Nantaisan stratovolcano rises above the north shore of Lake Chuzenji in Nikko National Park, and forms a backdrop to the temple complex there. Lava flows from the early stage of edifice construction dammed the Daiyo River, forming Lake Chuzenji; the Kegon waterfall plunges over this barrier. Nantaisan has an asymmetrical profile when viewed from the west as a result of late-stage collapse on the north side. Two major late-stage eruptions ejected large amounts of scoria, followed by the emission of pyroclastic flows. The latest effusive activity produced the Osawa lava flow, a thick, viscous dacitic flow that traveled from the breached crater down the N flank. The Bentengawara pyroclastic-flow deposit, representing the latest known eruptive activity, was radiocarbon dated at about 10,000 years Before Present and was emplaced following a quiescent period of about 3,000 years.