Stable isotope study of the Atosanupuri-Kawayu geothermal system, Eastern Hokkaido, Japan

The isotopic ratios of water and sulfur species in the Atosanupuri-Kawayu volcanic geothermal system, Hokkaido, Japan, are in accordance with a hydrological model which assumes: (1) the hot fluid ascends from depth and boils at the bottom of the Iwoyama dome in the Atosanupuri Volcano; (2) the steam and most of the hydrogen sulfide escape to the solfatara of the Iwoyama: and (3) the residual hot water issues at Kawayu Spa about 3 km to the north of the dome, after dilution and cooling by local meteoric waters. The temperature of boiling, the isotopic ratios and chloride content of the residual hot water and its fraction in the Kawayu hot spring waters were calculated from the observed isotopic and chemical data and certain assumptions. The results are in accordance with those estimated by shallow ground-temperature distribution in this area.