On the south side of Mt. Tokachidake Hot Spring, Kokonoe Waterfall flows up from Sampozan Valley.

This waterfall flows over rock formations formed from lava, during a volcanic eruption which occurred 250 thousand years ago.

Cracks, known as ‘joints,’ have formed here and there in the surface of the rock, and then gradually flattened over time. The water from the waterfall flows over the resultant flat surfaces.

These stony surfaces are formed from a type of rock known as ‘dacite.’

Because the mountains of the Tokachidake Mountain Range are made mostly of andesite and basalt, the dacite which can be seen at Kokonoe Waterfall is quite rare (The peak of Mt. Tokachidake is also made of dacite). Mt. Usu and Mt. Unzen-Fugendake, located in other parts of Japan, are also composed of dacite.

Dacite is a volcanic rock which includes a large amount of silicon dioxide (SiO2 ,60-70%). This likely means that only magma containing large amounts of silicon dioxide can form dacite.