10th Asian Regional Conference of IAEG (2015)

Historical and pre-historical gigantic landslides in Tateyama Caldera and their mechanism ofoccurrence
Tamotsu NOZAKINOZAKI EG Consulting, Japan E-mail:nozakit@kb3.so-net.ne.jp
Abstract
This paper examines the mechanism and the genesis of a cluster of deep-seated and very large
landslides in the Tateyama Caldera. There is a big depression, called the “Tateyama Caldera” in the Northern
Japan Alps. This caldera, however, was not formed by volcanic activities but created by mass wastingprocesses which are still active as the site is littered with steep unstable slopes of historic and pre-historic,
deep-seated and very large landslides. The basement rocks in the region consist mostly of granodiorite whichis extensively sheared and locally hydrothermally altered as the caldera is located along one of the major
active fault systems in central Japan. The higher elevations and rims of the caldera are underlain by middle tolate Quaternary volcanic deposits. Active erosion of the unstable slopes and the possibility of deep-seatedlandslides pose serious future problems. To further complicate the situation, the bottom of the caldera isunderlain by thick deposits of older landslides and related debris. Furthermore, recent studies revealed thatthe interior of the caldera is covered with older gigantic landslide deposits and/or extremely unstable slopes.
This study examines past geologic events related to the causes of deep-seated landslides and the genesis of
the caldera, then discusses the mechanism of deep-seated and very large landslides, and finally, warning
against possible future failures of the unstable slopes surrounding the caldera, and suggests risk reduction.
This research is based on detailed reports by Nozaki and Kikukawa (2012,2014).
Keywords: Tateyama Caldera, deep-seated landslide, earthquake, alteration

1.

Introduction
It had been believed that any types of deep-seatedlandslide were hardly triggered by earthquake among most of
the specialists until the end of the last century. In Taiwan,
however, many big or gigantic landslides such as the Tsaolingand the Chiu-fen-erh-shan landslides were triggered by the1999 Chi-Chi earthquake (Chigira et al., 2003; Wang et al.
2003). This disastrous event was followed by some big
earthquakes triggering large number of hazardous
slope-movements including deep-seated landslides such as
the cases of the 2004 Mid-Niigata Earthquake and the 2008
Iwate-Miyagi Nairiku Earthquake in Japan, and the 2008
Wenchuan Earthquake in China (JLS, 2007, 2012; JSEG,
2009). World-wide climate change, to make matters worse,
has caused many serious natural disasters including
deep-seated landslides due to the heavy rainfall in recent years,
not only in Asian countries but also in many parts of theworld.
In this context, the author has been making researcheson the mechanism of deep-seated landslides which weredeeply related to the occurrence of the Tateyama Caldera,
T
o
y
a
m
a
Fig.1 Location of the study area and distribution of active
faults in Toyama-prefecture.

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10th Asian Regional Conference of IAEG (2015)

prefecture (Fig.1). There is a big oval depression at thesouthwestern side of Mts Tateyama in which the highest peakisFig.2 Topography of Tateyama Caldera and distribution of Tombi-doro, Kunimi-doro and Kunimi landslide (Nozaki & Kikukawa,2012). Enclosed red lines indicate expected unstable slopes for future earthquakes.
with two events of landslide-dam failure, run down the mainvalley of the Jyoganjigawa within a few months. The
debris-flow deposits so-called “Tombi-doro” extensively
covered the Toyama plain and their toes reached to the Japan
Sea. Many residents or farmers were killed by those debris
flows, and the farm land was severely devastated for a longtime. This event has been recorded as one of the three biggest
historical slope-failures in Japan, and notwithstanding the
longtime countermeasures against the erosion in the caldera,
which have been executing by the central government for 90
years, the future threat of deep-seated slope-failures have notbeen removed yet at all.

