Isotopic and chemical features of hot springs in Akita Prefecture

All over the Akita Prefecture, many hot springs are located. Most of them are of meteoric water, fossil sea water and volcanic gas origins. In the Ohdate-Kazuno area, moderate temperature hot springs of meteoric water origin are found, which may exist as rather shallow formation water in the Green Tuff formations. On the contrary, high temperature geothermal waters of meteoric origin, which are used for power generation, are obtained in two volcanic area of Hachimantai and Oyasu. Those geothermal waters are expected to come up through vertical fissures from depth deeper than 2 km. The difference of these two manners of meteoric water circulation should be necessarily explained to understand the relationship of shallow and deep geothermal systems. About some hot springs of fossil sea water origin, the relationships of δ D and Cl- don't agree to the mixing relation of sea water and meteoric water. This may be explained by two different processes, one of which is mixing of sea water with saline meteoric water (Cl- ca. 12 g/kg). The other is modification of δD by hydrogen isotopic exchange with hydrous minerals underground, or by exchange with atmospheric vapor during a relic lake before burying. (author)