伊豆大島火山の 1986 年噴火活動に伴う火山ガスの組成変化

概要

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Chemical and isotopic compositions of volcanic gases and rocks are compared between the samples collected immediately before and after the 1986 eruption of Izu-Ohshima volcano. Around the pit crater of Mt. Mihara, the CO_2 and H_2 contents in fumarolic gases increased before the eruption. The chemical composition of volcanic gases from Mt. Mihara (A crater area) indicates that they are mainly of magmatic origin. The gases from the craters B and C, both formed by fissure eruption, did not come from the magma but were expelled from the hot lava and scoria. δ^<13>C values show that CO_2 in these gases were derived from organic matters. This is consistent with the very short duration of fumarolic activity at the B and C crater area. Volcanic sublimates found around the high temperature fumaroles at the A crater area were mainly sulfate minerals. At the B and C crater area, copper chloride (CuCl_2 etc.) and copper oxide (CuO etc.) dominated at the B crater area. Most of the sublimates from the C crater area were salammoniac (NH_4Cl). Chlorine and fluorine contents of lava and scoria from A crater are found to be relatively uniform. On the other hand, those from B and C crater groups are highly valuable, and strong correlation is found between chlorine and fluorine contents.
特定非営利活動法人日本火山学会の論文
1988-06-30