3015m a.s.l. This depression so-called Tateyama Caldera,
however, is not volcanic origin but erosion principally due tothe active mass wasting including deep-seated landslides. The
consequence of the researches is that those big or gigantic
primary landslides were triggered by repeated activities of the
Atotsugawa fault system and made an important role for theoccurrence of the caldera.
In the early spring of 1858, the Hietsu Earthquake(Mj=7.3) hit the region of Toyama-prefecture and thenorthern part of Gifu-prefecture, by which a gigantic
deep-seated slope failure so-called “Ootombi-kuzure” wastriggered. Total volume of this slope failure had been
estimated at 4.1×108m3 by Machida (1962). The estimation
by recent researches, however, is a little more than 2.0×108m3(Nozaki and Kikukawa, 2014). It depends on both of
1.0×108m3 by Fujii et al. (2011) at the area of Toyama plain(Jyoganjigawa alluvial fan) and 1.27×108m3 by Ouchi and
Mizuyama (1989) at the source area including upper reachesof the Jyoganjigawa. More than half of the landslide debris
run out from the limits of the caldera, and built up twolandslide-dams at the confluence of the Yukawa and the
Makawa (Fig.2). After that, the debris-flows which occurred

2.

Topographical and geological settings
Fig.2 shows the topography of the Tateyama Caldera
and the distribution of late Quaternary clastics. The scale ofthis caldera depression is about 6.5km long to the ENE-WSW
direction, 4.5km wide to the NNW-SSE direction and morethan 500m deep surrounding by high escarpments. The mainstream Yukawa in the caldera, which has its rise on thewatershed of two river systems the Jyoganjigawa and the
Kurobegawa, flows westward meeting with branch gorges2

10th Asian Regional Conference of IAEG (2015)

slope “Outa-men” adjacent to the eastside of the circulardepression was formed by the pre-historical rockslide“Kumini landslide” (Nozaki & Kikukawa, 2012).
Basement rocks of the caldera mainly consist of
Mesozoic granodiorite. They are extensively affected by thepast hydrothermal alteration especially along the active fault“Yukawadani fault”, and thickly covered with Tombi-doro,from its both sides on the way to the confluence of Makawa.
Although hundreds of scars due to the active slope failures areconspicuous in the caldera at present, two inner depressions
should be given more attention from a view point of theoccurrence of this big depression. One of them occupies its
southwestern part showing the external form of parallelogram
which is called “Dashihara” orFig.3 Aerial photograph of Dashihara depression overlooking
from the north (Photograph by Takashi Inokuchi)

Fig.5 Topographical map of north side slope of Yukawa-dani(1/25000 map by GSI)

Fig.4 Whole view of Tateyama Caldera. Circular depressionof foreground is the source area of Kunimi-doro. Dashihara
depression can be seen on the right. (Photograph by Takashi
Inokuchi)Fig.6 Classification for activity stages of Tateyama volcano
and their distribution (Harayama et al., 2000)
Kunimi-doro and other landslide debris or debris-flow
deposits at the lower portion of the caldera. On the other hand,
thick Yukawadani-volcanic-rocks of the stage 1a occupy thecentral part of the caldera of which the lower formation looks
like a sort of “green tuff”, and rocks of older 3 stages (1a-3) of
the Tateyama volcano are generally distributed at the higher
portion as shown in Fig.6. In particular, beyond the northern
limits of the caldera the extensive gentle slope so-called“Midagahara” highland is composed of thick lava andpyroclastic flow deposits. Although the volcanic activity isdormant in the stage 4 at present, sulfurous fumarole(solfatara) activity is active at the northern part of the popular
sightseeing spot “Murodo” where is close to the northeastern“Dashihara depression” (Fig.3), and another one is located at
the western side of Mt.Kunimidake showing a shape of big
bowl (Fig.4 & Fig.5). The 1858 Ootombi-kuzure occurred at
the southeastern part of the former one burying the old
Dashihara with its thick debris of Tombi-doro, and made thefloor of gentle relief. Buried under the Tombi-doro, the rockmass of “Dashihara landslide” has been found by drilling test.
The latter depression used to have been believed as a remnant
of volcanic crater because of the circular depression. It is now
clarified, however, that the wide high-terrace so-called“Matsuo-daira” along both side of the Matsuo-dani, which isadjacent to the lower end of the circular depression, is
composed of very thick debris of “Kunimi-doro” derived
from this depression. Besides, it is clarified that another gentle3

