| Abstract |
Calderas host abundant geothermal resources and are expected to be high potential areas of resource development for power generation. However, many calderas are covered by dense vegetation, making it difficult to directly observe ground surface conditions using satellite imagery. In this situation, vegetation activity, which is affected by geothermal-induced soil properties such as soil acidity and temperature, can be used for estimating geothermal system. Then, we aim to develop technology to detect new development potential areas by selecting the Sanzugawa Caldera in Yuzawa City, Akita Prefecture, north Japan as a case study field, through vegetation remote sensing and geomorphological analyses. For vegetation remote sensing, we employed hyperspectral HISUI data and applied a vegetation stress index to estimate the surface impacts of geothermal fluids. To validate these estimations, geomorphological analyses—such as assessments of elevation and slope variation—were conducted. These analyses confirmed that the detected vegetation anomalies were caused by geothermal activity. Furthermore, radon concentration measurements and resistivity surveys were carried out on-site. The integrated results suggest the presence of an impermeable layer in the middle caldera, which inhibits the ascent of geothermal fluids and causes a biased distribution of geothermal manifestations toward the caldera's periphery. This geothermal structure is interpreted to be a consequence of the caldera formation process. Similar caldera topographies are widespread in Japan, and the analytical flow presented in this study has the potential to contribute to the identification of new geothermal exploration targets. |