焼岳火山の噴気の化学・同位体組成

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  • Chemical and Isotopic Compositions of Fumarolic Gases from Yakedake Volcano, Japan
  • ヤケダケ カザン ノ フンキ ノ カガク ・ ドウイタイ ソセイ

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<p>Since the latest phreatic eruption in 1962-1963, Yakedake volcano has remained dormant, but fumarolic activity around the summit area has continued steadily during the past hundred years. Temperature, chemical, and isotopic compositions of fumarolic gases were ascertained for 2013-2017. Discharge temperatures of the most active fumarole were 113-123°C: much lower temperatures than those during the active period. Lower concentrations of HCl and H2 and a lower SO2/H2S ratio coincide with this relative quiescence of the present Yakedake volcano. The apparent equilibrium temperatures estimated from the sulfur reactions were about 250-280°C, which decreased by about 200°Cshortly after the latest eruption and which were lower than the critical temperature of water, suggesting the formation of a volcanic hydrothermal system beneath the summit region. The isotopic compositions of water (D,18O) show that the fumarolic fluids were probably formed by mixing of the magmatic fluids and local meteoric water. The contribution of magmatic fluid to the sampled fumarolic fluids was estimated as about 80-90%, which is higher than the values obtained shortly after the latest eruption. The estimated volcanic hydrothermal system under the volcano is possibly less influenced by local meteoric water, in spite of the low discharge temperature and low concentrations of gas species derived from high-temperature volcanic gas.</p>

収録刊行物

  • 火山

    火山 64 (1), 1-9, 2019-03-31

    特定非営利活動法人 日本火山学会

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