10th Asian Regional Conference of IAEG (2015)

Invitation to the Geo-Tetsu Tour by Train Trips, Visiting of the Railway Route for
Geohazard: A Case Study of the JR Dosan Line in Shikoku, Southwest Japan
Hironori KATO (1), Masayo FUJITA(1) , Shunji YOKOYAMA(1),
Shoji UENO(1), Tadashi YASUDA(1), Keisuke IMAO(1), and Yasumasa SUGA(1)(1) Geo-Tetsu Project Committee of the FGI, Fukada Geological Institute, Japan
E-mail: hironori.katou@aratani.co.jp
Abstract
Since 2009, Geo-Tetsu by train trips has been known as a tool of dissemination ofearth sciences to the general public (Kato et al., 2009a). Japan is covered by a dense
network of railway lines, even over its mountainous parts. There are steep slopes, sharp
curves, landslides and various geohazards caused by fragile foundations along the railways.
Many technological inventions were introduced to overcome these difficulties: the river
improvement works, switchback operations, and re-routing lines. This research deals with
the Geo-Tetsu route of the Dosan line operated JR Shikoku which coexists with geohazards
for an important case study of such phenomena. We visit the various kinds of Geo-Points
with geohazards, even along the disused line (old tracks, tunnels, bridges, rock sheds,
rockfall protection, etc.). There we can touch the advancing technologies to maintain thesafety operation of the railway, and feel the endeavors of engineers with loyal working
facilities.
Keywords: Geo-Tetsu, Geo-Point, Dosan Line, disaster, disused line, railway facility
1.

Introduction

role. On the train, the Geo-Points will give you somechange, listening to motor sound, feeling the grades
and the curves, and viewing railway facilities fordisaster prevention through the window. You can also
get off the train and walk around the disaster areas
and along the disused line. There, you can think about
the characteristic geohazard of local area througheach geological background and the efforts ofengineers. In this paper, we will trace the Geo-Tetsu
route focused on geohazards understanding thegeological setting and geographical features along the
Dosan Line. Specifically, the Dosan Line wasconstructed disaster area in Japan, and many
characteristic railway facilities exist there. Tracing
them, we will show that the history of the Dosan line
overcoming the disasters.

Railway is the commonest transportation system
in Japan. Its dense network covers even overmountainous parts which account for 70% of ourcountry. The constructions of railways are directly
related to geological setting and geographical features.
That affects not only the route selection but also thefacility specifications and safety operation.
Geo-Tetsu by train trips has been known as a toolof dissemination of earth sciences to the generalpublic since 2009 (Kato et al., 2009a, 2009b; FujitaM., 2012; Fujita et al., 2013). The name Geo-Tetsu islicensed as the trademark No.5378786 by Fukada
Geological Institute (Fujita M., 2012; Fujita et al.,2013; Geo-Tetsu website http://fgi.or.jp/geo-tetsu/).
We will recommend many attractive Geo-Points
where people can see representative geoscientificphenomena and railway heritages. It can offer theopportunities to get contact with geoscience intravelling by trains. Here we introduce the railway
route which coexists with geohazards.
.
2.

3.

Region of the Dosan line

The Dosan Line is the main railway of Shikoku
Island and connects to Okayama via the Great Seto
Bridge. It is 198.7 km in total distance, crossing theisland from Tadotsu facing the Seto-Inland Sea to
Kubokawa on the Pacific coast. Shikoku Island iscovered by the high mountains uplifted by tectonic
motion of plates and the deep valleys are formed byerosion. Therefore the flat ground is limited, theGeo-Tetsu tour focused on geohazards

When you take a Geo-Tetsu route, Geo-Points
with comprehensible commentary play an important1

10th Asian Regional Conference of IAEG (2015)

