Radionuclide behavior in high-temperature gases from Satsuma Iwojima volcano, Japan

Radionuclide and sulfur measurements were performed on samples from plume and hot fumarolic gas discharged from Satsuma Iwojima volcano, Japan. Such measurements in volcanic plumes contribute to a better understanding of degassing mechanisms (emanation coefficient of metals, degassing magma volume, residence time of the magma). At Satsuma Iwojima, inferred emanation coefficients of 210Pb and 210Po were estimated to be 0.07 and 2.5%, respectively, the lowest values obtained to date in volcanic gases. These values may be “apparent” emanation coefficients, due to the high viscosity of the degassing magma, which prevents efficient degassing of such low concentration components. The volume of the degassing reservoir (rhyolite layer) is estimated to be 0.24 km3, assuming no radionuclide recharge from the underlying basaltic reservoir to the degassing rhyolite.