Mount Fuji

Mount Fuji was made by volcanoes, one on top of another.

First came an old volcano. A newer one grew over it. Then the newest one covered them both. Its lava made the smooth shape we see today.

Mount Fuji is a stratovolcano, a volcano built from many layers of lava and ash. The mountain we see is really three volcanoes stacked together. At the bottom is the oldest, Komitake. About 100,000 years ago a new volcano, Ko Fuji (Old Fuji), grew on top of it, and its lava and ash covered most of Komitake.

The newest, Shin Fuji (New Fuji), became active about 10,000 years ago. Its lava and ash filled in the slopes of the older volcanoes and built the summit, giving Fuji its smooth, nearly perfect cone. Japan sits where plates of the Earth's crust meet, and geologists link Fuji's eruptions to one plate sinking beneath another off Japan's southern coast.

Britannica notes that Fuji's age is disputed: it seems to have formed during the past 2.6 million years on a base up to 65 million years old, with the first eruptions probably after 700,000 years ago and the present stratovolcano rising after about 400,000 years ago between Komitake and Ashitaka-yama. Ko Fuji surmounted Komitake about 100,000 years ago, and Shin Fuji probably became active about 10,000 years ago, filling the slopes of its predecessors and adding the summit zone.

Fuji belongs to the Fuji Volcanic Zone, a chain running north from the Mariana and Izu Islands through the Izu Peninsula to northern Honshu. Geologists cited by Britannica link its activity to subduction at the Nankai Trough along Japan's southern coast. Large eruptions occur about every 500 years; the volcano has erupted more than 15 times since 781, and the last major eruption, in December 1707, followed a magnitude-8.4 earthquake by 49 days. Activity since has been limited mostly to small earthquakes.

Forests grow on the lower slopes of Mount Fuji.

Higher up, there is mostly rock and ash. Five pretty lakes lie on its north side. On calm days, Fuji shines upside down in the water.

Life on Mount Fuji changes with height. The lower slopes are covered in forest. Higher up, above the tree line, the mountain is mostly bare volcanic rock and ash, with only a few plants. At the top, conditions are alpine: the average temperature is about −19 °C in winter and only about 7 °C in summer.

On the northern side lie the Fuji Five Lakes, made when lava flows dammed valleys. Lake Kawaguchi is famous for the upside-down reflection of the mountain on its still water. Lava flows also left fragile shapes called lava tree molds. In recent years the tree line has moved higher and summit temperatures have risen, changes Britannica links to a changing climate.

Britannica describes conditions varying sharply with elevation: forested lower slopes, and above the forest line a largely barren mountain of volcanic rock and ash with sparse vegetation. The base has a temperate to subtropical climate; the summit is alpine, averaging about −19 °C in winter and 6.8 °C in summer, with about 2,272 mm of precipitation a year, mostly in summer. UNESCO records that pilgrims recognized three zones on the way up: grass around the base, a forest area, and the burnt or bald mountain of the summit.

The Fuji Five Lakes, Yamanaka, Kawaguchi, Sai, Shōji and Motosu, were formed by lava damming; Kawaguchi, the lowest at 831 m, is noted for its reflection of the mountain. UNESCO lists lava tree molds, springs and waterfalls among the inscribed natural features. Britannica links an upward shift of the tree line and rising summit temperatures to changing climate, and the official climbing site calls the mountain's ecosystem precious, asking climbers not to bring in seeds of plants from other mountains.

People can climb Mount Fuji only in summer.

It can be very cold and windy at the top, even then. Climbers wear warm clothes and good boots. They take all their rubbish home, because there are no bins on the mountain.

Mount Fuji is open for climbing only during a short summer season; in 2026 its trails opened on 1 or 10 July, depending on the trail, and closed on 10 September. Outside the season all trails to the summit are closed, because snow, ice and strong winds make climbing dangerous, and mountain huts and first-aid stations close.

Even in summer, the summit can drop to near 0 °C before sunrise, and storms can blow up suddenly, so climbers need boots, rain gear and warm clothes. The official climbing site asks everyone to take all their trash home, since there are no trash cans on the trails or in the huts. Do not take stones or plants, never write on rocks, and brush seeds off your boots so you do not bring plants from other mountains.

The official Mt. Fuji climbing website, run by the Council for the Promotion of Appropriate Use of Mt. Fuji, says climbing is possible only during the summer season, on four trails (Yoshida, Subashiri, Gotemba and Fujinomiya); in 2026 the Yoshida and Subashiri trails opened on 1 July, the Gotemba and Fujinomiya trails on 10 July, and all closed on 10 September, and outside the season all summit trails are closed and climbing is extremely dangerous, with huts, first-aid centers and phone coverage unavailable and severe weather likely.

It warns of fierce winds, temperatures falling about 0.6 °C for every 100 m of height, near-freezing summits before sunrise even in summer, and sudden summer thunderstorms, and lists hiking boots, rain gear, cold-weather clothing and a helmet (for falling rocks and volcanic eruptions). Its rules: take all trash home, as there are no bins; do not take or move stones; no graffiti; no capturing, collecting or damaging plants and animals; protect fragile lava tree molds; and remove seeds from boots so as not to introduce non-native plants.