https://doi.org/10.20965/jdr.2021.p0646
Tung, B. D. et al.

Paper:

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –Bui Duc Tung∗1 , Ngoc Ha Do∗2 , Nguyen Kim Thanh∗3 , Le Hong Luong∗3 ,Osamu Watanabe∗4 , Kazunori Hayashi∗5, Akihiko Wakai∗6 , and Shinro Abe∗5,†∗1

GEOS Construction Technology Consulting JSC
141 Duong Van Be Street, Vinh Tuy Ward, Hai Ba Trung District, Hanoi, Vietnam∗2 University of Yamanashi, Yamanashi, Japan∗3 Institute of Transport Science and Technology (ITST), Ministry of Transport of Vietnam, Hanoi, Vietnam∗4 Suimonkikaku LLC, Miyagi, Japan∗5 Okuyama Boring Co., Ltd., Akita, Japan† Corresponding author, E-mail: abeshinro@gmail.com∗6 Gunma University, Gunma, Japan[Received November 29, 2020; accepted April 12, 2021]

Landslide damage has been reported in many limestone areas in Europe, where the population lives close
to limestone areas, and in Guilin in southern China
and Ha Long in Vietnam, which are known for theirunique limestone landscapes. There are few studies
on the mechanism and type of landslide motion in
and around such limestone areas. The lack of basic
data is a problem for risk assessment and countermeasures in limestone areas. In this study, we summarized the causes and mechanisms of landslide occurrence, including geology and groundwater, focusing on six landslides that occurred in limestone areas
in northern Vietnam, and classified them into six typesof landslide movement. In the case of Japan, the occurrence of landslides in limestone areas is rare despite the wide distribution of limestone, and it is difficult to classify the type of movement. Differencesin the landslide mechanisms are caused by the difference between limestones generated in the pelagic environment of Japan and limestones developed along the
Tethys Sea coast, which are mixed with pelitic rocks as
shallow-water sediments in Europe, China, and Vietnam. It is necessary to elucidate the relationship between landslides and the formation environment andsedimentary characteristics of limestone as an accretionary prism based on comparisons of a wide rangeof cases in future studies.

Keywords: limestone, landslide, karst, landslide movement type, groundwater

1. Introduction
Limestone is a carbonite rock, composed of carbonate
minerals such as dolomite. It is a biogenic sedimentaryrock that contains more than 50% calcium CaCO3 and has
a calcareous shell, composed largely of corals and foraminifera. The distribution of limestones is widespread in
the Northern Hemisphere, especially in North America,
Europe, and Asia (Fig. 1). Limestone is easily dissolved
in rainwater containing carbon dioxide, and is known tohave features, such as karst topography, due to weatheringand erosion, and a large quantity of groundwater flowing
through its cavities. Landslide hazards in limestone areas occur frequently in the vicinity of mountain ranges
in Europe and North America, and in a wide limestone
area from southern China to the Indochina Peninsula [2].
In recent years, the areas where slope disasters have occurred frequently in the Asian monsoon region have overlapped with these limestone areas, and the relationship between these disasters and meteorological conditions, suchas heavy rainfall, has attracted attention [3]. However,there is a lack of comprehensive discussions on the geomorphological and geological mechanisms and movement types of landslides in these limestone areas, therefore, there is a lack of basic data on landslide initiation
mechanisms necessary for risk assessment (e.g., [4]) andplanning landslide countermeasures.
The purpose of this study is to clarify the kinematic
types of landslides that occur in such limestone areas,
the depositional environment of limestone that forms the
background of such landslides, the relationship in termsof deposition between limestone and pelitic rock, and the
involvement of groundwater in the limestone area as a factor in their occurrence.
The landslides we studied were mainly those in northern Vietnam [5], which we have studied in the past, as
well as those in limestone areas in Europe and southwest-

646

Journal of Disaster Research Vol.16 No.4, 2021
© Fuji Technlogy Press Ltd.

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –Fig. 1. Distribution of carbonate rocks. From Kano [1]. The
gray area indicates the distribution of carbonite rock.

ern China, which were deposited on the continental margin of the Paleo-Tethys Sea [6] during the late Paleozoic
and Mesozoic eras. We compared those areas with limestone areas in Japan, where there are few landslides despite the large distribution of limestones.

