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.

The different roles of variable mantle sources and intra-crustal differentiation processes at Bakening volcano (Kamchatka) and contemporaneous basaltic monogenetic centers are studied using major and trace elements and isotopic data.

Three suites of volcanic activity are recognized: (1) plateau basalts of Lower Pleistocene age; (2) andesites and dacites of the Bakening volcano, the New Bakening volcano dacitic centers nearby; and (3) contemporaneous basaltic cinder cones erupted along subduction zone—parallel N–S faults. Age-data show that the last eruptions in the Bakening area occurred only 600–1200 years ago, suggesting the volcano is potentially active.

Major element variations and petrographic observations provides evidence for a fractionation assemblage of olivine, clinopyroxene, ±plagioclase, ±magnetite (?) within the basaltic suite. The fractionation in the andesites and dacites is dominated by amphibole, clinopyroxene, orthopyroxene and plagioclase plus minor amounts of magnetite and apatite. The youngest cpx-opx-andesites of Bakening main volcano deviate from that trend. Their source was probably formed by mixing of basaltic magmas into the silicic magma chamber of the Bakening volcano. Overall trace element patterns as well as the Sr–Nd–Pb isotopic compositions are quite similar in all rocks despite large differences in their chemical composition (from basalt to rhyodacite). In detail however, the andesite–dacites of the central Bakening volcano show a stronger enrichment in the more incompatible elements and depletion in HREE compared to the monogenetic basaltic centers. This results in a crossing of the REE-pattern for the two suites. The decrease in the HREEs can be explained by amphibole fractionation. A slab component is less likely because it would result in fractionation of the HREE from each other, which is not observed. The higher relative amounts of LILE in the dacitic and the large scatter in the basaltic rocks must be the result of a variable source enrichment by slab-derived fluids overprinting a variable depleted mantle wedge. The plateau basalts are less depleted in HFSE and show a more fractionated HREE pattern. These lavas could either result from a slab component or the addition of an OIB-type enriched mantle in their source.

Oxygen isotope ratios of olivine and clinopyroxene phenocrysts from the Kluchevskoy volcano in Kamchatka have been studied by CO2 and ArF laser techniques. Measured δ18O values of 5.8–7.1‰ for olivine and 6.2–7.5‰ for clinopyroxene are significantly heavier than typical mantle values and cannot be explained by crustal assimilation or a contribution of oceanic sediments. Positive correlations between δ18O and fluid-mobile elements (Cs, Li, Sr, Rb, Ba, Th, U, LREE, K) and a lack of correlation with fluid-immobile elements (HFSE, HREE) suggest that 18O was introduced into the mantle source by a fluid from subducted altered oceanic basalt. This conclusion is supported by radiogenic isotopes (Sr, Nd, Pb). Mass balance excludes simple fluid-induced mantle melting. Instead, our observations are consistent with melting a mantle wedge which has been hydrated by 18O-rich fluids percolating through the mantle wedge. 18O-enriched fluids are derived from the subducted oceanic crust and the Emperor seamount chain, which is responsible for a particularly high fluid flux. This hydrated mantle wedge was subsequently involved in arc magmatism beneath Kluchevskoy by active intra-arc rifting.

A subaqueous eruption in Karymsky lake in the Academii Nauk caldera dramatically changed its water column structure, water chemistry and biological system in less than 24 h, sending major floodwaves down the discharging river and eruption plumes with ash and gases high into the atmosphere. Prior to the eruption, the lake had a pH of about 7, was dominated by bicarbonate, and well stocked with fish, but turned in early 1996 into a stratified, initially steaming waterbody, dominated by sulfate with high Na and K levels, and devoid of fish. Blockage of the outlet led to rising waterlevels, followed by dam breakage and catastrophic water discharge. The total energy input during the eruption is estimated at about 1016 J. The stable isotope composition of the lake water remained dominated by the meteoric meltwaters after the eruption.