Mt. Fuji Primeval Forest and Aokigahara Sea of Trees
The forests on the northwestern flanks of Mt. Fuji carry one of the longer designation histories among Japan's natural monuments. The original protection order, issued on February 24, 1926, covered three high-altitude woodland zones (Omuro, Yumiizuka, and Oniwa-Okuniwa) linked by the Fuji forest road. More than eighty years later, on March 8, 2010, the designation was extended downslope to include Aokigahara Jukai, the dense conifer woodland that has grown over the lava field of the great Jōgan eruption of 864 AD. The combined property is registered today under criterion (ii): a representative primeval forest with a rare assemblage of forest plant species.
What makes the site geologically and biologically uncommon is the contrast it preserves. Within a single protected zone, visitors walk through an old broadleaf forest that the volcano never burned, then descend onto a 1,200-year-old forest growing directly on cooled basalt. Few places in Japan let you read forest succession on a single afternoon's walk.
The Original 1926 Designation
The first protection order drew on Bunzō Hayata's 1911 botanical survey, The Vegetation of Mt. Fuji, which mapped the vertical zoning of plant life on the volcano. The 1926 documentation describes the protected woodland as extending roughly four ri (about 16 kilometers) along the mountain's flank, and identifies three distinct character zones.
Omuro Primeval Forest, on the lower slopes around Mt. Ōmuro, is a deciduous broadleaf woodland that the volcano spared because the Jōgan lava flowed around the older parasitic cone rather than over it. Beech (buna), uncommon on the rest of Mt. Fuji, grows here at scattered intervals, and a sharp visual edge separates this older woodland from the surrounding conifers. Yumiizuka Forest, higher up, is a mixed conifer-broadleaf belt. Oniwa and Okuniwa, near the fifth station at around 2,300 meters, are dwarf conifer woods: twisted Tsuga diversifolia and Japanese larch bent by wind and snow, growing among scattered scoria cones. Stone-paved walking paths and the Ochūdō pilgrimage route trace this upper zone.
The Jōgan Eruption and the Birth of Aokigahara
The lava that built Aokigahara erupted between June 864 and 866 AD, recorded in the Heian-era chronicle Nihon Sandai Jitsuroku. The eruption opened a fissure on the northwestern flank, at about the first to second station of the present Shōji climbing route, and built a row of small scoria cones. The largest of these was Mt. Nagao. Estimates place the total ejected volume at roughly 1.4 billion cubic meters.
The flow advanced for more than two months, splitting around Mt. Ōmuro and burying the broad montane forest below. At the foot of the mountain it ran into Lake Senoumi, an inland water body of perhaps 100 meters at its deepest point, and filled most of it in. The two narrow lakes that remain on either side of the buried basin, Lake Saiko and Lake Shōji, are remnants. Drilling surveys carried out in recent decades have confirmed that they share a single ancient lakebed beneath the lava.
After the lava cooled, mosses colonized the porous rock, then ferns, then trees. The forest visible today, roughly 1,200 years on, is the result. The protected zone covers about 30 square kilometers between elevations of 920 and 1,300 meters.
A Forest Growing on Rock
Tsuga (Japanese hemlock) and hinoki (Japanese cypress) dominate the canopy, joined by harimomi spruce, Japanese white pine, Japanese red pine, and the broadleaved Quercus crispula. Local guides estimate the oldest standing trees at 330 to 360 years. By altitude alone, this zone would normally support deciduous broadleaf species; the lava substrate retains little water and almost no soil, conditions that favor shallow-rooted conifers.
The most striking ecological detail is at ground level. Tree roots cannot push into solid basalt, so they spread sideways and grow above the rock—gnarled and exposed, gripping the surface like the fingers of a hand. After heavy rain, the forest goes quiet in a particular way: the porous lava drains everything away, and there are no streams to murmur.
Lava Caves and Lava Tree Molds
When the Jōgan flow ran through the older forest, it engulfed standing trees and cooled around them. The wood burned out, leaving hollow shafts in the rock called lava tree molds. Twelve of these in Narusawa village, along National Route 139, are protected as a Special Natural Monument; the largest measures 1.8 meters across and 4.6 meters deep.
Three lava caves within the forest are publicly accessible. Fugaku Wind Cave (Fugaku Fūketsu), a 201-meter horizontal tunnel with a vault reaching 8.7 meters, maintains an interior temperature of about 3°C year round. Until the early Showa era, silkworm eggs were stored here for cool incubation. Narusawa Ice Cave (Narusawa Hyōketsu), a 153-meter ring-shaped vertical cave designated separately as a Natural Monument in 1929, holds ice columns into late spring. Saiko Bat Cave (Saiko Kōmori-ana), at about 350 meters the longest open to visitors, is named for the bat colonies that once wintered there.
Walking the Forest
Two short walking routes through Aokigahara are recommended for first-time visitors. The Tōkai Nature Trail between Fugaku Wind Cave and Narusawa Ice Cave takes about thirty minutes one way and stays on a wide, well-marked path. A longer route runs between the Saiko Wild Bird Forest Park and Saiko Bat Cave, about forty minutes. Both routes pass over exposed lava, raised roots, and moss-covered boulders.
