Amounts of Some Chemical Components Discharged from Satsuma-Iwo-Jima Volcano in Relation to Their Feeding Sources

Abstract

Annual discharge of several chemical components of fumarolic gases and of hot spring waters are calculated on the basis of the remote sensing measurement of fumarolic SO₂-discharge by OHKITA et al., (1977) and of the estimation of hot-spring water discharges by KAMADA (1964). An examination is made if the present material discharge could be maintained for 1, 000 years only from feeding sources of near surface such as the volcanic body of Iwo-dake, sea water etc. Chlorine may be supplied from sea water. Fluorine content of sea water is very small, and almost all the fluorine in the whole rocks of Iwo-dake must be given off in order to continue the present fluorine discharge for 1, 000 years. Neither the amount of sulfur in the Iwo-dake rocks nor that in sea water is sufficient to maintain the present discharge only for a few years. Aluminum and iron can be supplied if 5% of the Iwo-dake rocks are completely leached by acid waters. Alkali and alkaline earth metal ions can be supplied either from sea water or from the rocks. MATSUO et al., (1974) reported that fumarolic gases of the Iwo-jima volcano have very high δ¹⁸O values (～+7‰). If these high δ¹⁸O values were the result of oxygen isotopic exchange between surface water (including sea water) and near surface rocks, δ¹⁸O value of the whole Iwo-dake rocks should be lowered to 0‰ within 250 years. The result of the calculations strongly suggests that not only heat but also material supply from magma is necessary to maintain the fumarolic and hot spring activities of Iwo-jima volcano.