10th Asian Regional Conference of IAEG (2015)

are originally distributed at much higher place (see Fig.14).
Although the age of this landslide is unknown, it must notexceed 30ka as the same reason as the age of the
Kunimi-doro described below. The author named it“Dashihara landslide”, it might not have occurred with asingle event though.
Harayama et al. (2000) had indicated the distribution ofold debris deposits, which were extensively distributed
around the confluence of Yukawa-dani and Matsuo-dani, andtheir origin with no detail mechanism. After that, the author

limits of the caldera. Small fumarole activities or hot-springs
can be seen even in the caldera (see Fig.10).
3. Geological events in the past
3.1 Deep-seated landslides
Fig.7 shows the distribution of Tombi-doro,
Kunimi-doro, Kunimi landslide and the section line for the
Dashihara landslide. With the occurrence of the 1858
Hietsu Earthquake, snow-capped two peaks of Mt.Ootombi
and Mt.Kotombi, which had

Fig.7 Distribution of Tombidoro, Kunimidoro, Kunimi
landslide
been situated at the southeastern end of the Dashihara
depression, run down as a gigantic rock avalanche(Ootombi-kuzure), by which about 30 people were killed at
the old “Tateyama hot-spa” located at the northern end of
Dashihara depression. The debris of rock avalanche dammed
up making two lakes at the confluence of the Yukawa and the
Makawa. Within a few months, these dams were successively
broken down with overflowing water, and the debris flowed
down the gorge of the Jyoganjigawa. As a result, enormousvolume of debris-flow deposits extensively covered the farmland causing thousands of casualties including more than 140
loss of lives, which was called Tombi-doro by farmers after
the disaster. About 100 years later in 1964, big slope failure of
2.68×106m3 took place at the head scarp ofOotombi-kuzure, but it was much smaller than the past one(see Fig.13).
Ouchi and Mizuyama (1989) had indicated theexistence of landslide debris underlying the Tombi-doro. After
that, 95m deep drilling test were carried out near the old
Tateyama hot-spa in 2008. Fig.8 shows the geological column.
The author examined the core by courtesy of MLIT Tateyamasabo office, and confirmed thick Yukawadani-volcanic-rocks.
They are, however, evidently a part of old rockslide-mass
overlain by Tombi-doro, because the drilling site was close to
the granodiorite outcrop making high waterfall in the
Kanayama-dani, and the intact Yukawadani-volcanic-rocks

investigated its distribution, facies, chronology, and etc. As aresult, it is concluded that this thick debris deposits
Kunimi-doro, which is more than 100m deep including
h o u s e - s i z eb o u l d e r s ,Fig.8 Geological column judged from the drilling test near the
Tateyama hot-spa (Nozaki & Kikukawa, 2012)
was derived from the circular depression of the upper slope asa hazardous rock-avalanche. On the other hand, it is clear thatthe source area of the Kunimi-doro was the right wing of the
Kunimi landslide of which the depth to the sliding surface
might reach to 300m (see Fig.15).The age of these gigantic
failure and rock slide is estimated around 30ka from therelation between the Kunimi-doro and the terrace deposits at
the lower reaches of the Jyoganjigawa which are now
covered with tephra AT of 26-29ka (Fujii &d Kaneko, 1999;
Nozaki & Kikukawa, 2014). Besides, it is reported that thelatest lava so-called “Tamadono-yogan” (30-60ka) erupted
within the limits of eastern end of caldera and flowed
northward down to the Murodo over the northeastern limits ofthe caldera (Shimizu et al., 1988; Harayama et al., 2000), and410th Asian Regional Conference of IAEG (2015)

the old Makawa lake existed until 60ka at most (Kikukawa etal.,2005).

