This paper describes the chemical composition of the thermal waters discharging on the northwestern slope of the active Ebeko Volcano in the Yuriev River valley. We are using continuous multiyear observations of the evolution of chemical and isotope compositions to estimate the response of volcanic events to the state of the hydrothermal system. It is shown that phreatomagmatic eruptions of the volcano were preceded by a change in the chemical and isotope compositions of thermal waters caused by increased inflow of magmatic volatiles into the system. The springs are observed to show increased concentrations of anion-generating components (chloride, sulfate, and fluorine ions) with concurrent increases in heavier isotopes of oxygen and hydrogen (deuterium) toward “andesitic” water. Recalling that the changes were detected a few months before the eruption, we infer that such geochemical effects can serve as predictive markers when monitoring the state of the volcano.

Remote surveillance techniques from unmanned aerial vehicles (UAVs) equipped with thermal infrared cameras are a progressive platform for effective monitoring of hard-to-reach thermal objects. This paper presents the first results of UAV application to the research of five thermal objects on the Kuril Islands. Four of them (the Kipyashchaya River on Iturup Island, Lake Biryuzovoe on Simushir Island, Yankich Island, and the Yurieva River on Paramushir Island) are associated with active volcanoes. Heat maps with precise geographical reference have been obtained for all sections of gas hydrothermal discharge. Air thermometry for the Kipyashchaya River and Yankich Island were verified by ground data and real atmospheric attenuation coefficients were obtained for different flight altitudes under observed meteorological conditions. The first data on the parameters of the thermal plume from the hot Yurievа River flowing into the Sea of Okhotsk were obtained.

For monitoring hard-to-reach thermal facilities, remote surveillance techniques from unmanned aerial vehicles (UAVs) equipped with a thermal infrared camera represent a progressive platform for rapid information collection. This paper presents the first results of such an application of UAVs to study five thermal objects on the Kuril Islands. Four of them (Kipyashchaya Riwer on Iturup Island, Lake Biryuzovoye on Simushir Island, Yankich Island and Yurieva River on Paramushir Island) are associated with active volcanoes. Heat maps with precise geographical reference have been obtained for all sections of gas hydrothermal discharge. For Kipyashchaya River and Yankich Island verification of air thermometry by ground data was performed and real atmospheric attenuation coefficients were obtained for different flight altitudes under observed meteorological conditions. The first data on the parameters of the thermal plume from the hot Yurievа River flowing into the Sea of Okhotsk were obtained.

This paper provides information on the 2022 eruptive activity of Ebeko Volcano. Phreatic explosions had been occurring in the crater lake from January 22 to June 13 due to water seepage through a plug in the upper part of the magma conduit with subsequent boiling. Vulcanian type explosions started since June 14 and dried the lake. The ash particle-size distribution changed toward smaller sizes. Petrographic, mineralogical, and geochemical studies of the tephra define this period as a phreatomagmatic eruption based on the presence of fresh juvenile material. Interaction between magma and waters of the Ebeko hydrothermal system results in its depletion in alkali and enrichment in silica. We hypothesize that the formation of amorphous water-bearing silica in the form of numerous segregations and its subsequent dehydration can favor the volcano’s explosive activity.

Lake Kipyashchee (Boiling) with an area of ~4.6 ha and a maximum depth of 25 m fills the explosion funnel near one of the extrusive domes of the Golovnin volcano caldera. The water of the lake is ultra-acid (рН = 2.2–2.5) of the chloride-sulfate type with a mineralization of 2.0–2.2 g/l. The water temperature on the surface varies from 30 to 100°C, the average is 37°C. The flow of the lake is carried out through the Protoka in the lake Goryachee (Hot) is 120 l/s (August 2021). The hydrothermal output of magmatic Cl and S (as SO4) from Lake Kipyashchee is 10 t/day and 5.4 t/day, respectively. For the first time, the total diffusive removal of carbon dioxide from the surface of Lake Kipyashchee was estimated as 5.4 tons/day. Obtained from the results of field work in 2020–2021 geochemical data indicate an increase (compared to 2015) in hydrothermal activity in the Golovnin volcano caldera.

The paper provides information about the eruptive activity of the Ebeko volcano in 2022. From January 22 to June 13, phreatic explosions occurred in the crater lake caused by water seeping through the plug formed in the upper part of the magma channel and its boiling. On June 14, Vulcanian explosions began, destroying the lake. The granulometric composition of the ashes has changed in the direction of reducing the particle size. Petrographic and mineralogical-geochemical studies of tephra allow us to define this period as a phreatomagmatic eruption by the presence of fresh juvenile material. It is established that the interaction of magma with the waters of the hydrothermal system of the Ebeko volcano leads to its depletion with alkali metals and enrichment with silica. It is suggested that the formation of amorphous water-containing silica in the form of numerous separations and its subsequent dehydration may contribute to the explosive activity of the volcano.

