Tokachigawa Onsen has a gush of "mall hot water" that is rare in Japan.
In ancient times, plants such as reeds grew wild along the banks of the Tokachigawa River.
The hot spring water that gushes out through the lignite layer, which was formed by the sedimentation of these plants over a long period of time, is "mall water" that contains a lot of vegetable organic matter.
The word "mall" is derived from the German word for lignite.
While the temperature of hot springs in the center of the plains, such as in Obihiro City, is around 50°C (50°F), Tokachigawa Hot Springs are much hotter at 55-60°C (55-60°F), coming from 500-700 m below the ground.