On the Occurrence of Geothermal Products in Japan

Geothermal areas in Japan are distributed along Quaternary volcanic zones. Fumaroles and hotsprings in these areas issue from younger volcanic rocks and origin of them seems to be related to Quaternary volcanic activities, though a few jet from Tertiary granitic rocksThermal activities in these areas are divided into two types : One is caused by emanation of shallow magmas of active volcanoes like as Atosanupuri and Showa-shinzan in Hokkaido and Iwojima in Kyushu which are characterized by high temperature and strongly acidic gases, the other is originated by consolidation of deeper magmas.One of characteristic appearances of geothermal areas in Japan is that surface thermal indications are poor. But, according to investigations made in some areas, it has become clear that geothermal products are reserved in porous beds and permeable hard rocks of younger volcanics and their basements. For example, hot water occurs from Tertiary formation covered by younger andesite lava flow in spite of lacking remarkable surface indications, in Matsukawa area, Iwate Prefecture. Occurrences in other areas may be analogous to that of Matsukawa.To know more clearly subsurface structures in geothermal areas, investigations by drilling are necessary.