This paper reports new FTIR data on the H2O and CO2 concentrations in glasses of 26 naturally quenched and experimentally partially homogenized melt inclusions in olivine (Fo85–91) phenocrysts from rocks of the Kliuchevskoi volcano. Measured H2O concentrations in the inclusions range from 0.02 to 4 wt.%. The wide variations in the H2O content of the inclusions, which do not correlate with the host olivine composition and contents of major elements in the melts, are explained by the H2O escape from inclusions via diffusion through the host olivine during the magma eruption and the following cooling. The largest H2O loss is characteristic of inclusions from lava samples which cooled slowly after eruption. The minimal H2O loss is observed for inclusions from rapidly quenched pyroclastic rocks. Parental magmas of the Kliuchevskoi volcano are estimated to contain 3.5 wt.% H2O. The new data imply a 40 °C lower mantle temperatures than that estimated earlier for the Kliuchevskoi primary melts. The concentrations of CO2 in glasses range from <0.01 to 0.13 wt.% and do not correlate with the type of studied inclusions and their composition. The calculated pressures of melt equilibria with H2O–CO2 fluid inside the inclusions are lower than 270 MPa. They are significantly lower than a pressure of 500 MPa calculated from the density (~0.8 g/cm3) of cogenetic fluid inclusions in high-Fo olivine. The significant pressure drop inside the melt inclusions after their trapping in olivine might be due to the H2O loss and redistribution of CO2 from melt to daughter fluid phase. Compared with melt inclusions, cogenetic fluid inclusions provide independent information about the crystallization pressures of olivine and initial CO2 content in the Kliuchevskoi magma, which were estimated to be at least 500 MPa and 0.35 wt.%, respectively. The maximum CO2 concentrations in the primary Kliuchevskoi melts are estimated at 0.8–0.9 wt.%. The decompression crystallization of the Kliuchevskoi magmas starts at depths of 30–40 km and proceeds with a continuous decrease in CO2 content and an increase (up to 6–7 wt.%) and then a decrease (at <300 MPa) in H2O content in melts, which explains the origin of the whole spectrum of rocks and melt inclusions of the Kliuchevskoi volcano.

Determination of the volcanic eruption source parameters—total grain-size distribution and vertical ash mass distribution (VMD) within the source—is carried out on a collection of measured-area samples and granulometry data. For this, the geophysical inverse methods and Hybrid Particle and Concentration Transport Model (HYPACT) driven by wind and turbulence fields simulated with the Regional Atmospheric Modeling System (RAMS) are used. A two-step inversion procedure is proposed to obtain approximate but physically meaningful solution when the total number of ashfall samples is small and it is not possible to make a good initial guess of the source parameters. First, a spectrum of particle fall velocities is estimated by selecting a best-fit subset of aerodynamically distinct subpopulations of free and aggregate particles from the trial set used to simulate a polycomponent ashfall. The singular value decomposition (SVD) analysis is then employed to identify spatial components of the ash emissions’ vertical distribution, as resolvable by the observations. Model validation experiments are conducted for the January 12, 2011, short-duration vulcanian explosion at Kizimen and paroxysmal phase of the December 24, 2006, sub-Plinian eruption at Bezymianny. The derived VMDs exhibit high variability in fine ash content (~ 60–100 wt%) as well as strong secondary maxima in the lower troposphere, likely reflecting the contribution of ash particles fallen out of co-pyroclastic flow ash clouds and partially collapsing eruption columns.

Data are presented from studies of volcanoes in the Karymsky long-living volcanic center, Kamchatka in 1996. We examine the dynamics and rock composition for eruptions that started simultaneously on Karymsky Volcano and in the Akademia Nauk caldera. The effusive-explosive eruption of Karymsky Volcano was resumed after a 14-year repose period, producing about 30 million tons of andesite-dacite discharges through the summit vent. Long-continued eruptive activity of that volcano is supposed to go on during the near future. Simultaneously with this activity, typical of Karymsky Volcano, a subaquaceous explosive eruption was observed in the lake that occupies the Akademia Nauk caldera 6 km south of the volcano for the first time in Kamchatka during the historical period. An edifice arose in the northern part of Lake Karymsky during 18 hours of this eruption consisting of basaltic and basaltic andesite pyroclastic material surrounding a crater of diameter 650 m. The amount of erupted pyroclastic material is estimated as 0.04 km3, the total weight being over 70 million tons. A discussion is provided of the impact of these eruptions on the environment; we describe renewed hydrothermal activity and the formation of a new group of hot springs in the Akademia Nauk caldera, and estimate the possibility of breakthrough floods from Lake Karymsky etc.

A thermal model has been constructed for a steady-state glacier of Ushkovskii Volcano. Analysis of ice mass balance components has revealed elevated heat flow (mean valce 10 W/m2) in the summit crater wich has remained nearly constant over the last 40 years. The measured accumulation rate and temperature distribution in the snow and firn body in the middle of the Gorshkov crater suggest the existence of a considerable uplift (a small embedded crater) overlain by the glaciers. The formulas proposed in this paper can be used to evaluate critical state parameters for unsteady ice masses on the slopes of Klyuchevskoi Volcano.

Tyatya Volcano, situated in Kunashir Island at the southwestern end of Kuril Islands, is a large composite stratovolcano and one of the most active volcanoes in the Kuril arc. The volcanic edifice can be divided into the old and the young ones, which are composed of rocks of distinct magma types, low‐ and medium‐K series, respectively. The young volcano has a summit caldera with a central cone. Recent eruptions have occurred at the central cone and at the flank vents of the young volcano. We found several distal ash layers at the volcano and identified their ages and sources, that is, tephras of ad 1856, ad 1739, ad 1694 and ca 1 Ka derived from three volcanoes of Hokkaido, Japan, and caad 969 from Baitoushan Volcano of China/North Korea. These could provide good time markers to reveal the eruptive history of the central cone, which had continued intermittently with Strombolian eruptions and lava flow effusions since before 1 Ka. Relatively explosive eruptions have occurred three times at the cone during the past 1000 years. We revealed that, topographically, the youngest lava flows from the cone are covered not by the tephra of ad 1739 but by that of ad 1856. This evidence, together with a report of dense smoke rising from the summit in ad 1812, suggests that the latest major eruption with lava effusion from the central cone occurred in this year. In 1973, after a long period of dormancy, short‐lived phreatomagmatic eruptions began to occur from fissure vents at the northern flank of the young volcano. This was followed by large eruptions of Strombolian to sub‐Plinian types occurring from several craters at the southern flank. The 1973 activity is evaluated as Volcanic Explosivity Index = 4 (approximately 0.2 km3), the largest eruption during the 20th century in the southwestern Kuril arc. The rocks of the central cone are strongly porphyritic basalt and basaltic andesite, whereas the 1973 scoria is aphyric basalt, suggesting that magma feeding systems are definitely different between the summit and flank eruptions.