Japanese Alps

The Hida Range — the Northern Japan Alps — is not the wreckage of a continental collision like the European Alps. It is an island arc being squeezed. Japan sits above two subducting slabs, the Pacific and Philippine Sea plates, and the resulting east–west compression, working on a crust already softened by arc magmatism, has driven one of the fastest episodes of mountain-building on the planet: a wall of 3,000-metre peaks raised almost entirely within the Quaternary. The proof is written in granite. In 1992, Harayama reported in Geology that the Takidani Granodiorite — exposed in the gorge between Yarigatake and the Hotaka peaks — was about 1.4 million years old, the youngest exposed pluton then known on Earth. In 2013, Ito and colleagues (Scientific Reports) dated the nearby Kurobegawa Granite and found intrusive phases as young as about 0.8 million years — the youngest known exposed granite on the planet. Granite crystallizes kilometres underground; to be standing on it today, the range must have been uplifted and stripped of its cover at rates measured in millimetres per year, geologically sprinting. The Hotaka skyline tells the same story another way. The summits around Oku-Hotaka-dake (3,190 m, Japan's third-highest peak) are carved from the Hotaka Andesite: a welded-tuff sheet locally 1,500 m thick that filled an 18 × 6 km caldera formed by a colossal explosive eruption about 1.76 million years ago. Rock that erupted into a collapsing caldera — a hole in the ground — now forms some of the highest summits in Japan, hoisted skyward by the same uplift that exhumed the granites, then sharpened into arêtes and cirques by ice-age glaciers. And the ice is not entirely gone: in 2012 the Japanese Society of Snow and Ice recognized flowing ice bodies on Tsurugi and Tateyama — Gozenzawa, Sannomado and Komado — as Japan's first confirmed active glaciers (Fukui & Iida 2012). One volcano in the range is still working. Yakedake (2,455 m), rising directly above Kamikōchi, is the Northern Alps' only active volcano — one of Japan's 111 officially active volcanoes and among the 50 the Japan Meteorological Agency monitors around the clock. On 6 June 1915 it erupted from a kilometre-long fissure, and the resulting mudflow dammed the Azusa River to create Taishō Pond, with its ghost forest of drowned trees. Frequent phreatic eruptions followed through the 20th century, most recently in 1962–63, and a non-eruptive hydrothermal explosion near Nakanoyu killed four road workers on 11 February 1995. After a seismic swarm in January 2026 briefly pushed the alert to Level 2, JMA returned Yakedake to Volcanic Alert Level 1 ('potential for increased activity') on 4 March 2026 — a reminder that the steam on its summit is not decoration.