HIReTS法を用いた火山噴気の遠隔温度測定 : 薩摩硫黄島における検証

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Molecular hydrogen (H_2) in fumarolic gases shows the hydrogen isotope exchange equilibrium with coexisting H_2O at a temperature more than 400℃. Recently, we developed a new remote temperature sensing using the characteristics of hydrogen isotopes (HIReTS). In this method, the hydrogen isotopic composition (δD value) of fumarolic H_2 is obtained remotely from the observation of volcanic plume, and the outlet temperature of the fumaroles is estimated from the δD value, assuming that the hydrogen isotope exchange equilibrium is quenched within volcanic plume during the process of admixture between fumarolic gases and air. To verify this new remote temperature sensing at the field which has fumaroles with various temperatures from 100℃ to more than 800℃, we determined both concentrations and δD values of H_2 in the volcanic plume emitted from the summit crater of Satsuma-Iwojima volcano, Japan. The average H_2 concentration of the plume samples (n=22) taken at the crater rim was 3.8ppm (from 1.0ppm to 14.4ppm), while that taken apparently outside the volcanic plume was less than 0.65ppm. The reciprocal of the H_2 concentration in the plume samples showed a good linear relationship with the δD values (r^2=0.994). By extrapolating the linear relationship to exclude the contribution of the tropospheric H_2, we estimated that the δD value of the fumarolic H_2 to be -185.0±2.5‰ and the outlet temperature to be 813±10℃. The estimated temperature was in good agreement with the maximum outlet temperature of the fumaroles inside the crater. The remote temperature sensing using HIReTS can be applicable to obtain the maximum fumarolic temperature remotely in many volcanoes.
2013-09-30

HIReTS法を用いた火山噴気の遠隔温度測定 : 薩摩硫黄島における検証

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