Chinoike Jigoku is called “blood pond hell” because of the red color of the water that emerges from the red clay. The red clay mud with iron oxide and magnesium oxide come out from the bottom of the pond and built up gradually for a long time. It’s the same as iron rust. Iron oxide and magnesium oxide naturally cause chemical reaction under high temperature and pressure. The water temperature of this pond is 78℃ (about 172℉).
In the Bungo Fudoki (description of a natural feature in Bungo/Oita area), it was described as “red hot spring” and the oldest natural Jiogku in Japan. It was discovered more than 1300 years ago after a volcanic explosion of Mt. Tsurumi occurred at that time. Some of other hells are said to have emerged around the same time.
Chinoike ointment, effective for skin diseases, is made from the red clay produced here.