Conditions of high-temperature volcano-related mineral formation are a source of the new and rare minerals and their associations; they are rather fragmentarily described for volcanic systems as a whole, except for several objects characterized in this regard. The study aim is to present the first results of the mineralogical study of atypical suprasubduction zone neoformation encountered from the Taketomi flank eruption (1933–1934) of the Alaid volcano (Kuril Islands), which has been studied through electron microprobe analyses and powder and single-crystal X-ray diffraction. The following mineral paragenesis is described: diopside, andradite, anorthite, wollastonite, esseneite, wadalite, rhönite-like mineral, fluorite, calcite, apatite, and atacamite. The parageneses of calcium silicates found in volcanic systems are usually interpreted as reworked crustal xenoliths and commonly associated with volcanoes that have a carbonate basement. However, carbonates have not been previously described at the base of the Alaid volcano. Even though the skarn nature of such a mineral paragenesis is possible, we suggest the important role of high-temperature volcanic gases along with the pyrometamorphic effect in the mineral-forming process at depth or in near-surface conditions (fumarole-like type in the form of a system of cracks and burrows). The described mineral paragenesis has not been previously documented, at least for the North Kuril Islands. A detailed mineralogical study of such formations is one of the important steps in understanding the functioning of magmatic systems, the circulation and transformation of natural matter, and mineral-forming processes.

Sheveluch is one of the most active volcanoes in Kamchatka. Its modern edifice includes three main elements: Old Sheveluch, an ancient caldera and Young Sheveluch. On the southeastern slope of Old Sheveluch, there is a group of ancient extrusive domes (from south to north): Sherokhovataya, Krasnaya, Karan, and Sopochka na sklone. Only in the area of the Karan dome are there heated areas with mofets temperature of 70–96°C. After the powerful explosive eruption of the Sheveluch volcano in April 2023, the gas–steam activity of the Karan dome intensified, and a thermal anomaly began to be noted in satellite images of the area of this dome. On April 26, 2024, in a JPSS‑1 satellite image at 15:07 UTC, Kamchatkan Volcanic Eruption Response Team scientists discovered a bright thermal anomaly in the area of the Karan dome; that is, they recorded a unique phenomenon on this day: the birth of a new volcanogenic formation—the new lava dome. It was given the name 300 Years of the Russian Academy of Sciences. As of June 7, 2024, the size of the new dome was 800 × 500 m and the area of the dome crown was 0.19 km2. The eruption of the new lava dome 300 Years of the Russian Academy of Sciences is continuing.

The crystal–chemical behavior of two layered titanosilicate minerals with porous crystal structures, kupletskite, K2NaMn72+Ti2(Si4O12)2O2(OH)4F, and kupletskite-(Cs), Cs2NaMn72+Ti2(Si4O12)2O2(OH)4F, was investigated under high-temperature conditions using single-crystal and powder X-ray diffraction; infrared and optical absorption spectroscopy and electron-microprobe analysis. Both minerals undergo topotactic transformation to dehydroxylated and oxidized high-temperature (HT) modifications at temperature above 500 °C while maintaining the basic bond topology of the astrophyllite structure-type. The high-temperature structures show contraction of the unit-cell parameters similar to that of Fe2+-dominant astrophyllite, indicating that Mn2+ oxidizes along with Fe2+ in M(2)–M(4) sites. The oxidation of Mn2+ is confirmed by the increase of the Mn3+-related absorption (in optical spectra) that is inversely correlated with the intensity of O–H bands in the infrared spectra. The Fe,Mn-oxidation is also evident by the contraction of the M(2), M(3), and M(4)O6 octahedra. The M(1)–O bond length increases slightly, indicating a preference for mono- and divalent cations to occupy the M(1) site in the heated structure; this may be due to site-selective oxidation and/or migration of unoxidized cations (as previously shown for lobanovite) to this site. The role of extra framework A-site cations (K, Cs) in thermal expansion of these minerals is discussed.

