抄録
Variations in temperature, chemical and isotopic compositions of fumarolic gases discharged from the summit of Yakedake volcano, Honshu, Japan, have been observed since 1965, 2 years after the 1962-63 eruption (phreatic explosions with mud flows). The temperature of 168℃ was recorded in 1965, and has been gradually decreasing since then. The existence of appreciable amounts of H2, HCl and S02 in the fumarolic gases suggests the supply of high temperature gases from magma. The hydrogen and oxygen isotopic compositions of fumarolic condensates suggest that the fumarolic gases are mixtures of magmatic gases and local meteoric water, and that the contribution of local meteoric water to the fumarolic gases has been increasing since 1965. The 1962-63 eruption was possibly caused by the supply of high temperature volcanic gases to the surface mud reservoir which had been previously formed by the fumarolic activity.
