1983 年三宅島噴火後の火山ガスの組成変化と火山昇華物

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Miyakejima volcano erupted on October 3, 1983 after 21 years' interval. This paper deals with a geochemical study on the volcanic gases, sublimates and rock samples collceted after the eruption. Immediately after the eruption, the chemical composition of volcanic gases indicates that these samples are mixtures of gases supplied from magma and residual gases in lava expelled by remaining heat. About ten days after, they show characteristic of the latter mainly. This change may be caused by the drain-back of magma. About five months later, remaining fumarolic gases are solely composed of CO_2. Volcanic sublimates found around the fumaroles were mainly salammoniac (NH_4Cl) and other minerals were a little in their variety and amounts. Insoluble chlorine and total fluorine contents in lava and bomb were determined. They show rather uniform distribution with only one exception of a vesicular volcanic bomb. Their insoluble chlorine contents are distinctly higher than those of the 1962-lava samples. Any evidence of the effect of the interaction of hot lava with seawater on halogen contents is not found.
特定非営利活動法人日本火山学会の論文
1984-12-28