2. Definitions of Method and Terms

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Fig. 2. Limestone distribution area and study area in northern Vietnam. The distribution of limestone and the geological structure were developed based on Khang [8]. The landslide distribution map was obtained from the Department of
Geology and Minerals of Vietnam [9]. The gray points oflandslides are not classified in terms of scale and may include small-scale landslides such as boulders. Other points
indicate landslides with a landslide volume of 1,000 m3 orlarger.

2.1. Method
Discussions on landslides in this study are basedon case studies of landslides in northern Vietnam, theMt. Reschberg and Rindberg landslides in Austria, andthe literature, which was surveyed in the field from 2010
to 2019. In this study, landslides in the limestone area
caused by earthquakes with different generation mechanisms were excluded. Since there is no data on limestone
alone, the limestone distribution maps used are all basedon carbonite rock or karst area distribution maps instead.
The age of the geological features in the landslide area in
Vietnam is based on a 1:200,000 geological map [7].
In order to understand the relationship between groundwater in the limestone area and surface or groundwaterin the pelitic rock zone bordered by faults in Vietnam,
groundwater analysis was conducted in the landslide area
(B in Fig. 2) in the Mac Chau region, one of the study
sites. Water temperature, pH, and electrical conductivity were measured at the site. The samples were filteredthrough a 0.45 µ m membrane filter and brought backin polyethylene containers for an analysis of the major
ions and dissolved silicic acid. Major cations (Na+ , K+ ,Ca2+ , and Mg2+ ) were analyzed by atomic absorption
spectrophotometry, anions (Cl− , NO3− , and SO2−4 ) by ion
chromatography, alkalinity (equivalent to HCO3− concentration) by acid titration using the Gran method as theendpoint determination method [10], and dissolved silicic acid (silica SiO2 ) by molybdenum yellow absorption
spectrophotometry. The analytical results were organized
in stiff diagrams and tri-linear diagrams, and PHREEQC(an earth science code developed by the USGS) wasused to calculate the equilibrium partial pressure of carbon dioxide (PCO2 ) in groundwater and the saturation inJournal of Disaster Research Vol.16 No.4, 2021

dex (SIc) for calcite.

2.2. Terms
Landslides occurring in and around the limestone area
are hereafter referred to as “limestone area landslides.”The term “pelitic rock” used in this study is a generic term
for mudstone, marl, shale, or muddy schist intercalated inor faulted with limestone.

3. Case Examples of Landslides
3.1. Case Examples of Landslides in Vietnam
The northern part of Vietnam has many mountainous
slopes, and landslide disasters caused by typhoons andheavy rainfall during the rainy season are common annually. Most landslides occur in the weathered areas ofpelitic rock and granitic rocks, and few of them occur inlimestone areas. In recent years, however, landslides haveoccurred frequently along the national roads parallel tothe Laotian border in northern Vietnam, along the Song
Ma suture zone and the Red River fault, which was thecollision site of the South China and Indochina cratons in
the late Paleozoic and early Mesozoic (Fig. 2).
These landslides are classified into two types: those occurring in the pelitic rock distribution area, which meetsthe limestone with a fault (A, B, C, and D in Fig. 2), andthose occurring in the limestone layer where the stratigraphic dip is more than 70◦ (E and F in Fig. 2).

647

Tung, B. D. et al.

Residence

Limestone
Pelitic rockLandslide
Spring water

cave, crack with groundwater

Road

ce
rfa
su
e
lid

Fault
Fa

S

River

Fig. 5. Main scarp of landslide at site B (Moc Chau region).
The arrow indicates landslide movement direction.
Fig. 3. Geomorphological and geological characteristics oflandslides (A, B, C, and D in Fig. 2) along the Song Ma
suture zone in northern Vietnam. Landslides occur in thepelitic rock zone, which is in contact with limestone at afault.

Fig. 4. Site A: Don Ban region – Landslide toe area –.

