福徳岡ノ場海底火山活動に伴う変色海水 : 海底火山活動の指標としての変色海水

概要

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Discoloration of surface seawater to white, light-yellow and reddish brown is one of indication of submarine volcanic activity. The discoloration is caused by SiO_2-Al_2O_3-Fe_2O_3-H_2O precipitates formed by neutralization of acid hydrothermal solution with seawater. Discolored seawater samples were collected at Fukutoku-Oka-no-Ba in 1977, 1979 and 1986. In 1977 and 1979 when the volcanic activity was dormant, the discolored seawater was milky-white, which was attributed to relative enrichment of Si to Fe and Al. During the eruption in 1986, the discolored seawater was brownish and was rich in Fe and Al relative to Si. After this eruption, the discolored seawater was enriched Si relative to Fe and Al and was milky-white again. Variation of chemical composition and color of the discolored seawater showed a clear correlation with change of activity of the volcano. This example shows that chemical composition of discolored seawater can tell us chemical characteristics of hydrothermal solution, which is a good indicator for submarine volcanism.
特定非営利活動法人日本火山学会の論文
1996-11-01