Three-dimensional structural images of the P-wave velocity below the edifice of the great Klyuchevskoy group of volcanoes in central Kamchatka are derived via tomographic inversion. The structures show a distinct low velocity feature extending from around 20 km depth to 35 km depth, indicating evidence of magma ponding near the Moho discontinuity. The extensive low velocity feature represents, at least to some degree, the source of the large volume of magma currently erupting at the surface near the Klyuchevskoy group.

Teleseismic receiver functions (RFs) from a yearlong broadband seismological experiment in Kamchatka reveal regional variations in the Moho, anisotropy in the supra-slab mantle wedge, and, along the eastern coast, Ps converted phases from the steeply dipping slab. We analyze both radial- and transverse-component RFs in bin-averaged epicentral and backazimuthal sweeps, in order to detect Ps moveout and polarity variations diagnostic of interface depth, interface dip, and anisotropic fabric within the shallow mantle and crust. At some stations, the radial RF is overprinted by near-surface resonances, but anisotropic structure can be inferred from the transverse RF. Using forward modeling to match the observed RFs, we find Moho depth to range between 30 and 40 km across the peninsula, with a gradational crust –mantle transition beneath some stations along the eastern coast. Anisotropy beneath the Moho is required to fit the transverse RFs at most stations. Anisotropy in the lower crust is required at a minority of stations. Modeling the amplitude and backazimuthal variation of the Ps waveform suggests that an inclined axis of symmetry and 5 – 10% anisotropy are typical for the crust and the shallow mantle. The apparent symmetry axes of the anisotropic layers are typically trench-normal, but trench-parallel symmetry axes are found for stations APA and ESS, both at the fringes of the central Kamchatka depression. Transverse RFs from east-coast stations KRO, TUM, ZUP and PET are fit well by two anisotropic mantle layers with trench-normal symmetry axes and opposing tilts. Strong anisotropy in the supraslab mantle wedge suggests that the mantle ‘‘lithosphere’’ beneath the Kamchatka volcanic arc is actively deforming, strained either by wedge corner flow at depth or by trenchward suction of crust as the Pacific slab retreats.

Abstract A large dike intrusion and fissure eruption lasting 9 months began on November 27, 2013, beneath the south flank of Tolbachik Volcano, Kamchatka, Russia. The eruption was the most recent at Tolbachik since the Great Tolbachik Eruption from 1975 to 1976. The 2012 eruption was preceded by more than 6 months of seismicity that clustered beneath the east flank of the volcano along a NW–SE trend. Seismicity increased dramatically before the eruption, with propagation of the seismicity from the central volcano conduit in the final hours. We use interferometric synthetic aperture radar (InSAR) to compute relative displacement images (interferograms) for {SAR} data pairs spanning the eruption. We use satellite {SAR} data from the Canadian Space Agency's RADARSAT-2 and from the Italian Space Agency's COSMO-SkyMed missions. Data are modeled first through a Markov Chain Monte Carlo solution for a single tensile dislocation (dike). We then use a boundary element method that includes topography to model a distributed dike-opening model. We find the best-fitting dike dips 80° to the {WNW} with maximum opening of 6–8 m, localized in the near surface and more broadly distributed in distinct regions up to 3 km beneath the surface, which varies from 1 to 2 km elevation for the eruptive fissures. The distribution of dike opening and its correspondence with co-diking seismicity suggests that the dike propagated radially from Tolbachik's central conduit.

На примере двух мощных извержений конуса Квицапу вулкана Сьерро-Ассуль (Чили) рассматривается проблема эффузивных извержений магм с высокими предэруптивными содержаниями летучих. Предложен физико-химический механизм дегазации магм с потерей ими летучих до появления на поверхности. Модель основана на взаимодействии магм, находившихся в разных по глубине очагах, и различии между растворимостью воды в расплаве и ее равновесной концентрацией в протяженном по вертикали магматическом теле. При этом малоглубинный очаг может аккумулировать летучие, выделяющиеся из магмы, поступающей в него из глубинного очага. Дается объяснение резких различий в характере извержений 1846–1847 и 1932 г. при идентичном химико-петрографическом составе магм.

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,