3.1.1. Landslides Occurring in a Pelitic Rock Distribution Area That Is in Contact with Limestone
at a Fault
As shown in Fig. 3, all these landslides occurred in the
Mesozoic pelitic rock distribution area, which is in contact at a fault with the Late Paleozoic to Early Mesozoic
limestone.
In the Don Ban region (A in Fig. 2), a 40 m wide area
collapsed in 2012 (Fig. 4), killing two people on the national road. About 200 m north of this point, cracks anddeformation were observed on the slope of the road thatwas being improved in 2007. About 100 m to the north,another landform above the slope in a village shows tracesof past landslide occurrence. Shale and crystalline schist
are distributed on the road slope, and at the top of theslope Triassic limestone, which is in contact with thesestrata at a fault, forms a north-south ridge. Limestone648

masses with stalactites are scattered under the steep limestone cliffs. During heavy rainfall, a large quantity of surface water flows down from the limestone area to the roadslope, which is a major cause of landslide occurrence.
In the Moc Chau region (B in Fig. 2), houses in thevillage were deformed and roads were cracked during theheavy rains in 2017. The Triassic limestone in the uppermost part of the slope is in contact, at a fault, with the
mudstone and siltstone in the middle and lower part of theslope, and the limestone area is bordered by groundwater
springs from cavities. The slope is covered with rainwater gullies, and some of them are deeply scoured to form
streams. The slump type slides (Fig. 5) of 10–20 m width,
occurring from the road slope to the village area, are all
moving toward the stream formed by such scouring.
In 2010 and 2012, landslides occurred at site C in the
Muong Lay region (C and D in Fig. 2), with a width ofabout 300 m and a length of about 100 m, due to roadwidening. A part of the landslide’s moving soil mass hit
the wall of a hospital located at the bottom of the slope
and stopped. The Devonian limestone at the top of theslope is connected to the pelitic rock (siltstone, shale, andcrystalline schist) from the middle to the bottom of theslope by a fault. The slope is dotted with springs, andsome basalt boulders are observed. The landslide occurs
in muddy rock, and a main scarp can be seen at the head
and a slip surface at the toe (Fig. 6).
In addition, a landslide with a width and length ofabout 300 m occurred at site D, about 10 km south ofsite C, during heavy rains in 2011, burying a road andpart of a river. The geology of the landslide slope consists of shale and siltstone as in site C, and limestone is
distributed at the top of the slope (Fig. 7). The landslide’s
moving soil mass is mixed with shale, siltstone, and limestone gravel containing stalactites.
3.1.2. Landslides That Occur in the Limestone Layerwith a Steep Geological Slope
The landslide that occurred in the early morning of
October 12, 2017 at site E (Khanh Village region) in
Fig. 2, was about 120 m high, buried 4 houses, and killed
Journal of Disaster Research Vol.16 No.4, 2021

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –Landslide120m

Khangh waterfall

m
Ke

er
riv

Landslide

Fig. 6. Site C: Muong Lay region. Upper: Landslide
main scarp. The arrow indicates the direction of the slide.
Lower: Slip surface appearing at the toe of the landslide.

120m

Water fall

Limestone
Shale

River

Fault

Main crown
Limestone

Fig. 8. Landslide and geological schematic cross section
at site E (Khanh waterfall). Upper: Panoramic view. The
slide’s width was about 200 m. Lower: Geological schematiccross section. The bold arrow indicates the direction of landslide movement.

Shale, siltstoneFig. 7. Main scarp at site D. The arrow indicates the direction of landslide movement.

18 people. The collapsed soil of the area, including the
Khanh waterfall which is also known as a tourist attraction, crossed the river flowing down the lower slope andovercame the hill on the other side (left bank), with aheight of about 30 m, to reach the paddy field (Fig. 8).
As a result, the Khanh waterfall has now receded by 40–
50 m. The geology of the area consists of Mesozoic Triassic limestone and shale. The strike of the stratum is
N10◦ –40◦ W with a dip of 70◦ –80◦ E, which is close tovertical (Fig. 8).
The Ha Long region (F in Fig. 2), which is well known
as a limestone tower karst landscape, has experienced
many landslides in recent years. The geology of the area
consists of shales with coal, gray massive limestones, siltstones, and conglomerates of Carboniferous to Triassic.
This site is on the extension line of the Red River fault(Fig. 2). The landslide, which occurred in 2017 on a slope
under road construction, with a width of about 70 m andJournal of Disaster Research Vol.16 No.4, 2021

