Mount Nasu, Volcanic complex in Tochigi Prefecture, Japan

Mount Nasu forms a group of five peaks in northeastern Honshu and sits within a large protected area of forest and open highland terrain. The landscape shifts between wooded slopes and barren zones near the craters, where sulfur vapors rise from the ground and vegetation remains sparse.

Nasu's volcanoes began erupting about 600,000 years ago, starting at Kashi-Asahi Peak in the north; Sanbonyari followed 400,000 to 250,000 years ago, then Asahi and Minamigatsusan from 200,000 to 50,000 years ago. Chausu, active for the past 30,000 years, erupts only andesite lava and has grown into a rounded lava dome. Recorded eruptions from 1408 to 1410 formed that dome and sent pyroclastic flows that killed more than 180 people; since then only small steam eruptions and earthquake swarms have occurred.

Mount Nasu is listed among Kyuya Fukada's 100 Famous Japanese Mountains. Each May an opening ceremony (kaizan-sai) marks the start of the climbing season, and each November a closing ceremony (heizan-sai) ends it. The mountain's name is used both for the whole Nasu range and, more narrowly, for its main peak, Chausu-dake.

The trailhead is at Toge-no-chaya (1,462 m), reached by road via the Nasu Highland Line; general cars stop at its car park, and the bus stop at the ropeway's base station is about a 20-minute walk away. The Nasu Ropeway runs from the 7th to the 9th station in roughly four minutes, leaving under an hour to the Chausu summit. Temperatures near the top are about 10°C lower than on the plain, and the ropeway halts in strong wind or thunderstorms, so carry water and wear walking shoes in case you must descend on foot.

Sanbonyari Peak is the highest point in the group and rises to 1,917 meters (6,289 feet), though it holds no active crater. Only Chausu Peak continues to show volcanic activity with visible gas vents along the crater rim.