This report presents a brief description of the expeditionary work performed by the staff of the Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences as part of the research topic and the Russian Science Foundation project on the Kuril Islands in the summer of 2022. In order to study the chemical erosion of volcanic islands and to assess the hydrothermal removal of magmatic volatiles, in addition to the works carried out in 2020 and 2021, hydrological and hydrochemical studies were comducted on the rivers draining the slopes of the volcanic ridges of the Paramushir, Onekotan and Shiashkotan islands. For the first time, with the help of a quadrocopter, sampling of the endorheic Lake Koltsevoe, which occupies the caldera of the Tao-Rusyr volcano (Onekotan Island), was carried out. A detailed hydrochemical testing on the thermal fields of the active volcanoes Sinarka and Kuntomintar (Shiashkotan Island) was performed, a number of regime observations of the Upper Yuryevsk springs (Paramushir Island) were replenished. In order to construct orthophotomaps and determine the boundaries of thermal anomalies, aerial and infrared surveys were carried out at the main study sites in parallel with geochemical sampling. A large number of water and gas samples were taken for further analytical studies during the expedition and the collection of sediments was replenished.

This report provides a brief description of the field work on the Kuril Islands. It was performed within the framework of the R&D theme, projects of the RSF and the RFFR, which are realized in the laboratory of postmagmatic processes of the Institute of Volcanology and Seismology FEB RAS. Hydrological and hydrochemical works were performed on the rivers draining the slopes and thermal fields of the Sinarka, Kuntomintar volcanic massifs (Shiashkotan Island), and the Vernadsky and Karpinsky Ridges (Paramushir Island). The study of the chemical erosion of volcanic islands and the assessment of the hydrothermal export of magmatic volatiles are the goals of this work. Infrared photography was taken and the total flux of volcanic SO2 and diffusion flux of CO2 were measured on thermal fields in the caldera of Golovnin volcano. A detailed hydrogeochemical survey was made on the thermal fields of the Ebeko volcano to study the relationship of volcanic and hydrothermal activity of the volcano. For further analytical work, a large number of water and gas samples were taken and a representative collection of rocks and sediments was collected during the expedition.

This report gives a brief description of field work on the Kuril Islands in summer 2021 carried out by staff of the Institute of Volcanology and Seismology of  FEB RAS within the framework of the Institute research theme and projects of the Russian Science Foundation (RSF) and Russian Fund for Basic Research (RFBR). To study chemical erosion of volcanic islands and to estimate hydrothermal export of magmatic volatiles, hydrological and hydrochemical works were carried out on the rivers draining the slopes and thermal fields of the Baransky volcano and the Bogdan Khmelnitsky volcanic massif (Iturup Island). Detailed hydrochemical studies with water sampling at different depths and a bathymetric survey of Lake Kipyashchey located in the caldera of Golovnin volcano (Kunashir Island) were performed. We also proceeded with studying the CO2 diffusion flux through thermal fields and volcanic lakes. In the course of ongoing regime observations on Ebeko volcano (Paramushir Island), aerial and infrared imaging of its near-crater part was carried out. For the first time since the eruption began in 2016, a quadcopter survey of the lake located in the Srednii (middle) crater of the volcano was conducted. For further analytical studies a large number of water and gas samples were taken, and the collection of sediments was replenished.

The chemical and isotopic composition of hot springs at the apical part of the active Ebeko volcano (Paramushir Island, Kuril Islands) is characterized based on the data obtained from fieldwork in 2020–2021. Thermal waters discharging from one of the sources of the Kuzminka River are ultra-acid (рН<2) Al-Ca-SO4-Cl type with mineralization up to 5 g/l and temperature up to 70°С. The anionic composition of waters is formed due to the dissolution in groundwater of acidic volcanic gases, partially «purified» in the main reservoir of the volcano's hydrothermal system. The cationic composition of waters, including rare-earth elements, is formed by isochemical dissolution of host rocks in the equivalent of 5 g per 1 liter of water. Differences in the isotopic composition and ratios of macrocomponents (SO4 /Cl, Al+Fe/Ca+Mg/Na+K) of waters of the near the summit  prings and the northwestern slope suggest the presence of different-level aquifers in the hydrothermal system confined to the edifice of the Ebeko volcano.

На основе гидрогеохимических данных, полученных в результате полевых работ, проведенных на острове Шиашкотан в 2011 г., приводится характеристика различных типов природных вод, включая конденсат фумарольных газов, разгружающихся на западном склона вулкана Кунтоминтар. В исследуемом районе распространены холодные и термальные кислые минерализованные воды, соответствующие сульфатному типу с пестрым катионным составом. Конденсат фумарольных газов относится к хлоридному кальциевому типу с высоким содержанием бора. Формирование химического состава природных вод происходит за счет взаимодействия метеорных вод с гидротермально измененными породами. Газы вулкана Кунтоминтар имеют магматическое происхождение: их конечный состав сформирован в результате подъема флюида к поверхности и значительного разбавления его метеорной водой в близповерхностных условиях.

Приведены новые данные по макро- и микрокомпонентному составу термальных вод, разгружающихся в бассейне р. Юрьевой (о. Парамушир, Северные Курильские острова). Прослежены изменения в химическом составе и физико-химических показателей вод Верхне-Юрьевских источников, произошедшие с начала их исследований в 1957 г. до 2010 г. Дана предварительная оценка геохимической работы источников по состоянию на 2010 г. Рассмотрены условия формирования термальных вод.

Based on the results of expeditionary studies (July 2021), geochemical features of thermal waters (natural manifestations and borehole waters) discharging near or directly on the Sea of Okhotsk and Pacific coasts of the central part of Iturup Island were considered: Reidovskie, Lososevye, Cape Konakov, Goryachie Klyuchi, Dachnye, water-recreational complex «Vannochki». The springs (with the exception of Lososevye) belong to subneutral Cl(Cl-HCO3)-Na waters with salinity less than 10 g/l. The Lososevye springs are of the weakly acidic HCO3-SO4-Ca-Na type with salinity of 3 g/l. The spontaneous gas is dominated by CO2 (Dachnye and Vannochki), N2 (Reidovskie and Cape Konakov) and CH4 (Goryachie Klyuchi). Against the background of a general extremely low content of microelements,  thermal waters are enriched with boron and lithium. The springs are characterized by small (0.1 l/s) to insignificant (0.02–0.05 l/s) flow rates, while wells drilled nearby uncover horizons of pressurized waters.