a length of about 120 m, is located on the synclinal axisof the folding structure, and pelitic rock (coal, shale, andsiltstone) in a wedge shape, sandwiched by limestone layers on both sides, was moved to the front. In the middle
and lower areas of the landslide, several springs can beobserved from the cavity in the limestone layer. The main
reasons for the occurrence of landslides are the existenceof pelitic rock layers that are fractured into wedges dueto the folding structure, and the large quantity of springwater from the cavity of the limestone area during heavy
rainfall (Fig. 9).
3.1.3. Relationship Between Groundwater in Limestone and Landslides
All the aforementioned landslides in northern Vietnam
seem to be influenced by limestone groundwater. In particular, the groundwater in the limestone behind the slopesat A–D may play an important role in causing the landslide of pelitic rock on the lower part of the slope. Therefore, we analyzed the groundwater quality of limestone
and pelitic rock (Fig. 10) in the Moc Chau region (B in
Fig. 2) [5].
All the springs are rich in Ca2+ ion and HCO−
3 ion
and are classified as “alkaline-earth metals, bicarbonatetype” (Fig. 11). Of the six locations, G015 and G016 arespring water from cracks in the limestone or spring water649

Tung, B. D. et al.

G018: Spring water

G015: Spring water(Limestone area)
meq/L

meq/L

10

10

Cl-

Na++K+

Ca2+

HCO3-

Ca2+

HCO3-

Mg2+

SO42-,(NO3-)

Mg2+

SO42-,(NO3-)

10

5

0

5

Na++K+

G012: Spring water(Landslide area)

5

0

5

G016: Spring water(Limestone area)
meq/L

0

5

10

10

Cl-

Na++K+

Ca2+

HCO3-

Ca2+

HCO3-

Mg2+

SO42-,(NO3-)

Mg2+

SO42-,(NO3-)

Na++K+

5

meq/L

10

Cl-

Na++K+

Ca2+

HCO3-

Ca2+

HCO3-

Mg2+

SO42-,(NO3-)

Mg2+

SO42-,(NO3-)

0

5

0

100

Cl -

R6

Sampling point for water examinaion

Fig. 10. Groundwater test sample collection point in the
Moc Chau region (site B).

from the area behind the limestone. The other locations,
G012, G018, and G021, are all springs collected from theslope of pelitic rock, and G010 is water from a small river
flowing down the slope of pelitic rock. The groundwaterfrom the limestone area has higher electrical conductivity
than the groundwater in the mudstone zone (i.e., more dis650

CO ₃
CO2₃+
H

2+

Mg

SO 2₄+
Cl -

w
at
er
G
ro
un
d
er
300m

ϩ

2-

Ϫ

₄
SO

Riv
Landslide

0

2+

g

GO15
GO12

+M

Fault

N
GO21

0 100

+
++ K
Na

2+

g
+M

0

Ϭ

0

Ϭ

100

0
Ca 2+

CATIONS

GO16

Ϫ

100 0

2+

Ϩ

Ca

GO15
GO16

GO18

Ϭ

0

GO12
GO21

Limestone area

2+

Ϩ

GO18

0
100

Mudsone areaϫCa

(Ⅴ: Mixed type)

ϫ

10
Cl-

Ⅰ：alkaline-earth metals(Ca + ; Mg² + ) bicarbonate typeⅡ : alkaline(Na+ ; K + ) bicarbonate type+
Ⅲ：alkaline(Na+ ; K ）chloride type
Ⅳ：alkaline-earth metals(Ca + ; Mg² + ) bicarbonate type

GO10

5

SO 2₄+

bo
dy

5

100

Fig. 9. Panoramic view and modeled geological crosssections of site F (Ha Long region). The dashed line in thephoto indicates the landslide area and the arrow indicates the
direction of landslide movement.

