The Yokoyu-river flowing in the Jigokudani has its source in the Onuma-ike of the Shiga-kogen. It runs down to the Japan Sea with joining several mountain streams and with changing the name from Yamase-river to Chikuma-river and to Shinano-river.
The eye-catching scenery in the Jigokudani is steep cliffs and piled sharp angular rocks.
The geological layer is comprised of quarts diorite. There are some rifts made by crustal movement or by magma which has firmed up after long-term cool down.
The rocks crumble and become angular by disintegration. The onsen of Jigokudani springs out from the layers of quartz diorite.
The layers of quartz diorite
The Jigokudani fountain of Shibu is a national monument. According to a literature, the fountain, which is constantly erupting hot water of 100 degrees centigrade, temporally stopped in 1783 because of the explosion of Mt Asama.
The phenomenon of erupting hot water by volcanic activities is called ‘Hell (Jigoku)-phenomenon’ in terms of earth science. It might be the reason that we call this place ‘Jigokudani’. The onsen in Jigokudani area uses the hot water erupting naturally from the riverbed of Yokoyu-river. The water, which is salt spring and crystal clear, supplies to Shibu-onsen and Kanbayashi-onsen. Korakukan, opened in 1864, is a historical therapeutic bath facility here.