Mount Nantai

Nantaisan stratovolcano rises above the north shore of Lake Chuzenji in Nikko National Park. Lava flows from the early stage of edifice construction dammed the Daiyo River, forming Lake Chuzenji; the Kegon waterfall plunges over this barrier. A late-stage collapse occurred 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.