Mount Yake

Taisho Pond, the flooded forest most people photograph on their way into Kamikochi, is this mountain's doing. On June 6, 1915, an eruption of Mount Yake sent a mudflow across the Azusa River and dammed it. The volcano has not gone quiet since. A steam explosion in 1962 crushed the old summit hut and injured four people, and the Japan Meteorological Agency watches it around the clock and publishes an eruption alert level. At Level 1 you can climb to the north peak, 2,444 m, where steam hisses out of sulfur-stained vents a few steps from the path; when earthquakes pick up the level can go to 2, which closes the ground around the crater. The south peak, 2,455 m and the true high point, is off-limits because its rock keeps collapsing. Two trails do most of the work. From Kamikochi you start near Tashiro Bridge and climb to Shin-Nakao Pass, with ladders on the way; the Nakanoyu side starts from Route 158 on the road up to Kamikochi. Kamikochi's tourism site rates the hike at 6.4 km and about 5.5 hours. JMA asks climbers to wear a helmet and not to linger by the vents, where gas can burst out without warning. The trail is closed in winter.