The Water in Kikuchi Gorge
Countless streams that originate in the mountains around Kikuchi Gorge converge above here to form the Kikuchi River. The water in the gorge is clear and cold, typical of secluded rivers at high altitudes. What makes it distinctive is its almost complete lack of active volcanic chemicals and its low magnesium and calcium content.
The Kikuchi River takes shape over 800 meters above sea level, relatively close to the top of the mountains that form the northwestern part of the Mt. Aso caldera’s outer rim. The river’s sources are all on the outer slope of the caldera, and are also situated at an altitude significantly higher than the caldera floor. Consequently, chemicals derived from the active volcano are unable to enter the Kikuchi watershed. The water is, however, filtered by layers of the ancient volcanic rock that form the caldera walls. This combination of geography and geology result in the pure, soft water for which Kikuchi Gorge is famed.
The interplay of clear, low-mineral water and volcanic rock in the gorge also affects the river’s appearance. In places where the riverbed consists of light rock, the water appears cobalt blue—caused by sunlight passing through it and reflecting off the rock without interference from substances in the water.