Krenitsyn Peak is one of the two active volcanoes on Onekotan Island (Greater Kuril Ridge). The inaccessibility of the island, along with the volcano being situated within a sizeable (7 km in diameter) and cold (3.7 °C) caldera lake, has led to minimal research on the area. We present the first detailed characterization of the rocks from the only historical eruption of Krenitsyn Peak (November 1952) and a brief description of the ancient lava and pyroclastic density current (PDC) deposits that make up the building of the volcano. The 1952 eruptive products are represented by two-pyroxene andesites (59.2–63.3 wt.% SiO2), and the older lava and pyroclastic flow rocks consist of two-pyroxene andesites and dacites (62–67.6 wt.% SiO2). Almost all samples belong to the calc-alkaline, medium-K, and medium-Fe series, and the pumiceous lapilli from the 1952 eruption fall into the low-Fe series. The minerals exhibit signs of magma mingling, including relic high-Ca (up to An92) plagioclase cores with signs of dissolution and recrystallization, and oscillatory-zoned pyroxene.

This paper presents a description of the fieldwork conducted in Krasheninnikov Bay on Paramushir Island in July–August 2025 by researchers from the Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences. The fieldwork was carried out during the Russian Geographical Society’s expedition “Eastern Bastion – Kuril Ridge.” To study volcanic and hydrothermal activity in the area, rock samples were collected from formations composing the unified Pleistocene basement of the Chikurachki, Tatarinov, and Lomonosov volcanoes, as well as samples of lava from these volcanoes. At the summit of Tatarinov volcano, aerial and surface temperature surveys of the crater were performed using an unmanned aerial vehicle equipped with a thermal imaging camera. Mineralogical sampling of fumarolic fields on the volcano was also carried out. To determine the geochemical characteristics of geobiocenoses near active volcanoes, soil sampling and hydrochemical testing of major watercourses in Krasheninnikov Bay were conducted. The collected field material (samples of rocks, waters, and products of fumarolic activity) provides the basis for further mineralogical and geochemical studies.

На основании комплексных структурно-геофизических исследований и обобщения геофизических, гидрогеологических, минералого-геохимических и других данных показано, что термальные поля южной группы Камбального вулканического хребта (Южная Камчатка) входят в состав современной гид­ротермальной системы. Получены новые данные о строении зоны разгрузки парогидротерм до глубины около 300 м. Установлена структурная и гидродинамическая связь двух термальных полей этой группы. Предполагается единое тепловое питание геотермальной системы Камбального хребта, объединяющей все основные группы термальных полей. Based on integrated structural and geophysical studies and generalization of geophysical, hydrogeological, mineralogical, geochemical and other data, it is shown that the southern cluster of thermal fields of the Kambalny volcanic ridge (South Kamchatka) is included in the modern hydrothermal system. New data on the structure of the steam hydrotherm discharge area investigated to a depth of about 300 m have been obtained. The structural and hydrodynamic connection between two thermal fields from this group has been established. The Kambalny ridge geothermal system embracing all major clusters of thermal fields is assumed to have a single deep-seated source of heat supply.

This work considers the occurrence of Hg in a clay strata and pore fluids and conditions of Hg incorporation in sulfides and clay minerals abundant in thermal fields of the Koshelev, Kambalny, and Pauzhetka hydrothermal systems. It is shown that, under physicochemical conditions typical of the studied thermal fields, Hg is mostly incorporated in sulfides (pyrite, marcasite, cinnabar) and clay minerals (kaolinite and montmorillonite) as a result of sorption. Under the conditions of a thermal field, cinnabar is the most stable Hg form, because Fe sulfides are unstable during oxidation. The optimal pH value for Hg sorption by clay minerals (in the absence of chlorides and sulfites) is 3.15. In the presence of Hg-bonding chlorides, sulfites, and other anions, the optimal Hg sorption on layered silicates starts from a pH value of >5. The Hg sorption by clay minerals strongly depends on the local highly dynamic geochemical conditions.