Fig.9 Outcrop of Yukawadani fault (Nozaki & Kikukawa,2014)

3.2 Active fault traversing the caldera
The 1858 Hietsu Earthquake was generated by the
Atotsugawa fault, of which the outcrop has been found during
the construction work in the Makawa gorge (see Fig.10) anddesignated as a natural monument by the government.
Although the eastward extension of this fault is traceable to
the western caldera-wall as one or two photo-lineaments, nofarther evidence had been found in the caldera. The author,
however, recently found the outcrop of active fault at the leftbank of Yukawa-dani as shown in Fig.9, where is close to theconfluence of Matsuo-dani. Although the ENE strike of thisfault is parallel to the Atotsugawa fault, it does not likely array
together on a single line. It might be conjugated with NNW
faults as shown in Fig.10. It

Fig.10 Distribution of active faults and three stages ofalteration
has not, however, necessarily been able to identify as a part ofthe main fault. Hence Nozaki and Kikukawa (2014) named it“Yukawadani fault” as a local name.
3.3 Three stages of alteration
Nozaki and Kikukawa (2014) reported that threedifferent types of alteration were recognized and partiallyoverlapped each other in the caldera as shown in Fig.10.
Fig.11 shows the outcrop of intensively deteriorated zone
located at the right bank of the Dashihara-dani, which isfine-fragmented with thick kaolinite-rich clay veins due to thestageⅠhydrothermal alteration. This zone is gently tilted
toward the center of the Dashihara depression. The alteration
is extensively propagated and not well defined the limits, butvery wide zone along the Yukawadani fault arecharacteristically deteriorated. The epoch of this alteration is
unknown but much older than overlying volcanic rocks,
because the affection is limited to the basement rocks.
The rock facies of stageⅡalteration looks like the
Neogene “green tuff”. It is reported, however, that the lower
half
Fig.11 Outcrop of basement rock intensively fine-fragmented
accompanying with white veins of kaolinite-rich clay (Nozaki& Kikukawa, 2012). Overlying gravel bed is Tombi-doro.

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10th Asian Regional Conference of IAEG (2015)

was facilitated by sulfuric acid produced by oxidation of
pyrite (Sato et al., 2013). Hence, many scars of slope failures
can be seen on those fragile rock slopes.
4. Mechanism of past deep-seated landslides
4.1 Ootombi-kuzure
Fig.13 shows schematic section from the top of thepre-existed Mt.Ootombi through the center of Dashihara
depression. The upper layer of Tombi-doro predominantly
consists of andesite gravels including big boulders whichwere evidently derived from the upper portion of the caldera
wall and/or the peripheral ridges, where the salfatara alteration(stage Ⅲ) was dominant. The lower layer of Tombidoro,
however, predominantly consists of granodiorite gravels
including clayey parts at places. The author, therefore,
believes that the sliding surface of this slope failure wassubstantially in the basement rock, and the primary cause ofO o t o m b i - k u z u r ew a shydrothermal alteration (stageⅠ) in the basement rock withtheFig.12 Outcrop of the boundary between granodiorite (left)
and green-altered Yukawadani volcanic rocks (right)of the Yukawadani volcanic rocks have been suffered by thehydrothermal alteration due to their own residual liquid in acircumstance of the ancient pond (Harayama et al., 2000).
These green rocks are not so fragile, but the author found acontinuous layer of viscous clay (chlorite and mixed layer ofillite-smectite) between their base and the granodiorite in the
Kanayama-dani as shown in Fig.12. Fig.14 shows thegeological section from the Kanayama-dani to the Yukawa

through the drilling site.
The stage Ⅲ alteration is due to the sulfurous
fumarole (solfatara) activity, which is related to the stage 4 ofvolcanic activities. At the higher portion of the south side
Yukawa-dani and alongside the lower banks of the Yukawa,
the color of outcrops is yellowish or reddish brown with no orless vegetation, where the solfatara activity and the following
oxidation must have occurred in unsaturated environment.
The rocks are generally fragile associating with smectite-richclay. This suggests that dissolution of rock-forming minerals