Lake Kipyashchee ~4.6 ha in area whose greatest depth is 25 m fills an explosion crater near an extrusive dome in the Golovnin caldera. The lake water is ultra acid (рН 2.2–2.5), is of the chloride–sulfate type with a salinity of 2.0–2.2 g/L. The water temperature varies between 30 and 100°С at the surface, with the mean value being 37°С. The lake emptied itself via Protoka into Lake Goryachee at a rate of 120 L/s in August 2021. The hydrothermal drainage of magmatic Cl and S (in the form SO 4 ) from Lake Kipyashchee is 10 and 5.4 t/day, respectively. The first ever estimate of the total diffusion output of carbon dioxide from the surface of Lake Kipyashchee is over 5.4 t/day. The geochemical data acquired during the 2020–2021 field surveys indicate an increase (compared with 2015) in the hydrothermal activity in the Golovnin caldera.

We have obtained new data on the chemical composition (including trace elements) and discharge of the Golubye Ozera ultra acid boiling springs which emit water on the southwestern slope of Baransky Volcano, Iturup Island. It is shown that the cation composition corresponds to solution of 1 g host rock and 1 L water. We carried out hydrologic and hydrochemical measurements to find the total hydrothermal release of magmatic volatiles Сl and S (in the form SO4) along the beds of the main streams that drain the solfataric fields and springs of Baransky Volcano (Kipyashchy Creek and Sernaya River) and estimated the chemical erosion affecting the volcanic edifice. The total measured hydrothermal discharge of Cl and SO4 into the Pacific Ocean reaches 14 t/d and 41 t/d, respectively. The mixed chemical erosion affecting the volcanic deposits in the Sernaya R. basin is about 150 t/km2/yr. The contribution of Kipyashchy Creek into the discharge of dissolved rock-forming components is above 30% of total discharge into the Pacific Ocean on the part of the Sernaya River.

The paper reports the appearance of a new crater lake on the Ebeko volcano. There has been no thermal lake within the Northern Crater since mid-2006. The last eruption began on October 19, 2016 and ended on November 19, 2021. The pyroclastic cone of the new crater, which was named Korbut Crater, rose within the Northern Crater. There was strong fumarolic activity in the Korbut crater, which persists today. The lake in the still erupting Korbut crater was first recorded by the authors on a satellite image from September 17, 2021; already on a satellite image from September 25, the crater was dry again. After the end of the Ebeko eruption, due to the intensive flow of fluid with bottom fumaroles and due to a large amount of meteoric precipitation, a lake was formed in the Korbut crater (Sentinel 2 satellite data of December 11, 2021). In January 2022, the authors examined the Korbut crater: the diameters of the lake were 61 and 80 m (latitude and meridian, respectively), the mirror area was 4.5 thousand m2, and water temperature was 43°C. A brief literature review of the existence of thermal lakes on the northern flank of the Ebeko volcano is given.

This paper reports on new data concerning the chemical and isotopic composition of volcanic gases, the emission of volcanic SO2 and of soil CO2 at the active Ebeko Volcano. The volcano erupted in 2009, 2010, 2011, from October 2016 to November 2021. The composition of volcanic gases for 2003–2016, 2021 was obtained by straightforward sampling of the fumaroles. The high-temperature gas (420–529°С) has a composition that is typical of Kuril magmatic gases with an atomic ratio C/S <1 and the concentration of HCl 5–7 mmol/mol; the isotopic composition of the condensates: δD ~ –24, δ18O = 2.6–4.9. We have identified geochemical precursors of the eruption: increasing concentrations of CO2, Н2, SO2, H2S, and HCl; decreasing C/S ratio down to values below 1, which is characteristic for magmatic gases at the Kurils; increasing temperature; heavier isotopes of δD and δ18O in condensates of volcanic vapor; increasing gas flux. The accumulation chamber technique was used to measure a high soil flux of CO2 in two thermal fields (reaching 10 442 g/m2/day), which exceeds the visible fumarolic output (~50 t/day as against ~40 t/day). The flux of SO2 from the active crater was measured using a DOAS scanning HC spectrometer in 2020 and in 2021, and was 99 ± 28 and 9 ± 2.7 t/day in gas plumes, and 747 ± 220 and 450 ± 130 t/day in ash plumes, respectively. The decreasing emission of SO2 in August 2021 is here related to degassing of the magma before the termination of the eruption.

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.

The article provides information about nival-volcanogenic, possibly glacial-volcanogenic, mudflows (lahars) on three streams on the south side of Atlasov Island (Kuril Islands, Russia). The island is an active stratovolcano Alaid, 2339 m asl high. The effusive-explosive eruption of the Alaid volcano began on September 10, 2022 and continues to the present day. Strombolian activity of the apical cone and lava outflow is observed. Lava filled the summit caldera by September 27. The lava flow then crossed the southern part of the caldera crest and began to descend down the erosional depression at the tops of the catchments of three unnamed streams. Photography and satellite images showed the presence of mudflow transformation of stream beds and slopes, and mudflows fan at the mouths of the streams. Analysis of meteorological and volcanological data showed that the formation of lahars was caused by rapid melting of snow/ice under the influence of lava flow and it occurred between September 29 and October 2.

