Hot springs and wells around the Yakedake volcano, Gifu, issue sodium bicarbonate-chloride waters, low in total dissolved solid. Isotopic data suggest that the most water is predominantly meteoric in origin, and that the water has not be appreciably altered by vapor loss in most of the hot springs and wells. Chemilcal and isotopic geothermometers indicate a reservoir temperature of 150°-200°C for most of the hot springs and wells.
Heat stored in hot rocks is estimated of Kurobe-Sennindani and Esan in the central and the northern Japan, respectively. Estimate is unsystematic and its success is rather lucky. For Kurobe-Sennindani the measurements were helpful of wall temperature, heat flow and heat conductivity on the rockwalls of the railway and the waterway tunnels penetrating through the central part of the hot rock. On the other hand, for Esan the geomagnetic survey and its analytical results by Nishida et al. (1974) provided the basic data to estimate heat stored in the hot rock. Heat discharges from the both hot rocks are evaluated as well as stored heat. The results show that stored heat and discharged heat of the both hot rocks are nearly comparative, 3 to 7×1015 cal and 2 to 6×1O5 cal/sec, respectively.
Alteration age has been estimated by the thermoluminescence(TL) of alteration minerals from Izu, central Japan, and Kuju, Kyushu. The alteration minerals applied to TL method are quartz, kaolinite, α-cristobalite, tridymite, and some mixtures of quartz, potash feldspar, alunite, sericite, kaolinite and montmorillonite. The ages for 16 altered samples are 0.15 to 2.62 Ma and are consistent with other geologic evidences. The results suggest that TL can be developed into a technique for dating of alteration minerals.
A basic study aimed at the extraction of the distribution of geothermally altered surface using Landsat computer compatible tape (CCT) has been done choosing Gochogake of the Hachimantai area, northern Japan as a model field. Spectral characteristics of pixels which represent typical geothermally altered flat surface without influence of vegetation were measured in terms of brightness value of CCT. However, the distribution of typical pixels is rare and it was felt that the necessity to set a category of geothermally altered surface + retarded vegetation for the purpose. The extraction of pixels included in this category is comparatively easy because most of geothermal areas develop in thick vegetated mountainous area and this brings strong spectral contrast between the target and the surrounding area. The application was made in the northern Kyushu area where large-scale geothermal exploration was being done. CCT used and described in this paper is the one which was taken on 22nd, Oct., 1973. Image analysis was done using IMAGE 100 system. Pre-processing such as geometric correction, UTM map conversion, and atmospheric correction was made before the analysis. The output was evaluated correlating the resemblance of distribution pattern of the categorized pixels with the existing alteration mapping data. Among the experiment, the case of the Garandake area where develops larger scale geothermal field and thus made possible the setting of better training area led better result.
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