Halotrichite is a widespread mineral in post-volcanic environments and oxidation zones of ore deposits. Halotrichite is stable at temperature up to 70 °C; further heating leads to the formation of an X-ray amorphous phase I. There are reflections of millosevichite (prevailing) and mikasaite appearing in the range of temperatures 340–660 °C. Millosevichite and mikasaite are decomposing at temperatures 660 °C with the formation of an X-ray amorphous phase II. According to data of the synchronous thermal analysis, the transition from halotrichite into anhydrous sulfates is accompanied by the loss of H2O molecules, which makes about 42.9 wt %, the transition to the X-ray amorphous phase II is caused by the loss of SO3, which is ca. 37.4 wt %, associated with two endothermal effects. The thermal expansion of halotrichite is sharply anisotropic, the maximum expansion is determined by the shear deformations of the lattice in its monoclinic plane along the bisectrix of the obtuse angle β, and the minimum one – in the direction of strong S–O–Fe bonds inside [Fe(SO4)(H2O)5]0 complexes. The significant volumetric expansion of halotrichite (9(3)∙10-5 ºC-1) occurs due to the determing role of hydrogen bonds in composition of the crystal structure.

--Based on integrated structural and geophysical studies and generalization of geophysical, hydrogeological, mineralogical, geochemical and other data, it is shown that the southern cluster of thermal fields of the Kambalny volcanic ridge (South Kamchatka) is included in the modern hydrothermal system. New data on the structure of the steam hydrotherm discharge area investigated to a depth of about 300 m have been obtained. The structural and hydrodynamic connection between two thermal fields from this group has been established. The Kambalny Ridge geothermal system embracing all major clusters of thermal fields is assumed to have a single deep-seated source of heat supply.

The Sheveluch volcano is the most active volcano in Kamchatka. The paroxysmal explosive eruption of the volcano that destroyed the lava dome in the volcanic crater continued on April 10–13, 2023. According to various satellite data, the height of the separate eruptive clouds probably exceeded 15 km above sea level. A powerful cyclone, which dominated the entire Kamchatka Peninsula, pulled the eruptive cloud to the west, turned it to the south, stretched it to the north, and directed it to the east from the volcano. The dynamics of the development of ash and aerosol clouds of this eruption is reflected in the animations made from a series of Himawari-9 satellite images in the VolSatView IS from 08:00 UTC on April 10 to 07:00 UTC on April 14 ( http://d33.infospace.ru/jr_d33/materials/2023v20n2/283-291/1683110898.webm ) and of the Arctica-M1 satellite from 16:00 to 21:30 UTC on April 10 ( http://d33.infospace.ru/jr_d33/materials/2023v20n2/283-291/1683821166.webm ). It was noted that the eruptive column was not vertical: for example, at the initial moment of the eruption on April 10 at 13:20 UTC, it deviated to the north–northeast; on April 11, at 12:00 UTC to the northwest; and, on April 12, at 7:00 UTC to the southwest. During the paroxysmal eruption, sulfur dioxide continuously entered the atmosphere, the maximum amount of which was released on April 10–11, as a result of the explosive destruction of the lava dome of the Sheveluch volcano. Ash clouds along with aerosol clouds on April 10–13 were stretched into a strip more than 3500 km long from west to northeast. On April 21–22, the Sheveluch aerosol cloud was observed in the region of the Scandinavian Peninsula. The total area of the territory of Kamchatka and the Pacific Ocean where ash and aerosol plumes and clouds were observed during the April 10–13 eruption was about 3 280 000 km2. The paroxysmal eruption of Sheveluch volcano belongs to the sub-Plinian type because it is characterized by a large height of the eruptive cloud and a long event duration. For this eruption, the Volcanic Explosivity Index is estimated to be 3–4. A detailed description of the paroxysmal explosive eruption of the Sheveluch volcano and the spread of the eruptive cloud was performed based on data from various satellite systems (Himawari-9, NOAA-18/19, GOES-18, Terra, Aqua, JPSS-1, Suomi NPP, Arctica-M1, etc.) in the information system “Remote Monitoring of Kamchatka and Kuril Islands Volcanic Activity” (VolSatView, http://kamchatka.volcanoes.smislab.ru ).

