A new approach to definition of the term "active volcano" has been worked out on the basis of detailed reconstruction of the eruptive activity of Kamchatka volcanoes. We suggest to consider active those poligenous volcanoes whose at least a single eruption has been ascertained and dated over the last 3000-3500. Two sub-groups of active volcanoes have been distinguished: sub-group of active volcanoes with data available on the historically documented eruptions or fumarolic activity and the one of potentially active volcanoes without such data but whose eruptions have been revealed over the last 3500 years. Using similar criteria the potentially active fields of the areal basalt volcanism, regional zones of cinder cones and concentrated manifestation of the multivent extrusive volcanism are also distinguished. We propose to use data obtained for the new catalogue of active Kamchatka volcanoes and for the long-term prediction of volcanic activity and associated hazard.

Data of seismological, gravimetric and electromagnetic study are presented. Main peculiarities of deep-seated structure of the earth's crust and upper mantle to the depth of ~90 km have been revealed. Margins of the lithosphere blocks on ground and water area of the Avacha bay have been established. A complex geologic-geophysical model beneath Avachinsky volcano has been developed. It involves crustal magmatic chamber at depth 15 to 25 km, intrusion overlying it, peripheric chamber at depth ~0 to 2 km, and zone saturated with liquid fluids in Avachinsky graben. Major geodynamic processes, which have been operating in the earth's crust at present, are considered. An important role is given to the crustal permeable zone containing fluids. Recommendations are made for the deep well-drilling in the area of Avachinsky volcano with the aim of searching for geothermal deposits.

Проведены исследования газового состава и изотопного отношения гелия и 4He/20Ne гидротерм в пределах Карымского вулканического центра и характера их изменений в связи с активизацией тек-тоно-магматической обстановки в этом регионе, проявившейся в конце 1995 г. и в начале 1996 г. в виде серии сильных землетрясений, извержения Карымского вулкана и мощного подводного извержения, эпицентр которого располагался в Карымском озере. Опробованы как ранее существовавшие здесь источники Карымские и Академии Наук, так и вновь образовавшиеся гидротермы и фумарола в районе подводного извержения. Совместно в этим изучен состав растворенных газов оз. Карымское

Дано описание и представлены первые результаты изучения начальной стадии извержения вулкана Шивелуч в мае-июле 2001 г. Происходили рои землетрясений, образование трех новых больших андезитов лавовых куполов, крупные взрывы и другие связанные явления. Приведены сведения о проявлениях активности вулкана в предшествующий извержению период. Представлены результаты визуальных и сейсмологических наблюдений, проведенных во время подготовки извержения и его начальной стадии, результаты изучения динамики извержения по данным аэрофотосъемки и геодезических наблюдений, данные обследования пирокластических и грязевых потоков, наблюдавшихся во время начальной стадии извержения.

Direct experiments on high-temperature (910 and 620°C) fumaroles of Kudryavy Volcano have demonstrated that low-density volcanic gas interacts with rock-forming and ore minerals (12 minerals were studied). The mechanism of the interaction is determined by gas metasomatism reactions: (a) at given conditions, sphalerite, calcite, barite, and gypsum are either dissolved and removed by gas or replaced with other minerals (calcite → anhydrite); (b) reactions with silicates (feldspars, olivine, and biotite) proceed owing to diffusion cation exchange. Structural rearrangements in biotite are possible due to dehydration and loss of alkalis and aluminum. The kinetics of interaction between hot gas and silicates is governed by the rate of cation diffusion in the mineral at given conditions. Precipitation of sublimates on the surfaces of minerals does not affect much the process of reactions. Interaction between volcanic gas and minerals results in albitization of feldspars and ferruginization of olivine and biotite. The scale of metasomatism in the crystalline rocks of Kudryavyi Volcano has been estimated as about 3 mm in 115 years.