4. The Dosan Line overcoming the disasters
4.1 Cross the mountain pass by switchback
The Sanuki Mountain district which consisted of
Cretaceous Izumi Group is located at the border ofKagawa and Tokushima Prefecture. The Sanuki
Mountain district is rifting by active faults of Median
Tectonic Line (MTL), and the deep valleys is forming
by erosion of branches of Yoshino River at the southfoot of the mountain. There are also landslide zones
affected by active faults of the MTL, surprisingly,
some villages are scattered at the upper part of steep
slope in the landslide (Photo.2). This section between
Sanuki-saida Station and Hashikura Station is one ofthe difficult constructions in the Dosan line.
When the train goes over the Sanuki Mountains, it
must run up continuous grade 25 ‰. In order to makethe train stop and depart safely in the middle of theincline for going over the mountain pass, theswitchback was constructed at Tubojiri Station
opened in 1929 as signal station. The station andswitchback facilities were constructed on the artificial
land which filled up a river channel (Fig.2，Photo.2),
because that was located in the rugged valley, andlittle flat ground was around there. The flow of theriver was changed at three places, and they weretransferred by headrace tunnels. At a glance, thelocation of the station looks dangerous, but theerosion does not advance in old river channel, and thefilling abutted the valley wall is stable enough tocollapse. Therefore the area is relatively safe fromdisaster.
Even now, the switchback operating does when

Photo. 1 JR Dosan Line crossing the Shikoku
Mountains, Southwest Japanrailway lines constructed on the riverside steep slope(Photo.1). The train runs through the wholegeological structure of the Shikoku area from North
to South (Fig.1). The characteristic of geohazards aredifference of each geological setting. Various
methods were taken for safety operation of therailway by engineers when the Dosan line was
opened.

Fig.1 Geological map of Shikoku Island and the route of the JR Dosan line
(Geological map based on Editorial Committee of Shikoku, Regional Geology of Japan, ed., 1991)

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10th Asian Regional Conference of IAEG (2015)

Fig.2 Map around the Tsubojiri station of the Dosan Line
(Kato, 2013; Base map Kashmir 3D, http//www.3d.com/)

4.2 Replacement railway line due to disaster
Replacement the railway line of the Dosan line has
been promoted for disaster prevention (refer to Fig.1
and Table1). We can find the disaster topography andthe disused line from the train window, when the train
goes in continuous short curves, makes the groan ofengine sound and increases the speed throughreplacement section in a long tunnel.
In October, 1945, a landslide occurred by the heavy
rain of typhoon in Kunimasa area between
Awakawaguchi Station and Nishiu (now Koboke)
Station, and the extension 270m of railway line wasburied. It took two months for recovery after thedisaster. In order to avoid the secondary damage oflandslides, the 2,178m Yamashirodani tunnel wasconstructed in 1950. It was said that the large quantityof spring water welled out during the Yamashirodani
tunnel digging was effective for making the landslide
stable unexpectedly. This is the oldest replacement
section of the Dosan line.
In September, 1948, the slope collapse occurred
two times along the Dosan line between Iwahara
Station and Toyonaga Station, and the locomotive
derailed. For protecting from the accident, it wasconstructed a rock shed extended 33m there, however
in February, 1962, the shed fell down together withthe railway track to Yoshino River. It is consideredthat the accident was caused by distributions of thecrystalline schist in this region. It was exfoliated andcollapsed after creep deformation for a long time
(Yamada et al. 1971). In this case, the train which wassuspended slope was checked by the survey prior to

Photo.2 Overlooking view of the Tsubojiri stationand the landslide on the mountain (Kato, 2013)
the local train runs through the Tubojiri Station. The
passengers are surprised that the train and trackchange the direction and the reverse scenery. Whenyou get off at the Tubojiri Station, you can feel theendeavors of the engineers with loyal working
railway facilities.

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10th Asian Regional Conference of IAEG (2015)

Table.1
periodsectionNov.1950

AwaKawaguchi～ KobokeAug.1956

Oboke～

Nov.1968

Oboke～

Aug.1963

Re-routing sections of the Dosan Line

newly founded structures

remains of structure

relating natural disasterYamashirodani TN (2178m)

many piers and ditchs

landslide by typhoon, Oct. 5, 1945

TosaIwahara

Shushi TN (860m)

tunnellandslide with subsidence and moving of roadbed
and deformation of retaining wall

TosaIwahara

Oboke TN (4179m)

tunnel, piers

landslide with deformation of retaining wall,rock-fall damages

TosaIwahara～ Toyonaga

Oshiro TN (675m)

topography of collapse

landslide with derailment, Sep.,1948, and landslidewith a shed and railway track, Feb.,1962

Jun.1954

Otaguchi～TosaAnanai

Wada TN (1198m)，
Trasfer of the Tosa-Ananai Sta.