Ground temperature survey at three thermal fields of the southern group of the Kambalny volcanic ridge (South Kambalny Near, Central and Far thermal fields) was carried out. Their current state is characterized. The formation of temperature anomalies is determined by the peculiarities of the geological structure of each thermal field.The maps of temperature surveys obtained in 2021 and 1965 are compared. Changes in the conditions of convective heat flow unloading in the geologic structure of thermal fields are shown. The size of temperature fields on all geologic structures of the southern group of the Kambalny volcanic ridge have significantly increased over time. The area of the most warmed areas of thermoanomalies has increased. The maximum ground temperatures increased by 10 °С on average. Some thermoanomalies (boiling and pulsating water boilers and vapor-gas jets) increased their flow rates and (or) temperature. New warmed areas within the thermal anomalies were discovered.

The crystal structure of magnesian halotrichite has been refined for two samples collected as white efflorescences from the surface of geothermal fields associated with the Koshelevsky (sample VK4-09) and Centralny Semyachik (sample SC2-20) volcanoes (both Kamchatka peninsula, Russia). Halotrichite and its Mg-rich varieties are common products of the acid leaching of rocks, both volcanic and technogenic. The crystal structures of two halotrichite crystals were refined in the P21/n space group (vs. P21/c used previously) with the unit-cell parameters a = 6.1947(2)/ 6.1963(5) & ANGS;, b = 24.2966(8)/ 24.2821(14) & ANGS;, c = 21.0593(8)/ 21.063(2) & ANGS;, & beta; = 96.512(4)/ 96.563(9) o, V = 3149.2(2)/ 3148.3(5) & ANGS;3, Z = 4 to R1 = 0.055 and 0.067 for 5673 and 3936 reflections with I > 2 & sigma;I reflections, respectively. The crystal structure consists of isolated Al(H2O)6 octahedra, SO4 tetrahedra, H2O molecules and [X(SO4)(H2O)5]0 clusters (X = Fe, Mg). The chemical analyses of both samples show their enrichment of Mg at the Fe2+ site. The analysis of geometrical parameters of the crystal structures of halotrichite and its Mg-analogue pickeringite suggests that the localization of O atoms carried out in this work is more accurate and the single-crystal X-ray diffraction data for the first time allowed localization of hydrogen atom positions. The refined number of H2O molecules agrees with the ideal chemical formula. The crystal structure complexity of halotrichite is estimated as IG,total = 2305 bits/cell, which belongs to the family of very complex mineral structures. The contribution of hydrogen bonding system plays a significant role in the overall bonding scheme and the overall complexity of the crystal structure, increasing the Shannon information amount more than twice from IG,total(noH) = 988 bits/cell (no hydrogen atoms) to IG,total= 2305 bits/cell (all atoms including hydrogen). The comparative distribution of halotrichite relative to other Fe-Al hydrated sulfates from the standpoint of structural complexity is considered.

Halotrichite has been identified in geothermal fields of the Kambalny-Pauzhetka-Koshelev region, the Bolshoi Semiachik complex, and the Mutnovsky volcano (Kamchatka, Russia). Halotrichite forms efflorescence on soils heated up to 70°C, around steam-gas vents and boiling springs. Tschermigite, rozenite, szomolnokite, gypsum, alunogen, barite, melanterite, hexahydrite, and minerals of the copiapite, alunite and voltaite groups were found in close association with halotrichite. The chemical composition of halotrichite samples from different geothermal fields is similar and characterized by Mg substitution in the Fe2+ position, with Fe2+:Mg ratio ranging from 90:10 to 50:50, and also by Fe3+ substitution in the Al position in some samples, with Al:Fe3+ reaching up to 85:15. Halotrichite is a typical mineral of low-temperature volcanic setting, formed as a result of alteration of parent minerals by hydrothermal fluid and represents an intermediate form of crystallization of leached elements. At the same time, the local conditions of mineral formation — such as variations in Eh, pH, surface temperature, and elemental composition — do not reflect in the chemical composition or other thin typomorphic features of halotrichite. The mechanism of halotrichite formation is probably identical in both geothermal fields and zones of oxidation of sulfide deposits.

