Geothermal Resource Exploration by Stream pH Mapping in Mutsu Hiuchi Dake Volcano, Japan

[...]the overlying stream waters would be unaffected by the volcanic gases, and would instead retain the neutral state of surface water originating from rainwater and shallow groundwater, as it flows in from its vicinity, which appears as abnormal areas in terms of higher pH levels in contrast to the general trend observed in the area. Shimada [23] previously pointed out that, in areas where rising volcanic gases are identified, there is almost no chance of finding a geothermal reservoir deep underground because the voluminous hot water reservoir tends to feed the rising volcanic gases [23]. [...]the pH distribution map for stream water within the Mutsu Hiuchi Dake geothermal field might indicate the possibility that the Mutsu Hiuchi Dake East Slope Fault has formed a neutral, mature hydrothermal system underground. Permeable bodies usually consist of faults, but columnar jointed sheets and dikes as well as fractured formations may also play a role in reservoirs. [...]these findings indicate that mapping the distribution of stream and spring water pH in a geothermal field could help to identify geothermal reservoirs containing neutral, high-temperature water suitable for geothermal development. [...]as a new geothermal exploration technique, the mapping of stream and spring water pH distribution would likely contribute to the promotion of geothermal development in inaccessible and remote regions. 6.