The two warnings repeated by local guides are worth attending to. First, the lava ground under the forest litter is uneven and full of small drops; turning an ankle off the trail is the most common accident. Second, the entire protected area is regulated under both the Cultural Property Protection Act and the Natural Parks Act, so removing rocks, plants, or wood is prohibited, and several arrests have been made over the years for taking lava away.
For panoramic views without entering the forest itself, the observation points at Kōyōdai and Sanko-dai look down on the canopy as one continuous green expanse, with Mt. Fuji rising directly behind. The view explains the name: from above, the forest looks like a sea, its surface rippling in the wind.
Around the Protected Area
The Fuji Five Lakes rim the northern foot of the mountain, and three of them, Lake Saiko, Lake Shōji, and Lake Motosu, share their edges with the lava field. Lake Saiko's western shore offers a thatched-roof village reconstruction at Iyashi-no-Sato Nemba, and the Saiko Wild Bird Forest Park nearby tracks more than 200 bird species. Lake Shōji is the smallest of the five lakes and offers some of the clearest mirror-image views of Mt. Fuji. Higher up the mountain, the Fuji Subaru Line ends at the fifth station, from which a short walk reaches the Oniwa-Okuniwa woodland, part of the same designated property but a different world from the dense lowland forest.
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Q&A
- Can visitors enter Aokigahara without a guide?
- Yes. The marked walking paths between Fugaku Wind Cave, Narusawa Ice Cave, and Saiko Bat Cave are open to anyone without restriction. For walks beyond these main paths, a licensed nature guide from Fujikawaguchiko Town's accredited list is recommended; the forest looks the same in every direction once off the trail, and visual landmarks are scarce.
- When is the best season to visit?
- The conifer canopy is evergreen, so the forest looks broadly similar through the year. Late spring brings new growth and the ghost-white parasitic plant ginryōsō (Monotropastrum humile) in shaded patches. Summer keeps the interior cool, and the caves stay near freezing. Late October to early November lights up the broadleaf belt at Mt. Ōmuro and the lookout points at Kōyōdai.
- Is the forest part of the World Heritage site?
- Yes. Aokigahara and the surrounding primeval forest are part of the Mount Fuji World Cultural Heritage property, inscribed in 2013 as "Fujisan, sacred place and source of artistic inspiration." The forest also forms a Special Protection Area within Fuji-Hakone-Izu National Park, placing it under multiple overlapping conservation regimes.
- Is it true that compasses do not work in the forest?
- Compasses still work in most areas. The basalt rock contains iron-bearing minerals that can locally deflect a needle when held close to the ground, but the popular claim that compasses fail entirely is not accurate. The genuine navigational difficulty is visual: thick canopy, repeating terrain, and no streams or distinctive landmarks.
- Are the lava caves suitable for children?
- Fugaku Wind Cave is the most family-friendly, a single horizontal tunnel with handrails and lighting. Narusawa Ice Cave includes a steep descent and a low ceiling section that small children may find difficult. Saiko Bat Cave is the longest and includes uneven sections. All three charge a modest admission and stay open from 9:00 to 17:00, weather and conditions permitting.
Basic Information
| Official name | 富士山原始林及び青木ヶ原樹海 (Fujisan Genshirin oyobi Aokigahara Jukai) |
|---|---|
| Designation | National Natural Monument |
| Original designation | February 24, 1926 (Taishō 15), as "Mt. Fuji Primeval Forest" |
| Renaming and expansion | March 8, 2010 (Heisei 22), with the addition of Aokigahara Jukai |
| Designation criterion | (ii) Representative primeval forest; rare forest plant community |
| Location | Fujikawaguchiko-cho and Narusawa-mura, Minamitsuru-gun, Yamanashi Prefecture |
| Approximate area | About 30 km² (Aokigahara portion) |
| Elevation | 920–1,300 m (Aokigahara); above 2,000 m at Oniwa-Okuniwa |
| Dominant species | Tsuga sieboldii, Chamaecyparis obtusa, Picea torano, Pinus parviflora, Pinus densiflora, Quercus crispula |
| Wider designations | Fuji-Hakone-Izu National Park Special Protection Zone; component of UNESCO World Cultural Heritage "Fujisan, Sacred Place and Source of Artistic Inspiration" (inscribed 2013) |
| Access | About 30 minutes by Fuji Kyūkō Saiko Loop Retro Bus from Kawaguchiko Station to Saiko Kōmoriana, Fūketsu, or Hyōketsu stops |
References
- Agency for Cultural Affairs: National Cultural Property Database
- https://kunishitei.bunka.go.jp/bsys/maindetails/401/1096
- Cultural Heritage Online: Fujisan Genshirin oyobi Aokigahara Jukai
- https://bunka.nii.ac.jp/heritages/detail/216389
- Shizuoka University Disaster Prevention Center: Aokigahara Lava and Lava Tree Molds at Narusawa
- https://www.cnh.shizuoka.ac.jp/research/barchive/mtfuji/026-2/
- Shizuoka University Disaster Prevention Center: The Jōgan and Hōei Eruptions
- https://www.cnh.shizuoka.ac.jp/research/barchive/mtfuji/003-2/
- Yamanashi Prefecture Official Tourism Site: Aokigahara Walking Trail
- https://www.yamanashi-kankou.jp/kokuritsukoen/jp/miryoku/hiking/course3.html
- Fugaku Wind Cave / Narusawa Ice Cave Official Site
- https://www.mtfuji-cave.com/
Last verified: 2026.05.19