1986年伊豆大島噴火に伴う変色海水の化学組成

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Discoloration of sea water is one of the remarkable phenomena observed at the time of submarine volcanic activity. Chemical compositions and color tone of discolored sea water change in response to volcanic activity and are regarded as good indicators of the activity. Discolored sea water appeared along the coast of Izu-Oshima insular volcano at the time of the eruption in 1986 and airborne observation and sampling of the discolored sea water were carried out from November, 1986 to March, 1987. The number of the areas where the discolored sea water was observed around the island reached a maximum on Dec.20, 1986 and decreased afterwards. Al/Si and Fe/Si weight ratios also reached their peaks on Dec. 23, 1986 and their variations were very similar to each other and parallel to the variation of the number of the areas. Chemical compositions of almost all the samples were within limited values with Al/Si<1.5 and Fe/Si<0.6. Percentage of Si in those samples is higher than those of Fe and Al and regional variation in the composition were not recognized.
2000-10-25