Onneto Yunotaki Falls

Thermal waterfall on the western slope of Mt. Meakan, where lava from an eruption 7,000 years ago now fractures to release geothermally heated water. It is the only known place on land where the natural production of manganese oxide can be observed, a process that normally occurs only in the deep ocean. Cyanobacteria in the warm water produce oxygen through photosynthesis, which reacts with manganese ions carried up from the lava to form the compound at a rate of about one ton per year. The site is within Akan-Mashu National Park and can be reached on foot from the Onneto lakeside area.