Mount Chausu, Active volcano in Tochigi Prefecture, Japan.

Mount Chausu is a 1,915-meter stratovolcano in the Nasu range, built from lava flows, pyroclastic flows, a summit pyroclastic cone and a lava dome. Its upper slopes are bare brown and grey rock, with a shallow gully lined with lighter scree running down from the summit. Below, dense low vegetation covers the middle and lower slopes in patches of red, orange, yellow and green.

Activity began about 16,000 years ago with the Osawa pyroclastic flow. Later lava flows and the Oumaru pyroclastic group were followed by repeated steam eruptions. In the 15th century the Chausu lava dome flowed from a pyroclastic cone in the summit crater, completing the current form.

The mountain's slopes have long served as a base for mountain worship of the Nasu range, and the hot-spring town of Nasu-Yumoto below holds shrines such as Nasu Onsen Jinja near the Killing Stone, linked to the nine-tailed fox legend. At the summit stands the Nasu Take Jinja, the inner shrine of Nasu Onsen Jinja.

The Nasu Ropeway runs from Nasu Sanroku Station to Nasu Sancho Station near the summit, and the trail from the ropeway's upper station to the top is about 50 minutes. The only road access is Prefectural Route 17, which ends at Toge no Chaya and requires a U-turn, so traffic jams are common in peak season.

The summit crater holds a lava dome formed in the 15th century, when the mountain's activity began around 16,000 years ago. The Nasu Onsen Shrine's inner sanctuary, Nasu Take Shrine, stands at the top, and the trailhead below has a shrine to Yama no Kami, the mountain deity.