The geochemical variations of magmas across and along supra-subduction zones (SSZ) have been commonly attributed to profound changes in the phase and chemical compositions of the mantle source and subduction-derived melt and fluid fluxes, as well as the physical parameters (e.g. depth, temperature, oxygen fugacity etc) of slab dehydration, mineral breakdown and melting. Here we test the variability of the Late Quaternary primitive magmas in the southern and northern parts of the meridionally oriented Eastern Volcanic Belt (EVB) of Kamchatka, with a slab depth varying from 60 to 160 km. Eight high-Mg (Mg# > 60 mol%) basalts were characterized for major, trace and platinum-group element (PGE) abundances, as well as the compositions of olivine phenocrysts and olivine-hosted spinel inclusions. The basalts in our study are geochemically typical of SSZ magmas and contain similar liquidus assemblages of forsteritic olivine (Mg# 78–92 mol%), low-Ti Cr-spinel and clinopyroxene. Although the absolute abundances of major and trace elements, and their ratios, in the basalts fluctuate to some extent, the observed variability cannot be correlated with any of considered parameters in the geometry of the Kamchatka SSZ and conditions of melting. This unexpected result led to the evaluation of the platinum-group element (PGE) systematics against the lithophile and chalcophile trace element geochemistry and the compositions of phenocrysts. Total whole-rock PGE content varies from 2.3 to 11.7 ppb, whereas the normalized PGE concentration patterns are typical for supra-subduction zones magmas and broadly similar in all studied samples. They are enriched in Rh, Pd and Pt relative to mid-ocean ridge basalts (MORB) and have nearly identical concentrations of Ir-group PGE. The only parameter that correlates well with PGE contents is the average Mg# of olivine phenocrysts from 84 to 90.3 mol%. This is interpreted to result from minor cryptic fractionation of sulfide melt, together with primitive olivine, in low-to-mid crustal conditions. Negative Ru anomalies on chondrite-normalized diagrams correspond to the Fe2+/Fe3+ ratios in spinel (a proxy for magma redox conditions), which reflects a replacement of monosulfide solid solution by laurite in the mantle wedge during oxidation.

The powerful explosive eruptions with large volumes of volcanic ash pose a great danger to the population and jet aircraft. Global experience in monitoring volcanoes and observing changes in the parameters of their thermal anomalies is successfully used to analyze the activity of volcanoes and predict their danger to the population. The Kamchatka Peninsula in Russia, with its 30 active volcanoes, is one of the most volcanically active regions in the world. The article considers the thermal activity in 2015–2022 of the Klyuchevskoy, Sheveluch, Bezymianny, and Karymsky volcanoes, whose rock composition varies from basaltic andesite to dacite. This study is based on the analysis of the Value of Temperature Difference between the thermal Anomaly and the Background (the VTDAB), obtained by manual processing of the AVHRR, MODIS, VIIRS, and MSU-MR satellite data in the VolSatView information system. Based on the VTDAB data, the following “background activity of the volcanoes” was determined: 20 °C for Sheveluch and Bezymianny, 12 °C for Klyuchevskoy, and 13–15 °C for Karymsky. This study showed that the highest temperature of the thermal anomaly corresponds to the juvenile magmatic material that arrived on the earth’s surface. The highest VTDAB is different for each volcano; it depends on the composition of the eruptive products produced by the volcano and on the character of an eruption. A joint analysis of the dynamics of the eruption of each volcano and changes in its thermal activity made it possible to determine the range of the VTDAB for different phases of a volcanic eruption.

Constant observations of the eruption process of Bezymianny volcano and an incessant control of the properties and volume of ejected products enabled us to reconstruct cristallization conditions of the magma in the top parts of the volcanic vent assumedly to a depth of 6–8 km.
Substantial changes in the mineralogy and petrography of lavas have been recorded during the thirteen years of the activity of the volcano.
Hornblende andesites of the first portions of eruptions were replaced by bipyroxene andesites, in which the second generation of phenocrysts had appeared — subphenocrysts. The content of subphenocrysts was progressively increasing with a simultaneous drop in the amount of glass to nearly one half of the former amount.
In the process of eruption the chemical composition of rocks did not change: a high viscosity of the melt prevented a differentiation in the upper parts of the magmatic column.
A relative permanence of the composition and amount of phenocrysts of plagioclase and pyroxene throughout all the eruption stages indicates that already at a depth of 7–8 km the melt contains intratelluric phenocrysts.
The appearance in lavas of the last eruption stage of phenocrysts belonging to the 2nd generation despite an unchanged chemical composition, indicates their cristallization in subsurface conditions in the interval of 5–10 years.

На основе результатов маршрутных обследований 2020–2022 гг. в работе представлена характеристика особенностей геологического строения и валового состава пород вулкана Кроноцкого – одного из наименее изученных эруптивных центров Восточного вулканического пояса (ВВП) Камчатки. Объем постройки стратовулкана оценен в 350 км3, что существенно превышает объемы других стратовулканов фронтальной зоны ВВП. Породы вулкана представлены низко-K, высоко-Fe толеитовыми базальтами и андезибазальтами (SiO2 = 47.04‒53.15 мас. %; K2O = 0.24‒0.65 мас. %; FeO*/MgO = 1.2‒2.89). Базальты отличаются крайне низкими содержаниями кремнезема, калия, титана и фосфора по сравнению с породами других фронтальных вулканов Камчатки. Выявленные петрохимические отличия были использованы для уточнения принадлежности объектов, расположенных на стыке сближенных построек вулканов Кроноцкого и Крашенинникова. Полученные данные послужат основой дальнейшей петролого-геохимической характеристики вулкана, а также могут быть использованы для реконструкции последовательности вулканических событий на исследуемой территории, в том числе и для уточнения истории формирования Кроноцкого озера.

One of the most important tasks when studying volcanic activity is to monitor their thermal radiation. To fix and assess the evolution of thermal anomalies in areas of volcanoes, specialized hardware-thermal imagers are usually used, as well as specialized instruments of modern satellite systems. The data obtained with their help contain information that makes it relatively easy to track changes in temperature and the size of a thermal anomaly. At the same time, due to the high cost of such complexes and other limitations, thermal imagers sometimes cannot be used to solve scientific problems related to the study of volcanoes. In the current paper, day/night video cameras with an infrared-cut filter are considered as an alternative to specialized tools for monitoring volcanoes’ thermal activity. In the daytime, a camera operated in the visible range, and at night the filter was removed, increasing the camera’s light sensitivity by allowing near-infrared light to hit the sensor. In that mode, a visible thermal anomaly could be registered on images, as well as other bright glows, flares, and other artifacts. The purpose of this study is to detect thermal anomalies on night images, separate them from other bright areas, and find their characteristics, which could be used for volcano activity monitoring. Using the image archive of the Sheveluch volcano as an example, this article presents the results of developing a computer algorithm that makes it possible to find and classify thermal anomalies on video frames with an accuracy of 98%. The test results are presented, along with their validation based on thermal activity data obtained from satellite systems.