Gas Emission on Ebeko Volcano, Kuril Islands in 2003–2021: Geochemistry, Flows, and Indicators of Activity

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 CO_2, 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.