближайшие 200—300 лет.

The largest Plinian eruption of our era and the latest caldera-forming eruption in the Kurile-Kamchatka region occurred 1700-1800 14C yr BP from the Ksudach volcano. This catastrophic explosive eruption is similar in type and characteristics to the 1883 Krakatau eruption. The volume of pyroclastics ejected was 18-19 km3, including 15 km3 of tephra and 3-4 km of pyroclastic flows. The eruptive column reached 23 km height. A collapse caldera was 4 X 6,5 km in size with a cavity volume of 6.5-7 km3. Tephra was deposited to the north of the volcano to a distance of more than 1000 km. Pyroclastic flows accompanied by ash cloud pyroclastic surges were as long as 20 km. The eruption was first phreatomagmatic, then it became rhythmic, and each rhythm began with the pumiceous tephra eruption followed by the pyroclastic flow formation. Erupted products were rhyolite-dacite remaining invariable during the whole eruption. At the post-caldera stage when the Shtyubel cone started to form within the caldera the basaltic-andesite material began to come to the surface. The driving mechanism of the onset of the eruption is suggested to be an intrusion of magma of basic composition and its mixing with acid magma from a previously existed chamber. The eruption had substantial environmental impact and may have produced a large acidity peak in the Greenland glacial shield.