The data acquired during the field work in 2017 were used to carry out a comprehensive geochemical study of thermal occurrences on Urup Island, which is part of the southern Kuril island arc. It was shown that the thermal waters of Berg Volcano concentrated in the caldera which is open westward at various distances from the extrusive dome are warm (Т up to 40°С), acid (рН 3.5–3.8) of the SO 4 –Cl–Ca type with mineral content reaching 2.5 g/L. The springs of Tri Sestry Volcano situated at its base near Cape Klyuchevoi have temperatures reaching 45°С, рН < 3, and are of the SO 4 –Cl–Ca type with mineral content reaching 1.9 g/L. The isotope composition of water in these two groups of springs is close to that of local meteoric water. The ratios between the concentrations of main cations and the microcomponent composition are generally in agreement with the composition of the host rocks. We note that the Berg Volcano springs show a well-pronounced negative Eu anomaly in the distribution of rare earth elements. The anion composition, the isotope composition of sulfur in the dissolved sulfate (between +15.2 and +21.6‰), as well as the Cl/B and Cl/Br ratios, all indicate the involvement of magmatic volatiles in the formation of these waters. The total measured discharge of Сl and SO 4 by the Berg springs is 9 ± 1.3 t/d and 23.3 ± 3.4 t/d, that for the springs on Cape Klyuchevoi is 0.5 ± 0.2 t/d and 2.3 ± 0.8 t/d, respectively. A preliminary estimate for the chemical erosion affecting the Berg Volcano edifice by thermal waters is 700–800 t/km 2 /yr.

The paper presents the results of integrated geophysical observations of the Ebeko Volcano’s activity in late 2018 and early 2019. The instrument complex for observation was located at the Severo-Kurilsk seismic station at a distance of 7.2 km far from the volcanic crater. Three types of response in the vertical component of the electric field of the atmosphere have been distinguished during the drift of eruptive clouds from the Ebeko Volcano’s explosions, which gives evidence for various mechanisms of their occurrence. The registration of infrasonic acoustic signals in the near zone made it possible to estimate the trinitrotoluene equivalent for the strongest explosions, which was calculated to be about 100 kg of trinitrotoluene. The authors have revealed certain regularities in the dynamics of the volumetric activity of radon, associated with variations in meteorological values and hydrological features of the registration point. A long period of its activity and the proximity of the observation point to the crater give reason to suggest Ebeko Volcano to be a natural laboratory for studying the mechanisms of eruptions.

Growth of explosive activity of Ebeko volcano in April–June 2020

The data obtained during the fieldworks in July 2016 were used for the geochemical description of thermal manifestations of Ketoi and Pallas Peak volcanoes on Ketoi Island in the middle of the Kuril Island arc. It is shown that the older edifice of Ketoi Volcano hosts a high temperature hydrothermal system whose surface manifestations are concentrated in the eroded crater of the volcano. Two main types of thermal water are discharged there: the acid and low-acid waters of the Ca–SO 4 composition in thermal pools that are diluted to varying degrees with meteoric water, and boron-rich neutral boiling water of the Na–Ca–SO 4 composition. The isotopic composition of both water types is similar to that of the local meteoric waters. Calculation of mineral saturation indices for hydrothermal minerals, as well as the behavior of boron, suggest that the waters of the first type are formed nearer the surface, while the boiling sulfate waters are most likely derived from steam condensates formed at depth at a temperature of approximately 200°С. The thermal springs related to Pallas Peak Volcano discharge acid sulfate chloride water. The total measured hydrothermal output of Cl and SO 4 from Ketoi and Pallas Peak volcanoes is 8.5 t/day and 30 t/day, respectively.

This paper reports a detailed geochemical study of thermal occurrences as observed in the edifice and on the flanks of Mendeleev Volcano, Kunashir Island in August and September 2015. We showed that three main types of thermal water are discharged there (neutral chloride sodium, acid chloride sulfate, and acid sulfate types); these waters exhibit a zonality that is typical of volcano-hydrothermal island arc systems. Spontaneous and solfataric gases have relatively low 3 He/ 4 He ratios, ranging between 5.4Ra and 5.6Ra, and δ 13 C-CO 2 between –4.8‰ and –3.1‰, and contain a light isotope of carbon in methane (δ 13 C ≈ –40‰). Gas and isotope geothermometers yield relatively low temperatures around 200°C. The isotope compositions in all types of water are similar to that of local meteoric water. The distribution of microcomponents varies among different types. The isotope composition of dissolved Sr varies considerably, from 0.7034 as observed in Kunashir rocks on an average to 0.7052 in coastal springs, which may have resulted from admixtures of seawater. The total hydrothermal transport rates of magmatic Cl and SO 4 , as observed for Mendeleev Volcano, are 7.8 t/d and 11.6 t/d, respectively. The natural outward transport of heat by the volcano’s hydrothermal system is estimated as 21 MW.