Volcanic vapors were collected during 1990–1993 from the summit crater of Kudryavy, a basaltic andesite volcano on Iturup island in the Kuril arc. The highest temperature (700–940°C) fumarolic discharges are water rich (94–98 mole% H2O and have δD values of −20 to −12%o. The chemical and water isotope compositions of the vapors (temperature of thirteen samples, 940 to 130°C) show a simple trend of mixing between hot magmatic fluid and meteoric water; the magmatic parent vapor is similar in composition to altered seawater. The origin of this endmember is not known; it may be connate seawater, or possibly caused by the shallow incorporation of seawater into the magmatic-hydrothermal system. Samples of condensed vapor from 535 to 940°C fumaroles have major element trends indicating contamination by wall-rock particles. However, the enrichment factors (relative to the host rock) of many of the trace elements indicate another source; these elements likely derive from a degassing magma. The strongest temperature dependence is for Re, Mo, W, Cu, and Co; highly volatile elements such as Cl, I, F, Bi, Cd, B, and Br show little temperature dependence. The Re abundance in high-temperature condensates is 2–10 ppb, sufficient to form the pure Re sulfide recently discovered in sublimates of Kudryavy. Anomalously high I concentrations (1–12 ppm) may be caused by magma-marine sediment interaction, as Br/I ratios are similar to those in marine sediments.

The high-temperature (>700°C) fumaroles have a relatively constant composition (∼2 mol% each C and S species, with SO2/H2S ratio of about 3:1, and 0.5 mol% HCl); as temperature decreases, both St and CI are depleted, most likely due to formation of native S and HCl absorption by condensed liquid, in addition to the dilution by meteoric water. Thermochemical evaluation of the high-temperature gas compositions indicates they are close to equilibrium mixtures, apart from minor loss of H2O and oxidation of CO and H2 during sampling. Calculation to an assumed equilibrium state indicates temperatures from 705 to 987°C. At high temperature (≈900°C), the redox states are close to the overlap of mineral (quartz-fayalite-magnetite and nickel-nickel oxide) and gas (H2OH2SO2H2S) buffer curves, due to heterogeneous reaction between the melt and gas species. At lower temperatures (<800°C), the trend of the redox state is similar to the gas buffer curve, probably caused by homogeneous reaction among gas species in a closed system during vapor ascent.

On the basis of the chemical, isotopic and thermodynamic characteristics of fluids sampled between 1964 and 1989 a genetic model description is given for fumaroles of the Mutnovsky volcano. There are three individual groups of fumaroles in the Mutnovsky crater which show stable activity for a long period of time: “the Active Funnel” (temperatures exceed 600°C), the “Upper Field” (up to 320°C) and the “Bottom Field” (from 100 to 150°C). The three principal zones of emission have different gas composition, water isotopic composition, radioactivity and 3He/4He ratios. The abundance of magmatic components in the high-temperature fumaroles of the “Active Funnel” is much higher than those in gases from the other groups. Emission rate of SO2 from the “Active Funnel” is about 200 t/d, which requires complete degassing as a minimum of 1 km3 of magma every 20 years. Fluids of the “Upper Field” contain up to 80% of steam from the Mutnovsky geothermal system. Temperature variations of the “Bottom Field” fumaroles (from 97°C before 1982 to 151°C in 1989) result from changes in hydrological conditions in the crater. Evaporation of high-saline acid brine which is formed in the interior of the volcano is responsible for the composition of the “Bottom Field” gas-steam discharges.

Gas samples have been collected at the place of magma effusion during the 1988 flank eruption of Klyuchevskoy, for the first time in the course of studies at this volcano. The high-temperature gases (1000–1100°C) are rich in water and halogens but depleted in sulphur. Their molar composition is close to chemical equilibrium at the collection temperature, while their oxidation state corresponds to redox conditions between FMO and NNO buffers. The isotopic composition of the water (δD = −71 to −44‰; δ18O = +6.3 to +8.4‰, versus SMOW) plots within the field of “primary magmatic” waters. The isotopic composition of H2 (δD = −187‰ to −160‰) is consistent with isotopic equilibrium between H2 and H2O in the conditions of emission. Both the chemistry of the gases and the low δ13C of carbon dioxide (−11.6‰, PDB) suggest extensive magma outgassing occurred during the course of the eruption.

