На основании палинологических исследований приводится возрастное расчленение вулканогенно-осадочных отложений Узон-Гейзерной кальдерной депрессии и палеогеографическая обстановка времени осадконакопления. Установлен позднеплейстоцен-голоценовый возраст отложений. Датированы основные события посткальдерной вулканической деятельности в кальдере Узон.

The old views on the style of the Avachinsky eruptions during 1737- 1909 have partially been revised based on new data obtained by the authors. We specified their types and geological-geomorphological effect and made an assessment of the related volcanic hazards. All the eruptions were merely explosive except for the effusive-explosive eruption of 1894-1895. The eruptions of 1737, 1779 and 1827 are referred to large for this historical eruptive stage, the rest (of 1772, 1851-1855, 1878, 1881, 1894-1895 and 1909) are regarded as small and moderate.

The eruptive history of Ebeko since its arising about 2400 years ago to the beginning of the 17th century was reconstructed based on data of special geological, gecmorphological, tephrochronological researches using the 14С dating (more than 20 dates). Six stages of increased activity with the duration of 200-300 years were recognized. These stages are divided by quiet periods of the same duration. It is shown that the eruption of juvenile material (lava and pyroclastic) took place only at the first stage (420-200 years before our era). All the next eruptions were phreatic, but of different power. Large-scale maps and lopoplans of the Ebeko volcanic group (Ebeko, Neozhidanhy, Nezametny) with the nearest areas were compiled and the present-day morphology of the Ebeko summit part was described m detail based on ariborne materials of 1987, 1988, 1990. It is presented that, not considering the first eruptive stage, the main volcanic hazard for the Ebeco region and the town of Severo-Kurilsk situated near the volcano came from the moving of large lahars and tephra fall.

Consequences of the Ebeko eruptions in 17-20 centuries were reconstructured in detail based on history information and data of tephrochronoSogical investigations and air photography of 1960, 1987, 1988, 1990. It is shown that all the eruptions were phreatic and conditionally phreatomagmatic with thermal alimentation as a very heated dike-sill complex with volume of more than 1 km , in the zone of extension NNW (Az. 25°), where volcanoes of the Vernadsky ridge are located (Paramushir island). It is supposed that the main future hazard for the Severo-Kurilsk town and the nearest areas is expecting from the moving of lahars of large-volume along the Kuzminka and the Matrosskaya rivers originated from the Ebeko volcano. Lesser hazard is expecting from ashfalls produced by the Ebeko and other volcanoes of the North Kuril and the Souih Kamchatka. It is proved that a big hazard for the may arise from the future eruption of the Ebeko similar to those eruptions of 1934-1935. It is recommended some ways for defence of the town.

Mechanism of activity of the giant basaltic Klyuchevskoy volcano is stadied. Magma overpressure in its feeding system, surrounding rocks heating, amount and concentration of numerous radial dykes beneath the volcano at distances up to 20 km are calculated. It is shown that basaltic magmas of the Klyushevskoy volcano should be formed during their ascent through the crust and have to be accumulated in it. Results are compared with data on volcano eruptions, on the structure of the crust and earthquakes beneath the volcano. The state of the volcano and its unstable upper cone, and probable features of its next large eruptions are estimated.

As a result of detailed mineralogical and petrochemical research of calc-alcaline magnesial basalts produced by 21 explosive and effusive lateral break-outs of Kliuchevskoy volcano and based on the data of geochcmical thermometry new data obtained on the chemical composition of magnesial basalts, phenocrysts of olivines and clinopyroxenes and condition: of their crystallization in intermediate magmatic chambers. Balance calculations show that magnesial basalts are products of initial high maghesial magmas.

This paper presents the results of visual observations, particle-size analysis, seismological observations, and acoustic measurements carried out during a small-magnitude eruption of Bezymyannyi in June 1986. A mlodel is proposed for the mechanism of the eruption. A specific character of the eruption is explained by a deeper localization of a gas-rich aagia portion in the conduit,