Five samples of voltaite-group minerals from post-volcanic occurrences (geothermal fields and solfatara at pyroclastic flow) and from pseudofumaroles born by coal fires are characterized by single-crystal X-ray diffraction, scanning electron microscopy and electron microprobe analysis. The studied minerals include ammoniomagnesiovoltaite, ammoniovoltaite, voltaite and magnesiovoltaite. The quadrilateral of chemical compositions is determined by monovalent cations such as (NH4)+ and K+ and divalent cations such as Fe2+ and Mg2+. Minor Al can occur in the Fe3+ site. Minor amounts of P, V can occur in the S site. Ammonium members are described from geothermal fields, expanding the mineral potential of this type of geological environment. All minerals are cubic, space group Fd-3c, a = 27.18–27.29 Å, V = 20079–20331 Å3, Z = 16. No clear evidence of symmetry lowering (suggested for synthetic voltaites) is observed despite the chemical variation in the studied samples. Ammonium species tend to have a larger a lattice parameter than potassium ones due to longer distances (A = N or K). The systematically shorter obs (Me2+ = Fe, Mg; ϕ = O, H2O) in comparison to calc bond lengths can be explained as a consequence of mean bond length variation due to significant bond length distortion in Me2+ϕ6 octahedra Me2–O2—2.039–2.055 Å; Me2–O4—2.085–2.115 Å; and Me2–Ow5—2.046–2.061 Å, with bond length distortion estimated as from 0.008 to 0.014 for different samples.

The results of field work at the active volcanoes Alaid and Ebeko, located in the northern part of the Kuril Island Arc, carried out in June−July 2023 are described. At Alaid volcano, the first survey of lava flows and fumarolic mineralization products of the 2022 eruption was carried out at various heights, including the summit, and geological sampling of the Taketomi cone and eruptive rocks of the eastern coast of Atlas Island was also conducted. An aerial photo and area temperature survey of the area occupied by the products of the 2022 eruption was undertaken at the summit of Alaid volcano using a high-precision quadrocopter equipped with a thermal imaging camera. At Ebeko volcano, mineral samples were taken from fumarole sites located on its eastern slope, and an aerial photo and area temperature survey were done.

Our multiyear studies have enabled us to make maps showing magnetic anomalies ΔTa for major geothermal systems in the Pauzhetka area of southern Kamchatka. Magnetic fields possess both general characteristics and individual features for each object of study. The Nizhne-Koshelev vapor-dominated geothermal field is identified on the basis of a set of linear negative magnetic anomalies confined to thermal-controlling tectonic faults. The Pauzhetka geothermal field is characterized by an inhomogeneous structure of the anomalous magnetic field ΔTa: the northwestern area has a quiet, slightly negative magnetic field, showing that this part of the field is dominated by lateral spreading of hydrothermal fluids from the upper aquifer; the southeastern part has numerous sign-varying magnetic anomalies of high intensity confined to acid–intermediate subvolcanic bodies. The South Kambalnyi group of thermal fields is characterized by a lower absolute value of magnetic induction Т compared with the Pauzhetka and the Nizhne-Koshelev geothermal fields, showing that the rocks of the Kambalnyi volcanic range are more intensely altered by hydrothermal and metasomatic processes, probably as a result of a long-continued action of convective heat flow.