Fig.13 Schematic section of Ootombi-kuzure

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10th Asian Regional Conference of IAEG (2015)

the middle and lower layers consist of altered green rocks.
The lower layer is cracky or partially fragmented and stainedwith reddish brown due to the oxidation in spite of the
reduction zone filled with hydrothermal water, of which thetemperature reaches to 150℃ at present, and underlain by
non-oxidized soil. Of course the triggering cause cannot beclarified now, and even the primary cause has not beennecessarily known yet. It is inferred, however, that thisrock-slide mass slowly moved down the east wall ofDashihara depression taking advantage of the clay layerintercalated at the boundary between altered volcanic rocks
and granodiorite as a potential sliding surface, because theslid-mass is not so fragmented except a part of the lower layerin spite of the relative height between the present position of
intact volcanic rocks and landslide mass under the
Tombi-doro.

aid of some potential sliding surfaces such as low angle
discontinuities and/or clayey zones described above. The
shallow solfatara alteration and the following oxidation must
not have been main agents but only supplementary ones, andthey have been the cause of 1964 slope failure or otheridentical ones on the higher portion of caldera walls.

4.2 Dashihara landslide
The actualities of Dashihara landslide are not wellknown, because the landslide mass and debris are completely
covered with the Tombi-doro except for only a little at theconfluence of Makawa and Dashihara-dani. Fig.8 and Fig.14
respectively show the geological column of drilling test andsection in the proximity of the old Tateyama hot-spa. The
formation of rock facies of the core from 18.4m - 90.8m
shows those of the Yukawadani volcanic rocks, that is, theupper layer consists of weakly altered volcanic rocks, whereas
Fig.14 Geological section of Dashihara landslide depending on drilling test near the old Tateyama spa (Nozaki & Kikukawa, 2012)
Fig.15 Schematic geological section of Kunimi-landslide
4.3 Kunimi landslide and Kunimi-doro
The estimated volume of Kunimi-doro is more than 2.0
×108m3 at least, and the case of primary Kunimi landslide is
5. Forecast for future progress
In this paper, the mechanism of the historical androughly 7-8×108m3 including Kunimi-doro. The age of thesepre-historical deep-seated landslides were discussed, which
events is not well-known, but it must not exceed 30ka so
have made a big role of building-up the present Tateyama
much as described above. Fig.15 shows the schematic
caldera. On the basis of this study, the forecast for deep-seatedgeological section of the Kunimi landslide.
landslides or the future progress of caldera is discussed here.
Yukawadani-volcanic-rocks are gently tilted toward
Locations of unstable slope in the future are shown in Fig.2.
Yukawa-dani (Harayama et al. 2000), and there is highDeep-seated slope failures like those scale of Tombi-doro andpossibility of clay layer more or less between granodiorite andKunimi-doro are too big to stop or completely avoid thevolcanic rocks, because of the same geological condition as
disaster by our techniques in the near future. Hence, thethe case of the Dashihara landslide. Hence, it is reasonably
author positively tried to predict the future events or theinferred that the boundary tilted toward the valley must haveprogress of the caldera for the purpose of the disaster-riskmade a role of potential sliding surface, and this gigantic
reduction, in particular, on the following three unstable slopes.
incipient landslide was triggered by the earthquake in the
The highest provability is the lower slope ofsame manner as the Ootombi-kuzure, because it is too big to
Kunimi-landslide in which the independent peak is located at
be triggered by any other agents in this deep depression. The
the head of the secondary slide, and the upper ridge leading torock avalanche of Kunimi-doro might have occurred almost
Outa-men also looks unstable against future earthquakes (seesimultaneously with its mother-slide, it might not have been a
Fig.5 & Fig.15), because of the tilted base of thesingle event though. After that, some other minor failures
Yukawadani-volcanic-rocks toward the gorge and the convex
must have been triggered by not only earthquakes but also
shape of the topography as indicated by many recent
heavy rainfalls and snow-melting as secondary ones ofcase-studies (JLS, 2012).
Kunimi landslide.
The second one is the independent E-W ridge divided
by the col between its peak and Matsuo-pass. The geologicalcondition has not been clarified yet, but most of this ridge
consists of lava and pyroclastic flow units of stage 1b-3 (seeFig.6). Those are underlain by more or less altered
granodiorite. Hence, it is inferred that this ridge must be
unstable against future seismogenic activity (Mw>5.0). If the
deep-seated slope failure takes place in the same way as

