Utilization of volcano energy is an important subject in future geothermal energy development . Although extracting energy directly from crustal magma sources is an interesting subject, it may be more feasible to extract energy from shallow but hot fluid reservoirs which exist between surficial intense fumarolic activities and crustal magma sources in active volcanic geothermal systems in the initial stage of volcano energy development. Kuju volcano was chosen as a test site for the volcano

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... gy utilization experiment. Kuju volcano is situated in the Beppu-Shimabara volcanic graben in central Kyushu, Japan. It is a typical andesitic island arc volcano. The volcanic activity started about 0.3 Ma and in historic times, only phreatic explosions have occurred several times. An active solfatara field called Kuju-iwoyama in an explosive crater shows the most intense geothermal activity in central Kyushu . The natural heat discharge is estimated at about 100 MW, most of it from steaming ground and fumaroles . Temperatures