Nishiyashiki TN，Akimori TN,
Ananai Bridge

consecutive deformation around Nishiyashiki TN
by slow moving landslide

Feb.1973

Osugi～

TosaKitagawa

Osugi TN (2583m)

Yoboushi Bridge (pathable)landslide, May 1966

Mar.1986

Osugi～

TosaKitagawa

Otoyo TN (2067m)，Transfer of the
Tosa-Kitagawa Sta. on the bridge

many tunnels and bridges

rock-fall damages etc.

Note： Data based on Tamura T., ed., (1968), Yamada, G., et al., (1971), Kubomura K.,(1973), Imao K. (2007), Yokoyama, S., et al., (2012) , and Kato, H., (2014)

Fig.3 Walking path looking at abandoned tracks between Osugi Station and Tosa-Kitagawa Station(Yokoyama, S., et al., 2012; Kato, 2014; Base map Kashmir 3D http://www.kashmir.3d.com/)the collapse. In the next year, this section changed theroute to the 675m Oshiro tunnel. There we can see thehuge landslide above disused line and watch a lot of
falling rocks in the Yoshino River, from the Route 32
paralleled to the Dosan line.

between Osugi Station and Tosa-kitagawa Station(6.1km) along the Ananai River at the Kochi
Prefecture (Fig.3; Photo.3-a; Yokoyama, S., et al.,2012). The train must run over the toe of landslidethat consists of Mikabu greenstones in northern partof the section. On the other hand, it must run throughthe rock-fall area that consists of quartz schist in
southern part of the section. There are many disasters
occurred frequently, the railway route on river side
was changed to two long tunnels and a railway
bridge.
In northern part, the 2,583m Osugi tunnel was dug
to avoid the landslide as alternative route in the

4.3 Disused railway lines by disasters
Even today, we can recognize railway tunnels,
railway bridges, communications cable facilities,
rock-fall protection fences, and detectors for fallingrock etc., along the disused railway lines as many
railway inheritances due to disasters.
The longest disused section in the Dosan line exists

410th Asian Regional Conference of IAEG (2015)ab

Photo.3

a：Remains of railway bridge located between Osugi Station and Tosa-Kitagawa Stationb：Tosa-Kitagawa Station built on a railway bridge

underground. We can read from a topographical map
the aim of replacement of the railway (Fig.3). The
new route is shorter and more straight line than
ex-route, the train is able to pass at high speed
consequently.
In southern part, Tosa-Kitagawa Station wastransferred to a railway bridge from the ex-location
along the Ananai River. The station having a platform
on a railway bridge is rare in Japan (Photo.3-b). The
construction of Tosa-Kitagawa Station on the railway
bridge is advantageous for disaster prevention,
because it does not suffer from influence of the slope
failure directly. We can recognize that a lot of hugequartz schist rocks of the past collapse still remain in
the Ananai River.

approximately three months, because the roadbeds
flowed by the flood disaster occurred in Kochi
Prefecture. More recently, in August 2014, therailway route at border of Tokushima and Kochi
Prefecture was suspended for 12 days, because of theroadbeds collapsed by typhoon. In those two cases,
although the passengers were inconvenient, the trains
and human life did not damage.
In contrast to them, the large-scale slope failure
took a heavy toll of human lives at Shigeto Station in
Kochi Prefecture on July 5, 1972 (Photo.4). The
heavy rain continued for two days, it triggered thecollapse. At first, the slope collapsed within the small
area several times, at the north side of Shigeto Station
facing to Route 33. And then, a large slope failure
occurred around 10:50. The train which just stopped
at the station was involved in the debris flow and fellto the Ananai River. About 60 people that were thecrews, the passengers, the inhabitants, and the firefighters etc. died of the disaster. In the source area
there is distributed the Chichibu terrane which wasformed in high angled reverse-dip. It is suggested that

4.4 Recent railway disasterFor geohazards, it has been performed various
measures along the railway route of the Dosan line,
but in recent years railway disasters often occur.
In 1998, the Dosan line between Shigeto Stationand Shingai Station was forced to the suspension of

Photo.4：Shigeto Station six days after the disaster on July 11, 1972. The station facilities
and the stopped train were washed away by slope collapse (Photograph by OYO Corporation）

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10th Asian Regional Conference of IAEG (2015)

the collapse was happened by unstable and long-term
weathering. It is one of the examples that showed thestrictness of nature in Shikoku mountain district as aslope disaster. Now surroundings of the Shigeto
Station are restored, there we can understand thedisaster to compare with the present and the past by aphotograph.

