Mountains · Tochigi
Mount Nantai
男体山なんたいさんNantai-sanThe sacred cone of Nikkō, rising from the shore of Lake Chūzenji.
Mount Nantai (男体山), 2,486 m, is the sacred volcano of Nikkō in Tochigi Prefecture, a symmetrical cone rising directly from the shore of Lake Chūzenji. The mountain is the object of worship of Futarasan Jinja, which has owned it since the monk Shōdō Shōnin first climbed it in 782; its ancient lava dam created both the lake and the Kegon Falls.
Overview
Mount Nantai dominates the Oku-Nikkō highlands: a steep, regular cone that climbs 1,200 m straight from the north-east shore of Lake Chūzenji. Its name, "male body mountain", pairs it with neighbouring Nyohō-san ("female peak") and Tarō-san ("son"); together they form the family of the three Futarasan deities.
The mountain is the shintai (sacred body) of Futarasan Jinja, one of the shrines of the Nikkō World Heritage site. The mountain lies within the shrine's own precinct, and the ascent begins by passing through the gate of its Chūgūshi on the lakeshore. Pilgrims and hikers climb it every summer; views extend over Lake Chūzenji, the Senjōgahara marsh and, on clear days, to Fuji.
Landscape and formation
Nantai-san is a young stratovolcano. Around 20,000 years ago its lava flows dammed the Daiya river valley, forming Lake Chūzenji; the lake's outflow now plunges 97 m over the lava cliff as the Kegon Falls. Later eruptions filled the valleys to the north with debris, creating the flat Senjōgahara and Odashirogahara, which evolved from lakes into marshes.
The summit crater is open to the north-west. A small eruption about 7,000 years ago was identified by research, which led to its listing as an active volcano.
Highlights
Summit shrine (Okumiya)
二荒山神社奥宮Futarasan Jinja OkumiyaThe inner shrine on the summit, with a large sword monument and a statue of the deity.
- 中禅寺湖Chūzenji-ko
A lake at about 1,270 m dammed by Nantai's lava, lined with former embassy villas.
- 華厳滝Kegon no Taki
A 97 m waterfall over the lava dam, the outflow of Lake Chūzenji.
Senjōgahara
戦場ヶ原SenjōgaharaA high marsh on former lake beds at the north-west foot, a Ramsar site with boardwalks.
Ecology
The mountain's flanks carry forests of Mongolian oak, fir and birch, with larch and dwarf trees near the summit. Senjōgahara at its foot is a highland marsh and grassland of national importance.
Flora
Mongolian oak
ミズナラmizunaraDominant in the forests of the lower slopes and around Senjōgahara.
Japanese azalea
レンゲツツジrenge-tsutsujiBlooms orange around Senjōgahara in June.
Fauna
Sika deer
ニホンジカnihonjikaAbundant in Oku-Nikkō; fences protect parts of Senjōgahara.
Asian black bear
ツキノワグマtsukinowagumaPresent in the forests; bear bells are commonly carried.
Culture
The Buddhist monk Shōdō Shōnin, founder of Nikkō's first temple, reached the summit in 782 after several failed attempts – the first recorded ascent of the mountain. Mountain worship of the three Futarasan deities developed around it, and Nikkō became one of the great centres of Shugendō before the Tokugawa shoguns built their mausolea there. Archaeological finds on the summit – mirrors, swords, coins and ritual objects – have been designated important cultural properties.
Futarasan Jinja Chūgūshi
二荒山神社中宮祠Futarasan Jinja ChūgūshiThe middle shrine on the lakeshore, gateway to the climbing route.
- 二荒山神社Futarasan Jinja
The main shrine in Nikkō town, a component of the World Heritage site.
Chūzenji temple
中禅寺ChūzenjiFounded by Shōdō Shōnin on the lakeshore, famous for its Tachiki Kannon carved from a standing tree.
History
c. 20,000 years ago
Lava flows from Nantai dam the valley and form Lake Chūzenji.
782
Shōdō Shōnin makes the first recorded ascent.
1934
Nikkō National Park is designated.
1999
The Shrines and Temples of Nikkō, including Futarasan Jinja, are inscribed as World Heritage.
2017
The Japan Meteorological Agency lists Nantai-san as an active volcano.
Through the seasons
Spring
Snow remains on the upper cone into May; the climbing season traditionally opens in early May.
Summer
The Tohai-sai pilgrimage festival from late July into early August; Senjōgahara flowers bloom.
Autumn
The flanks turn red and gold in early to mid-October, reflected in Lake Chūzenji.
Winter
The trail is closed; the snowy cone rises over the frozen shores of the lake.
Routes and trails
Chūgūshi route
From Futarasan Jinja Chūgūshi straight up the south-east flank: about 3.5–4 hours up, 2.5 hours down. Steep and physically demanding but non-technical.
Shizu route
From Shizu pass on the north side, a shorter but rougher ascent; its access road and trail may be closed after storm damage.
Senjōgahara nature trail
A flat boardwalk walk of 2–3 hours at the foot of the mountain, from Akanuma to Yumoto; easy.
Practical notes
- The climbing season and the climbing offering are set by Futarasan Jinja; check the shrine's notices before going.
- Lake Chūzenji is reached by bus from Tōbu-Nikkō and JR Nikkō stations up the Irohazaka hairpin road, about 45 minutes.
- Carry sufficient water – there is none on the route – and be prepared for strong wind on the summit.
- Nantai-san is monitored as an active volcano; current information is published by the Japan Meteorological Agency.
Frequently asked questions
How long does it take to climb Mount Nantai?
From the Futarasan Jinja Chūgūshi on Lake Chūzenji the ascent takes about 3.5–4 hours for some 1,200 m of height gain, and the descent about 2.5 hours. The path is steep and straight, with loose volcanic rock in the upper part.
When is Mount Nantai open?
The trail passes through the shrine's gate and is open during the shrine's summer climbing season, traditionally from early May to late October. Opening days and the climbing offering are set by Futarasan Jinja.
Why is Nantai-san classed as an active volcano?
Research showed that it erupted about 7,000 years ago, within the 10,000-year criterion, and the Japan Meteorological Agency added it to its list of active volcanoes in 2017.
What is the Tohai-sai?
The summer climbing festival of Futarasan Jinja, held from late July into early August, when pilgrims climb through the night to greet the sunrise on the summit.
Related
Sources
- 1.日本の主な山岳標高 (opens in a new tab) — 国土地理院 (Geospatial Information Authority of Japan)
- 2.日光国立公園 (opens in a new tab) — 環境省 (Ministry of the Environment)
- 3.活火山（男体山） (opens in a new tab) — 気象庁 (Japan Meteorological Agency)
- 4.栃木県公式ホームページ (opens in a new tab) — 栃木県 (Tochigi Prefecture)