At present, we are using heat in the form of volcanic steam from dormant volcanoes in Japan for electric power generation.

However, in due time it will be possible to make use of the heat, itself, from present volcanoes. For this, necessary techniques must be developed. Heat from the Cenozoic granitic rocks also may be utilized.

At the beginning of the Miocene, Japan seems to have entered into a new geologic evolution. Depression, violent volcanism, and some igneous intrusion took place rather abruptly on the land, and the Miocene sea began to transgress and finally covered almost all of Japan. The deep depression of Fossa Magna formed and separated northeast Japan from southwest Japan. In the Pleistocene, the sea largely regressed, but volcanism continued until the present, and has constructed many volcanic cones and lava plateaus.

The writers are calculating the heat generated by each stage of the igneous activity. Ages and heat of subterranean heat sources can be learned from analysis of heat-flow-profile data utilizing the method of differences of running-mean-values, which acts as a kind of filter for different wavelengths. The long wavelength corresponds to a large-scale source of heat, probably started during very ancient time, whereas the middle wavelength corresponds to a middle-scale source, probably started later than the first one, and very short wavelength expresses the heat flow caused by a smaller, very young heat source.

The method has been applied in a preliminary manner to the present study, and some significant correlation with past igneous activity can be demonstrated. Finally, the geothermal energy, which will be available now for use in Japan, is being calculated.

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