The 1996 short-lived subaqueous eruption at the Karymsky caldera lake suddenly changed the composition of the lake water. The lake, with a surface area of ∼10 km^2 and a volume of ∼0.5 km^3, became acidic, increased its salinity to ∼1000 mg/kg, and became dominated by SO4^2- and Ca^2+. Since the eruption, the lake chemistry has evolved in a predictable manner described by simple box model. As a result of dilution by incoming SO4-Ca-Mg-poor water, SO4, Ca, and Mg concentrations follow a simple exponential decrease with a characteristic time close to the residence time of the lake. Na, K, and Cl decrease relatively significantly slower, indicating a continuing input of these constituents into the lake that was initiated during the eruption. Thus, the dynamics of two groups of lake water solutes can be predicted by a simple box model for water and solute mass balance. Key Points Karymsky lake suddenly changed chemistry as a result of the 1996 eruption One-box dynamic model correctly describes the evolution of the lake chemistry The calculated fluxes of chemicals are in a good agreement with the field data

Significant variations in temperature, water chemistry and volume of the lake in the crater of Maly Semyachik volcano, Kamchatka, in 1965–2020 can be divided in three main stages. The first stage, until about the mid-1980s, was characterized by intense volcanic-hydrothermal activity, high (above 40 °C) temperature, high salinity (up to 40 g/l) and an increase in the level (and volume) of the lake. During the second stage, which lasted 25–30 years, since the mid-1980s until the mid-2000s, the lake cooled down, until freezing in winter, the mineralization decreased (up to 1.6 g/l), and the volume of the lake remained almost constant. After the mid-2000s until present, there is a period of activation of the Maly Semyachik volcano, which is expressed in an increase in temperature, mineralization and a sharp increase in the volume of the crater lake. The water balance of the lake and the input and composition of the thermal acid chloride solution are estimated based on the analysis of changes in chemical and physical parameters over time, using a box model.

The Kuril Island arc extending for about 1,200 km from Kamchatka Peninsula to Hokkaido Island is a typical active subduction zone with ∼40 historically active subaerial volcanoes, some of which are persistently degassing. Seven Kurilian volcanoes (Ebeko, Sinarka, Kuntomintar, Chirinkotan, Pallas, Berg, and Kudryavy) on six islands (Paramushir, Shiashkotan, Chirinkotan, Ketoy, Urup, and Iturup) emit into the atmosphere > 90% of the total fumarolic gas of the arc. During the field campaigns in 2015–2017 direct sampling of fumaroles, MultiGas measurements of the fumarolic plumes and DOAS remote determinations of the SO2 flux were conducted on these volcanoes. Maximal temperatures of the fumaroles in 2015–2016 were 510°C (Ebeko), 440°C (Sinarka), 260°C (Kuntomintar), 720°C (Pallas), and 820°C (Kudryavy). The total SO2 flux (in metric tons per day) from fumarolic fields of the studied volcanoes was measured as ∼1,800 ± 300 t/d, and the CO2 flux is estimated as 1,250 ± 400 t/d. Geochemical characteristics of the sampled gases include δD and δ18O of fumarolic condensates, δ13C of CO2, δ34S of the total sulfur, ratios 3He/4He and 40Ar/36Ar, concentrations of the major gas species, and trace elements in the volcanic gas condensates. The mole ratios C/S are generally <1. All volcanoes of the arc, except the southernmost Mendeleev and Golovnin volcanoes on Kunashir Island, emit gases with 3He/4He values of >7RA (where RA is the atmospheric 3He/4He). The highest 3He/4He ratios of 8.3RA were measured in fumaroles of the Pallas volcano (Ketoy Island) in the middle of the arc.

Abstract Prolonged basaltic effusive eruptions at high latitudes can have significant atmospheric and environmental impacts, but can be challenging to observe in winter conditions. Here, we use multi-sensor satellite data to assess sulfur dioxide (SO2) emissions from the 2012–2013 eruption of Plosky Tolbachik volcano (Kamchatka), which lasted ~ 9–10 months and erupted ~ 0.55 km3 DRE. Observations from the Ozone Monitoring Instrument (OMI), the Ozone Mapping and Profiler Suite (OMPS), the Atmospheric Infrared Sounder (AIRS), and the Moderate Resolution Imaging Spectroradiometer (MODIS) are used to evaluate volcanic activity, SO2 emissions and heat flux associated with the effusion of lava flows. Gaps in the primary OMI SO2 time-series dataset occurred due to instrument limitations and adverse meteorological conditions. Four methods were tested to assess how efficiently they could fill these data gaps and improve estimates of total SO2 emissions. When available, using data from other {SO2} observing instruments was the most comprehensive way to address these data gaps. Satellite measurements yield a total SO2 loading of ~ 200 kt SO2 during the 10-month Plosky Tolbachik eruption, although actual SO2 emissions may have been greater. Based on the satellite SO2 measurements, the Fast Fourier Transform (FFT) multi-taper method (MTM) was used to analyze cyclical behavior in the complete data series and a 55-day cycle potentially attributable to the eruptive behavior of Plosky Tolbachik during the 2012 – 2013 eruption was identified.