Some geothermal measurements at the Otake geothermal area

Abstract For the purpose of preparing the fundamental data on the problems of geothermal development, thermal discharge, temperature gradient and thermal conductivity of rock samples were measured at Otake geothermal area. In a geothermal area, generally, heat is discharged by various processes, such as fumaroles, which can be classified under several headings according to their discharge amount, hot springs and hot ground surfaces. The heat flow from the strong fumaroles was measured by condensing the natural steam in the water vessel and the heat flow from the weak ones was measured by using a wet and dry bulb thermometer. Several holes wer drilled in the thermal area to determine the underground temperature gradient which is 1.9 °C/m at the steaming ground and 0.8 °C/m at the ordinary geothermal area. The thermal conductivity of 30 dried core samples was measured in the laboratory and in situ by means of the line source method. The range is 7.73 × 10 −4 ∼ 1.72 × 10 −2 cal/sec cm °C and it was noted that the thermal conductivity of unaltered rocks is greater than that of altered ones.