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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Earth Sci. | doi: 10.3389/feart.2019.00249

Time variation in the chemical and isotopic composition of fumarolic gases at Kusatsu-Shirane volcano Japan

 Takeshi OHBA1*,  Muga YAGUCHI2, Kana NISHINO1, Nozomi NUMANAMI1,  Urumu Tsunogai3, Masanori ITO3 and Ryo Shingubara3
  • 1Tokai University, Japan
  • 2Meteorological Research Institute (MRI), Japan
  • 3Nagoya University, Japan

At Kusatsu-Shirane volcano Japan, the intense seismic activity took place in 2014 and 2018. To investigate the relationship between the activity and the chemistry of fumarolic gas, the gas samples have been repeatedly analyzed. A monotonic decrease in CO2/H2O, He/H2O and N2/H2O ratios since July 2014 to November 2017 suggests the decline of magmatic component. On contrary CH4/H2O ratio significantly increased during the seismically quiet period, suggesting the reduced condition in hydrothermal system favoring to the formation of CH4. The high N2/He ratio in the quiet period suggests the addition of component originating in crustal rock hosting hydrothermal system. The N2/He ratio in 2018 was definitely lower than the ratio in 2014, indicating the evolution of magma brought by the degassing. The δD(H2O), δ18O(H2O) and CO2/H2O ratio of fumarolic gas were modeled with the following processes; the generation of vapor phase after the mixing between magmatic gas and a cold groundwater with meteoric origin, the addition of vapor phase with meteoric origin, and the partial condensation of water vapor near surface. Only a single magmatic gas is necessary for the above modeling.

Keywords: volcanic gas, Seismic acitivity, hydrothermal system, Magma, he, N2, CO2, CH4

Received: 02 Oct 2018; Accepted: 05 Sep 2019.

Copyright: © 2019 OHBA, YAGUCHI, NISHINO, NUMANAMI, Tsunogai, ITO and Shingubara. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Takeshi OHBA, Tokai University, Hiratsuka, Japan, takeshi_ohba@tokai-u.jp