Water-vapor isotope fraction in volcanic plume: Estimation from the stable hydrogen and oxygen isotope ratios of water vapor in volcanic plume.

Abstract

In March 2024, we determined the water vapor isotopic composition of the plumes emitted from three different fumaroles (H, Y2, Y3) within the same fumarolic field at Kirishima Iwo-yama using the method described in Takahashi et al. (2019). We also analyzed isotopic composition of the fumarolic vapor condensed water samples collected by the cold trap. As a result, the three plumes exhibited different water vapor isotopic compositions from each other, and these were plotted on the isotopic fractionation line assuming Rayleigh fractionation at the observed temperature. The isotopic composition extrapolated on the meteoric water - magmatic water mixing line was consistent with the estimated value for magmatic water and was generally consistent with the isotopic composition of the condensed water samples. Therefore, it is highly likely that some of the water vapor released from the fumaroles quickly condenses and is removed from the plume.