GEOTHERMAL AND HOT SPRING WATER ORIGIN DETERMINATION USING OXYGEN AND HYDROGEN STABLE ISOTOPE IN THE TOYOHIRAKAWA CATCHMENT, HOKKAIDO, JAPAN

Abstract

Jyozankei hot spring located near Sapporo City in Hokkaido is famous for many visitors and
hot spring quality in Japan. Ground temperatures of 220 °C were reached in the Toyoha Mine10 km west of
Jyozankei hot spring where several boreholes less than 2000 m in depth for investigating geothermal water
were drilled. Subsequently, a hydrological investigation to clarify the influence of geothermal development
on Jyozankei hot Spring was performed. Snow, river, well, spring, hot spring and the geothermal borehole
waters in the Toyohirakawa catchment including Jyozankei hot spring were sampled and oxygen and
hydrogen stable isotopes of water were analyzed to determine water origin for hot spring and geothermal
water. As a result, Jyozankei hot spring and the borehole waters were thought to arise from mixed waters of
magmatic and surface waters. Borehole water, from less than 2000 m in depth, was 10 to 30 % of the
magmatic water and Jyozankei hot spring water was less than 10 % of the magmatic water. Surface water
was recharged at the upstream of the Toyohirakawa catchment, with snow from the upper stream of the
northwest catchment being an important resource of surface water for both Jyozankei hot spring water and
geothermal water from the boreholes.