Ata Caldera - Unagi Crater, Yamagawa Geothermal Power Station

Mt Kaimon (Kaimondake)	Scientists monitoring fumarole emissions, Unagi Village

The Ata Caldera is the result of the eruption of a massive "supervolcano" about 105,000-110,000 years ago. The caldera forms the bottom section of Kagoshima Bay and also the SE tip of Satsuma Peninsula. It lies approximately 40km south of the Aira Caldera in which the present-day Sakurajima volcano is active. Within the perimeter of Ata Caldera are numerous more recent volcanic features. Most prominent is Mt Kaimon (922m) in the western corner of the caldera which covered the entire peninsula in scoria about 4000 years ago. The volcano was most recently active in 884-885 and it is possibly at this time that the small andesitic lava dome found in the summit crater was formed. About 5000 years ago, the 4x3km Ikeda Caldera was formed in the NW corner of Ata Caldera by a powerful explosive eruption. A series of further craters were formed to the SE of Ikeda Caldera and were probably the results of eruptions triggered by intrusions of dikes from fissures extending in this direction from Ikeda. These craters are Narikawa, Unagi, Ikezoko and Matsugakubo.

Unagi Lake / Village

On the northeast shore of Unagi lake is a small area containing high temperature hot springs / fumaroles. This area has been chosen as the site of Unagi village which benefits from the springs in several ways. On the one hand, as at most Japanese geothermal sites a bathhouse has been established, on the other many of the fumaroles have been "tapped" in order to use the steam emitted for heating greenhouses or for cooking sweet potatoes. In the latter case, these are placed between several layers of cloth which are lain over fumaroles that have been encased in simple concrete structures. This provides for a significant-sized steam cooker. Since the fumarolic gases contain very low levels of sulphurous compounds the potatoes remain neutral in taste. Unagi actually has the only major non-saline hot springs in the area.

Lake Unagi	Unagi Village

Workers cooking sweet potatoes using fumarole gases	Sweet potatoes on fumarole cooker

Workers cooking sweet potatoes using fumarole gases	Workers cooking sweet potatoes using fumarole gases

Yamagawa Geothermal Power Station

The Yamagawa Geothermal Power Station began operation in 1995 and was producing about 30MW at this time. The Fushime geothermal field in which the power station is located has been under exploration since the late 1970s by Japan Petrolium Exploration Co. Ltd (JAPEX) and its subsidiaries. The power station lies near the coast covering an area of 160,000 square meters, whilst many of the wells have been drilled outwards from the site, so that it draws energy from a much wider area. In 2000, 12 production wells (1500-2500m deep) and 4 reinjection wells (800-1300m deep) were in operation (Okada et al. 2000, Geothermics 29, p.279-311). Approx. 225 tonnes / hour of steam are processed into energy and 350 t/h of hot water are reinjected.

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Power station with Takeyama peaks in background	Power station with Takeyama peaks in background

Power station with geothermally heated greenhouses in foreground	Power station machinery

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