Wonders of the Geological feature and theTopography of Shikoku District by Train. no.20, thenewspaper the Kochi Shimbun, 15 Nov., p.10 (inJapanese).
Kato, H.,(2013): Geo-Tetsu Trip - Let us Enjoy
Wonders of the Geological feature and theTopography of Shikoku District by Train. no.6, thenewspaper the Kochi Shimbun, 21 Sep., p.12 (inJapanese).
Kato, H., Fujita, M. and Yokoyama, S. (2009b): Letus enjoy Geo-Tetsu - a proposal of Geo-tours
through Train Windows: First proposal of its course,
JR Dosan Line in Shikoku, Chikyu Monthly,vol.31,
No.8, pp.445-454 (in Japanese).
Kato, H., Fujita, M. and Yokoyama, S. (2009a): Letus enjoy Geo-Tetsu - a proposal of Geo-tours
through Train Windows: First proposal of its course,
JR Dosan Line in Shikoku, Japan Geoscience Union
Meeting 2009, A004-P012.
Kubomura K.,(1973): Analysis of an Example ofSlope Failure in JNR and Studies on Foreboding ofDanger Ratio. Railway Technical Research Report,
no.878,pp.1-229 (in Japanese).
Tamura T., ed., (1968): The History of Sanmyou
village (Sanmyo Sonshi), Yamashiro town office,
Tokushima, 670p (in Japanese).
Yamada, G., Watari, M. and Kobashi, S. (1971): The
actual situations and countermeasures against
Landslides (Jisuberi shamenhoukai no jittai totaisaku).Sankaidou, Tokyo, 580p (in Japanese).
Yokoyama, S., Fujita, M., and Kato, H. (2012): in
The Story of the Moving Earth in Kochi, Japan(Saishin Kochi no Chishitsu, Daichi ga Ugoku
Monogatari), ed. Suzuki, T. and Yoshikura, S.
(Minaminokaze Press, Kochi), pp.124-146 (inJapanese).

5. Conclusions
The slope disasters along the Dosan line arecaused by the fragile geology and the steep
topography. It is the characteristic of the Dosan linethat we can understand the earth movement and themechanism of the disasters as a familiar railway
history. In other words, the history of the railway
disasters is the most familiar evidence as the
movement of the earth. In harsh natural environment,
the engineers continue keeping maintenance of thesafety service of the railway, and the railway facilities
remain as results of their effort. We hope the
Geo-Tetsu tour becomes to know the diversity of theearth, and it becomes an opportunity to get a chancein the method of preventing disasters. The pleasure of
the Geo-Tetsu is acquires knowledge along therailway by oneself. Everything we feel through thetrain trips as Geo-Tetsu bears somethinggeoscientific.
Acknowledgements
The authors are grateful for the significant
contribution from the support members for activitiesof our Geo-Tetsu Project Committee of the FGI.
References
Editorial Committee of Shikoku, Regional Geologyof Japan, ed., (1991): Regional Geology of Japan,
Part 8: Shikoku. Kyoritsu Shuppan, 280p.
Fujita, M., Kato, H., Yokoyama, S., Ueno S., YasudaT., (2013): Geo-Tetsu Project: the History of
Dissemination Activities of Geoscience for FourYears (2009-2012), Japan Geoscience Union
Meeting 2013, MIS32-P9.
Fujita, M. (2012): Geo-Tetsu project: dissemination
activities of geoscience for four years (2009-2012),
Annual Report of Fukada Geological Institute,
No.13, pp.13-20 (in Japanese with English abstract).
Geo-Tetsu Project Committee of the FGI. “Geo-Tetsu
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Imao K. (2007): in Railway Travel in JapaneseIslands (Nippon Rettou Tetsudou Kikoh), ed. Ohno
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Kato, H., (2014): Geo-Tetsu Trip - Let us Enjoy

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