Large explosive eruptions of volcanoes pose the highest hazard to modern jet f lights, because such eruptions can eject as much as several cubic kilometers of volcanic ash and aerosol into the atmosphere during a few hours or days. The year 2016 saw eruptions on 5 of the 30 active Kamchatka volcanoes (Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Zhupanovsky) and on 3 of the 6 active volcanoes that exist on the North Kuril Islands (Alaid, Ebeko, and Chikurachki). Effusive activity was observed on Sheveluch, Klyuchevskoy, Bezymianny, and Alaid. All volcanoes showed explosive activity. The large explosive events mostly occurred from September through December (Sheveluch), a moderate ash emission accompanied the entire Klyuchevskoy eruption in March–November, and explosive activity of Karymsky, Zhupanovsky, Alaid, and Chikurachki was mostly observed in the earlie r half of the year. The ash ejected in 2016 covered a total area of 600 000 km2, with 460 000 km2 of this being due to Kamchatka volcanoes and 140 000 km2 to the eruptions of the North Kuril volcanoes. The activity of Sheveluch, Klyuchevskoy, and Zhupanovsky was dangerous to international and local f lights, because the explosions sent ash to heights of 10–12 km above sea level, while the eruptions of Bezymianny, Karymsky, Alaid, Ebeko, and Chikurachki were dangerous for local flights, since the ash did not rise higher than 5 km above sea level.

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.

Water plays an extremely important role in volcanism: it acts as an evacuator of viscous melts in a variety of ways, which is ensured by the presence of relevant properties of its phase states, which successively changing with the fall of the environmental parameters. In this sense, the supercritical (fluid) state of water is especially significant. The paper provides a summary of fluid properties that are unique in many ways. The properties determine the relationship between water fluid and silicate melt, which in turn explains the cause of volcanic phenomena and the course of eruptions: explosions of different power, the emergence of the so-called fluidized mass, scorching clouds, landslides and breakthroughs on the slopes, the formation of ignimbrites, as well as the mechanism of gas transport to the foot of volcanoes. Both by role and quantity, water is the main volcanic substance, which together with the silicate melt constitutes magma.

The article presents the results of integrated geologic-geophysical investigation of the Arkhangelsky submarine volcanic massif, which is located in the Bussol Strait in the central zone of the Kurile Island Arc. The massif consists of amalgamated and eroded volcanic edifices and is built up of endogenous basalts and exogenous tuffs. Rocks and minerals to the exclusion of quartz are hydrothermally altered; moreover they were altered after the formation of tuff. High values of the natural remnant magnetization of dredged rocks are caused by the high content of single-domain and pseudo-single-domain grains of titanomagnetite and magnetite. The Arkhangelsky massif most likely was formed during periods of global geomagnetic disturbances. The authors have revealed feeders of the near-vertical and southeastern trends and causative magnetic blocks with different geometric and magnetic characteristics in the edifice of the massif. A peripheral magma chamber has been revealed between depths of 1100–1200 m. At the southeast foot of the massif we found large landslide blocks.