Kame-ana (Potholes)
This geological phenomenon can be found in the Shiryu upriver section of the Ryuokyo Valley, where the rocks are mostly andesite, created during the early stages of the volcanic eruption 22 million years ago. Scattered across the horizontal rock terrace are circular holes, formed by friction-induced erosion as circulating water rubs small rocks or pebbles against the larger rock’s surface. These holes are called kame-ana, literally “pot holes,” for their resemblance to large pots or kettles. Similar holes have been found in the rhyolite rocks downriver, but those are situated much higher in the cliff walls, whereas the holes here are only 1 meter above the current water level. The difference is believed to be due to the river current eroding the rock downstream at a faster pace than in this section of the gorge.