This high altitude lake was formed about 20,000 from the damming by a volcanic eruption. Humans started building shrines in the area about 1200 years ago. The main volcano (Mt. Nantai) is still considered active – and it was odd to look around and see so many volcanic craters surrounding us during the boat ride around the lake. I could also see the paths of recent lahars, and geomorphic contours clearly indicated locations of the next constructions to succumb to gravity.