2022 Volume 131 Issue 6 Pages Cover06_01-Cover06_02
In the western half of the Ata caldera, located at the mouth of Kagoshima Bay, topographic landscapes related to volcanic activity after the Pleistocene epoch of the Quaternary, such as the crater lakes of Lake Ikeda and Unagi pond, can be observed. Hot springs and steaming fields, represented by Ibusuki hot spring, are also distributed in this area. The photo shows boiling water issuing at a sand beach in the Fushime hydrothermal area, which can be observed only at low tide. The adjacent cliff, comprising Ikeda pyroclastic sediments, was formed 6300 BP when Lake Ikeda erupted (Kawabe and Sakaguchi, 2005). Various studies have been done related to development of the Yamagawa geothermal plant in the Fushime area, where hydrothermal water at 330°C was recovered from a depth of 2000 m (e.g., Yoshimura and Ito, 1994). Primary hydrothermal water in this area was formed through a reaction with seawater at that temperature, and its water chemistry was changed during the ascending path by dilution with subareal fresh groundwater and subsequent mineral precipitation (e.g., Okada et al., 2000). Located near the hot spring are municipal public and sand steam baths, as well as an abandoned salt field, where hot spring water was used to make table salt through condensation. Behind the issuing hot spring can be seen Mount Kaimon volcano, which last erupted in 885 AD. This area is one of the best for experiencing the reality of active volcanoes and geothermal energy, and for undertaking research on geology and geochemistry.
(Photograph & Explanation: Harue MASUDA)