The new flank eruption named after G.S. Gorshkov started on 18 February, 2021 at Klyuchevskoy volcano (Kamchatka). The Gorshkov vent has erupted after a long time ( 30 years) dominance of terminal eruptions, on the lower altitude ( 2850 m a.s.l.) of the volcano. Lavas of Gorshkov vent are basalts–basaltic andesites (51.6–53.26 wt

Alunogen, Al2(SO4)3·17H2O, occurs as an efflorescent in acid mine drainage, low-temperature fumarolic or pseudofumarolic (at coal fires) terrestrial environments. It is considered as one of the main Al-sulfates of Martian soils demanding comprehensive crystal chemical data of natural terrestrial samples. However, structural studies of natural alunogen were carried out in 1970s without localization of H atoms and have not previously been performed for samples from geothermal fields, despite the fact that these environments are considered as proxies of the Martian conditions. The studied alunogen sample comes from Verkhne-Koshelevsky geothermal field (Koshelev volcano, Kamchatka, Russia). Its chemical formula is somewhat dehydrated, Al2(SO4)3×15.8 H2O. The crystal structure was solved and refined to R1 = 0.068 based on 5112 unique observed reflections with I > 2σ(I). Alunogen crystalizes in P-1 space group, a = 7.4194(3), b = 26.9763(9), c = 6.0549(2) Å, α = 90.043(3), β = 97.703(3), γ = 91.673(3) °, V = 1200.41(7) Å3, Z = 2. The crystal structure consists of isolated SO4 tetrahedra, Al(H2O)6 octahedra and H2O molecules connected by hydrogen bonds. The structure refinement includes Al, S and O positions that are similar to previous structure determinations and thirty-four H positions localized for the natural sample first. The study also shows the absence of isomorphic substitutions in the composition of alunogen despite the iron-enriched environment of mineral crystallization. The variability of the alunogen crystal structure is reflected in the number of “zeolite” H2O molecules and their splitting. The structure complexity of alunogen and its modifications ranges from 333-346 bits/cell for models with non-localized H atoms to 783-828 bits/cell for models with localized H atoms. The higher values correspond to higher hydration state of alunogen.

Alunogen, Al2(SO4)3·17H2O, occurs as an efflorescent in acid mine drainage, low-temperature fumarolic or pseudofumarolic (such as with coal fires) terrestrial environments. It is considered to be one of the main Al-sulphates of Martian soils, demanding comprehensive crystal-chemical data of natural terrestrial samples. Structural studies of natural alunogen were carried out in the 1970s without localization of H atoms and have not been previously performed for samples from geothermal fields, despite the fact that these environments are considered to be proxies of the Martian conditions. The studied alunogen sample comes from Verkhne–Koshelevsky geothermal field (Koshelev volcano, Kamchatka, Russia). Its chemical formula is somewhat dehydrated, Al2(SO4)3·15.8H2O. The crystal structure was solved and refined to R1 = 0.068 based on 5112 unique observed reflections with I > 2σ(I). Alunogen crystalizes in the P-1 space group, a = 7.4194(3), b = 26.9763(9), c = 6.0549(2) Å, α = 90.043(3), β = 97.703(3), γ = 91.673(3) °, V = 1200.41(7) Å3, Z = 2. The crystal structure consists of isolated SO4 tetrahedra, Al(H2O)6 octahedra and H2O molecules connected by hydrogen bonds. The structure refinement includes Al, S and O positions that are similar to previous structure determinations and thirty-four H positions localized for the natural sample first. The study also shows the absence of isomorphic substitutions in the composition of alunogen despite the iron-enriched environment of mineral crystallization. The variability of the alunogen crystal structure is reflected in the number of the “zeolite” H2O molecules and their splitting. The structural complexity of alunogen and its modifications ranges from 333–346 bits/cell for models with non-localized H atoms to 783–828 bits/cell for models with localized H atoms. The higher values correspond to the higher hydration state of alunogen.