Visit Iya Valley for a geology lesson on the Fossa Magna fault structures & mountain formation

The Iya Valley is an off-beaten tourist destination in its own right, but it makes a special educational experience for students interested in geology and geography. 

Iya Valley and suspension bridge (Wiki Media source)
Iya Valley and suspension bridge (Wiki Media source)

Here are some reasons to visit Iya Valley:

– Visit the Fossa Magna Museum in Iya Valley for a lesson on the Fossa Magna, a major faultline running through Japan is an important geological part of Japanese topography. The Fossa Magna lies at the junction of the North-eastern Honshu arc, the Southwestern Honshu arc and the Izu-Bonin arc. The region is famous for precarious peaks and gorges because all the mountains in Japan of more than 3,000 m in height (except for Mt. Fuji) gather in the central part of this region. It is referred to as the Central Ranges or Japan Alps and is composed of three mountain ranges (HIDA, KISOand AKAISHI) that align in the NNW-SSW direction.

The Iya Valley in the heart of the Fossa Magna and at the junction of three major faultlines, makes an excellent spot for an expedition to study earthquake formations and particularly fault structures.  The Japan Alps has several tectonic/fault lines, due to the interaction of the Eur-asian (EURA), North American (NOAM), Pacific and thePhilippine (PHS) plates. The Central Ranges have uplifted largely through the late Quaternary. The rate of uplifting is 1–3 mm per year in the Hida mountains. To the west of the Central Ranges, many faults of predominantly strike slip-type are developing, among which the Atera fault (AF), some 60 km long and trending in the NW-SE direction, is one of the most active faults. The Central Ranges are bounded by this fault to the southwest while the Itoigawa-Shizuoka Tectonic Line (ISTL), a huge fault at the western periphery of the Fossa Magna, bounds the Central Ranges to the east and geologically divides Hon-shu Island into Northeast Honshu and Southwest Honshu. The Median TectonicLine (MTL) delineates the western foot of the Akaishimountain ranges as a deep and straight fault-line valley.

Sites in Itoigawa-Shizuoka Tectonic Line fault zone make bid for UNESCO Global Geopark status
Sites in Itoigawa-Shizuoka Tectonic Line fault zone make bid for UNESCO Global Geopark status

– Another geological structure that you can study to your heart’s content are Iya Valley’s spectacularly steep river gorges. A visit to the Oboke River Gorges (see photos) and the suspension bridges overhanging them are considered a key part of any tour to the region.  The vine bridges (kazurabashi) that span the deep river gorges traditionally the only way to cross the river… are Iya’s best known tourist scenic sights.  The most popular vine bridge, Iya Kazurabashi, overhanging the Iyagawa River. It is accessible being close to the main village in West Iya. Not very far off is another suspension bridge which has been desginated an important folkloric property as one of Japan’s three rare bridges. A 30 km hike upstream in the eastern part of the valley are two more double vine bridges to visit, the Oku-Iya vine bridges: the Husband’s Bridge (Otto-no-hashi), the longer and higher up bridge, and the Wife’s Bridge (Tsuma-no-hashi).

– The valley is becoming famous for the traditional thatched homes perched high in the mountains with spectacular views overlooking the Iyagawa River, and the fresh, clean air of the Iya Valley. Of some renown with the foreign community is the Chiiori Project(Cottage of the Flute), an NPO outfit, a 300-year-old thatched heritage farmhouse conservation effort by Alex Kerr (Lost Japan) and travel writer Mason Florence. It is not just an Edo-period architectural conservation project but an effort to revive traditional lifestyles vital to Japan’s living heritage as well.

Note: The Chiiori Project is not a hotel, nor an inn, nor a B&B. But it is a working farmhouse visited by hundreds each year, some of whom stay and actively volunteer their help to restore traditional practices, actively participate in a rural lifestyle and learn about farming, roof thatching or carpentry. The majority of visitors, however, are there to experience the romance of the old Edo-thatched house, sample the rustic homemade dinner by the irori hearth.

– Iya Valley makes a good subject for a study of mountain formation. Naturally nestled among dramatically steep mountains and situated in the west of Tokushima and nearly in the centre of Shikoku Island, the Iya area forms part of Mt. Tsurugi Quasi- National Park. Hiking Mt. Tsurugi (locally as Kenzan or “Sword Mountain”) is a good reason to visit the spot … Mt Tsurugi is the most popular hiking destination. At 1955m it is the second tallest mountain in Shikoku at 1955m.


Getting There

Getting to Iya Valley is fairly easy. However, discovering the valley by public transportation is a little tricky and is best approached by car.

By Plane

It’s about 1 hour and 15 minutes to Tokushima Airport from Tokyo Haneda Airport and about 35 minutes from Osaka Itami Airport. Then add 30 minutes from Tokushima Airport to Tokushima Station by bus. From there, it’s about 1 hour and 10 minutes from Tokushima Station to Awa-Ikeda Station by JR Tokushima Line Limited Express.

By Train

The nearest train station is at Oboke, which is along the JR Dosan Line between Kochi and Takamatsu and runs hourly from Okayama (Shinkansen station). You can also reach Oboke by train, 1h20min from Takamatsu by Limited Express (¥3,410).  From Oboke you can connect to a bus through a tunnel into West Iya, but services are infrequent: there are up to eight buses per day on weekends only in the high season (April-November), and just four per day the rest of the time (4 buses a day to Kazura-bashi Bridge (25min).

By Bus

There are seven direct buses daily from Ikeda, which travel to West Iya either via Oboke (four daily) or via Iyaguchi (three daily).

Bus tours: To tour both the Oboke Gorges, the Kazura-bridge and the Iya Valley between the Bridge and Awa-Ikeda Station, try Shikoku Kotsu tours (定期観光) of the whole region every day from March to November. Buses from Awa-Ikeda Station leave 7 times a day (between 7:15am and 4:15pm) to Kazura-bashi Bridge, either via Iya Onsen, or Oboke, and take 2h10min. (¥5,200 including various admission fees, lunch and transportation). Tours start from 11am from Awa-Ikeda Station, where they return at 4:20pm.

By Car

Travelling by car is by far the best way to discover Iya Valley and the fastest route if arriving from Tokushima and Kansai. Take Route 438 from Sadamitsu or Route 439 from Anabuki which connect directly into East Iya. Traffic is very light, especially on weekdays, and the roads are quite narrow and twisty.

The Chiiori Project

Higashi Iya Tsurui 209, Miyoshi, Tokushima-ken 778-0206
Tel: 0883-88-5360 / 0883-88-5290

Camping sites: see Iya Valley Campsite (in English) /  Iya Valley Campsite (in Japanese)  

Sources and further readings:

A Journey to the Tibet of Japan“, Kansai Scene Mag feature

Iya-kei Valley and Oboke Gorges, Japan Reference

Variable density determina-tion across sub-surface fault-like structures by I.L. Ateya and S. Takemoto

Iya Valley


COPYRIGHT.  Education in Japan

2 thoughts on “Visit Iya Valley for a geology lesson on the Fossa Magna fault structures & mountain formation”

  1. hi there,

    I find your blog helpful .lot of links .

    I am an architect .I am interested to live with a community and work with them .I am willing to teach them english or plan out their everyday community needs .May be designing them houses or civic amenities .

    I came across The nature school in Tsurui, Akan-gun,

    Hokkaido 085-12…but it seems they don’t have any website.
    I am open to similar initiations .If you come across any , kindly let me know.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s