Geothermal Features of Yamagata Prefecture, Northeast Japan

Abstract

The Yamagata prefecture, located in northeast Japan, has about 140 hot spring areas. The area is underlain by pre-Tertiary basement rocks, Tertiary formations, Pliocene to Pleistocene deposits, and Quaternary volcanoes. Typical Quaternary volcanoes are Funagata, Zao and Azuma in the Ou Mountains, and Chokai, Gassan, Hayama, and Hijiori in the Uetsu Mountains. Geothermal resources related to Quaternary volcanoes such as Azuma, Zao, and Hijiori areas are accompanied by high temperature hot springs associated with hydrothermal alteration zones on the surface. In Azuma and Hijiori areas, maximum temperatures of the exploration wells reach above 200 oC. Hijiori and Akakura areas related with caldera are accompanied by high temperature thermal waters. Meanwhile many non-volcanic hot springs are scattered mainly along the Yonezawa Basin and the Yamagata Basin. Some of the high temperature hot springs such as Akayu, Kaminoyama, Tendo and Higashine are situated on the margins of these basins or in volcano-tectonic depressions, which are suitable structures for thermal waters reservoirs.