The radioactive springs related with the Hiroshima Granite, one of the largest batholith in Japan, are distributed near the contact between the granite and wall rocks. In the Kurobe geothermal field the hot springs are distributed near the contact, too. Similar distribution pattern was recognized in west-central Alaska (Miller et al., 1975). Structural studies on intrusive bodies revealed that the fractures are often present near the contact between the granite and wall rocks (e. g. Balk, 1937). They would be caused by the upward movement of the granitic pluton or by the high magma pressure. It was also pointed out that they would be of tension type (Balk, 1937; Koide and Bhattacharji, 1975). Some of the hot springs related with the granite may be tectonically controlled by such a fracture system.
A method to estimate heat flow in steaming ground is presented by means of measurements of surface temperatures and near-surface underground temperatures, based on equations of heat and mass transfer in the near-surface underground. Total heat flow Q, which includes the heat transferred by conduction and convection, is expressed as follows:Q=H(To-Tair)(i(T∞)-cWTair)/cg(T∞-To)where H is a coefficient of surface heat transfer, To surface temperature, Tair air temperature, Tw boiling point of water, cg specific heat of steam, cw specific heat of water and i(T∞) enthalpy of steam at temperature T∞. This method was applied to the Showa-shinzen geothermal area, and total heat discharge was estimated at 2.5×107cal/sec which is nearly equal to the value obtained by the heat balance method developed by Sekioka and Yuhara (1974).