十勝岳62-1火口の火山ガス組成 : 特集: 十勝岳1988～1989年噴火

抄録

Mt.Tokachi was reactivated on December 16, 1988 at the 62-2 crater. Chemical compositions of the volcanic gases from the 62-1 crater have been determined periodically since 1984, and more frequently after the reactivation. There was little change in chemical compositions of volcanic gases collected on August 23, 1988, four months before the eruption. H₂ content in residual gas (R-gas) and HF/HCl ratio showed a remarkable increase on January 25, 1989. These facts indicate tha the volcanic activity was at the highest stage in January, 1989 in this eruptive period. Also, the relative propotion of HF+HCl, SO₂ +H₂S and CO₂ exhibited close correlation with the variation in the volcanic activity. The apparent eqilibrium temperatures for the reaction; SO₂+3H₂=H₂S+2H₂O, suggest that the volcanic gases from the 62-1 crater were contaminated with sulfur at a shallow depth around the summit area.