Hydrogen produced by the water-splitting reaction is one of the alternate sources derived from fossil fuels. However, the present systems for the hydrogen production still require the extra energy or processes such as heating, milling and adding the chemical agent. The hot springs in Japan are naturally in high temperature and in wide range of pH. We investigated the combination of hot spring water and waste aluminum that are appropriate for hydrogen production without extra energy. Here, we used waste aluminum for reducer of water-splitting reactor. The hydrogen production system in Onsen (hot spring) area has a potential to promote not only the environmental and energy problems but also the activation of the local community as the system of “local production for local consumption”. In this study, the effects of the characters of hot springs and the conditions of the hydrogen generator system were revealed by the laboratory experiments. The water-splitting reaction was enhanced by using the hot spring water of (1) lower pH (< 2), (2) higher temperature, and (3) higher ratio of HCl/H₂SO₄. The concentration of cations in the fluid is not related to the reaction rate of hydrogen production. The prototype of the hydrogen generator for the water splitting reaction by using the acidic hot spring water and waste aluminum was developed and used in two type systems: batch and flow-through. The laboratory experiment by using the original generator revealed that hydrogen production was more efficient in the flow-through system because of constant pH value of fluid.

In order to evaluate the present geothermal resources in fossil volcanic caldera systems, petrological structures under calderas were investigated and compared with geophysical structures for Shirasawa Caldera (10-8 Ma) and overlying Jogi Caldera (7 Ma), Sendai, NE Japan. The petrological composition, depth, and evolution of the caldera-forming magmas were constrained by the analysis of melt inclusions in quartz crystals from volcanic ejecta of the calderas. The major and trace element compositions of the melt inclusions in the Shirasawa and Jogi Calderas are similar, and classified as low-alkaline tholeiitic dacite-rhyolite, with noticeable variations in Na₂O and K₂O contents among the formations. The SiO₂ and K₂O contents of the melt inclusions suggest the depth of generation of the magma is approximately 10-20 km. The compositions of melt inclusions on the Qtz-Ab-Or system form a fractional trend of plagioclase, with some samples showing fractional trends of both plagioclase and quartz. The trace element compositions of the Shirasawa and Jogi Calderas are depleted in Sr and Eu, suggesting the fractionation of plagioclase. The melt entrapment pressure is estimated on the basis of the pressure dependency of the eutectic composition between Qtz-Ab, and it concentrates on 30-300 MPa, suggesting that the depth of entrapment is 1-11 km. These ranges of entrapment pressure indicate that magma chambers had existed 1-11 km under the calderas. The H₂O contents in the melt inclusions are 4 wt% on average, showing that the most of the melt in the magma chambers was saturated with H₂O.

These results suggest that the caldera-forming magma was generated at a depth of 10-20 km, and magma chambers were formed at 1-11 km due to gravitational equilibria. Subsequent fractionation of plagioclase and quartz led the release of volatiles, which promoted eruptions and formed the Shirasawa Caldera. It is expected that the fluids in the melt were liberated during the ascent and cooling of the magma chambers, and were trapped at depth, which can be detected by the present geophysical observations.

The locations and depth of the ancient magma chambers (1-11 km) coincides with that of the fluid distributions estimated from present seismic observations (i.e., low velocity zones; 0-10 km), suggesting that the remnants of the magma chambers act as fluid reservoir. Seismic clusters at a depth of 8-13 km under the Shirasawa Caldera suggest that the fluids are still active. The depth of 2-5 km — which is the peak of the entrapment depth of the melt inclusions — coincides with seismic reflectors, and abundant fluid is expected at 2-5 km depth under the Shirasawa Caldera.

In Ground Source Heat Pump (GSHP) systems, reduction of initial and running costs are important. Previous studies show that groundwater flow around the well would enhance heat exchange performance and is expected to reduce initial costs and running costs of GSHP systems. Either water injection into or pumping from the heat exchange well induce flow of water in the well and the flow may enhance heat exchange performance. In Akita University, Japan, Thermal Response Tests (TRT), a common method to determine effective thermal conductivity of ground and thermal resistance of borehole. These basic parameters are necessary to study heat transfer mechanism and to design sustainable closed GSHP systems. Some researchers reported that are effective to improve BHE characteristics. In this research, a numerical model of heat exchange well drilled in Akita University was developed and numerical simulations were carried out for the modeling of TRTs either with water injection or water pumping case. In addition, characteristics of the system were investigated through numerical simulations.