Geochemical Studies on Volcanic Gases, Waters and Rocks from Iwo-jima

Abstract

The temperature of fumarolic gas ranged from 100 to 128 °C. These gas usually contained few HCl and SO₂, and contained a small amount of H₂S. These facts indicated that acidic gas components were absorbed into the aquifer during the cause of ascent. Hot springs may be classified into three types according to their chemical composition : 1) volcanic thermal water type ; 2) sea water type ; and 3) type of mixture of 1 and 2.δD and δ¹⁸O of waters collected from this island are high. The rocks from Iwo-jima are all trachy andesite with the SiO₂ content of 54-58 %, and with the Na₂O+K₂O content of 9-10 %.