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10th Asian Regional Conference of IAEG (2015)

Three potential deep-seated slope-failures and more arewarned against the future earthquakes in and around the
Tateyama Caldera, that is, the lower slope or the whole area ofKunimi landslide, the independent ridge on the northwesterncaldera wall, the periphery of the west marginal ridge of thecaldera and any other unstable slopes should be examined thestability for the future.

Ootombi-kuzure at this place, it will be much more dangerous
for the residents at the lower reaches than the other cases,
because the enormous volume of debris will directly hit themain valley building up a landslide-dam, and flow down withflood water as a result.
The third one is anywhere on the periphery of western
marginal ridge of the caldera. Although the extent nor the
scale of the potential failures cannot be specified at present,
there are some old landslide scarps and linear depressions inthis area. In fact, big failure of Mt.Kumadaore by the 1858
earthquake at the left bank of the Yukawa (see Fig.2) isrecorded in old documents. Another reason of unstableness of
this area is the intensive alteration in the granodiorite whichhave been confirmed at the chance of maintenance work for
the Arimine tunnel, and the overlying lava of the volcanicstage 1b is making a role of water storage at present.
There are many other big and small unstable slopes inand around the caldera. For instance, at the vicinity of thewestern foot of Mt.Jyodoyama where is close to the Murodo,
some precursors of primary landslide are indicated by Nozaki(2014). They must contribute to the demolition of the caldera
and future disasters, therefore more comprehensive geologicalinvestigations are strongly demanded as a view point ofdisaster-risk reduction in and around the Tateyama caldera.

Acknowledgements
Sincere appreciation is expressed to research membersof the Tateyama Caldera Sabo Museum and all those who
gave the author many chances of field survey or advices andcontributed information, both published and unpublished,with which this paper could not have been written. To list allcontributors would be impossible.
References
Nozaki T. and Kikukawa S. (2012): History of Tateyama
Caldera and the deep-seated landslides - Tombi-doro andKunimidoro - Jour. Japan Landslide Soc. 49-4, pp.44-51. (inJapanese)
Nozaki T. and Kikukawa S. (2014): Tombi-doro andKunimidoro - Deep-seated landslides related to theformation of Tateyama-Caldera and their mechanism -. Bull.
Tateyama Caldera Sabo Museum, No.13, pp.1-16. (inJapanese)

6.

Conclusions
The author started the geological survey for the analysisof mechanism of the Ootombi-kuzure and Tombi-doro
several years ago. After that, his interest extended to the
pre-historical Kunimi-doro distributed at the upper reaches of
Yukawa, and then reached to the Kunimi landslide located at
the higher portion of the north bank of Yukawa-dani, andfinally to the Dashihara landslide overlain by Tombi-doro.
Conclusions resulted from these investigations are as follows.
The primary cause of the Ootombi-kuzure triggered by
the 1858 earthquake, which was generated by the active
Atotsugawa fault, was the fragile basement rocks deteriorated
by the hydrothermal alteration. It was facilitated with the aidof gently tilted discontinuities and/or clayey deteriorated
zones as a part of sliding surface.
The potential sliding surface of the Dashihara landslide
and the Kunimi landslide must have been the clay layer due tothe past hydrothermal alterations, which was intercalated
between the lower Yukawadani-volcanic-rocks and the
granodiorite. Both of the triggering cause are unknown, buthigh possibility of past earthquakes generated by the
Atosugawa fault system. Kunimi-doro might have occurredalmost simultaneously following its mother Kunimi landslide
around 30,000 years ago.

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