10

10

5

Na++K+

Conglomerate Limestone Shale with coal
Siltstone-Silty shale

5

G010: River
No.1 water

meq/L

La
nd
sl
id
e

0

Cl-

G021: Spring water (water supply)10

Springg water

10
Cl-

meq/L

10

5

100 100
0
0

Cl

-

100

0

ANIONS

Fig. 11.
Stiff diagrams (upper) and tri-linear diagram (lower). Modified from Tung et al. [5].

solved ions), but has low SiO2 content (Fig. 12). Fig. 13
shows the relationship between the HCO−
3 ion concentration and the concentrations of the major cations (Ca2+ ion
and Mg2+ ion). The fact that both are plotted on a straightline passing through the origin suggests that dissolutionof minerals by dissolved CO2 (chemical weathering) is
involved in the formation of the water quality of these
springs.
. . . . (1)
CaCO3 + H2 O + CO2 → Ca2+ + 2HCO−
3(Calcite)
CaAl2 Si2 O8 + 2CO2 + 3H2 O(Ca-feldspar)→ Al2 Si2 O5 (OH)4 + Ca2+ + 2HCO−
3 . . . (2)(Kaolinite)
The lower SiO2 content in the limestone area, compared to that in the pelitic rock slope, can be explainedby the smaller contribution of chemical weathering offeldspars, as shown in Eq. (2).
Table 1 shows the equilibrium partial pressure ofcarbon dioxide (SIc) in groundwater, calculated using
PHREEQC (USGS). The carbon dioxide concentration ishigher (0.04–2.2%) in soil than in air (0.04%) [11]. In
some places, such as near faults, the carbon dioxide concentration is even higher due to the carbon dioxide supply
from deeper layers. The spring from a crack of limestone (G015) is characterized by a high PCO2 of 6.3%.
The equilibrium partial pressure of carbon dioxide in the
Journal of Disaster Research Vol.16 No.4, 2021

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –(μS/cm)
1000
800
600

EC

400
200
0

(mg/L)
50
40

GO12

GO15

GO16

GO18

GO21

Spring water

Spring water

Spring water

Spring water

Spring water(Landslidearea)(Limestonearea)(Limestone
area)

Site

(Water supply)

SiO₂

30
20
10
0

GO12

GO15

GO16

GO18

GO21

Spring water(Landslide
area)

Spring water(Limestonearea)

Spring water(Limestonearea)

Spring water

Spring water

2+

6.80

6.3

−0.01

7.20

3.0

0.43

7.80

0.5

0.63

Site

pH

PCO2
[%]

SIc

GO21: Spring water (Water supply)

G012: Spring water(Landslide area)

6.77

7.9

0.00

GO16: Spring water (Limestone area)

G018: Spring water

7.16

2.0

0.00

GO15: Spring water (Limestone area)+ Mg 〔meq/L〕

SIc

GO12: Spring water (Landslide area)

92+

G018: Spring water

PCO2
[%]

Table 2. CO2 equilibrium partial pressure calculated under
the calcite dissolution equilibrium condition (SIc = 0) (Simulation result from PHREEQC).

10

Ca

G015: Spring water(Limestone area)
G012: Spring water(Landslide area)pH(water supply)

Fig. 12. EC and silica concentration.

8
7

Table 1. Carbon dioxide equilibrium partial pressure ofspring water.

6

GO10: River water
GO18: Spring water

5

with the groundwater recharged by rainfall on the pelitic
rock slope, and undergoing shallow flow (G018), and thegroundwater with a relatively high carbon dioxide concentration, recharged by the limestone distribution area
behind it.

4
3
2
1
0
0

1

2

3

4
6
5
7
HCO 3〔meq/L〕

8

9

10

Fig. 13. Relationship between alkalinity and divalent cation
concentration.

spring water is low because the water is in the process ofdegassing and is close to the atmospheric partial pressureof carbon dioxide (0.04%). Since the solubility of calcite is proportional to the cube root of CO2 concentration,
the SIc increases with degassing, and both slope springs
are supersaturated with calcite (SIc > 0). Table 2 shows
the results of the calculation of PCO2 where SIc = 0. Thisis an estimation of the state before the inflow (before degassing). Among the spring waters from the slope of silt
and mudstone, the PCO2 of the landslide edge spring water (G012) was found to be close to that of the spring waterfrom limestone (G015). G018, on the other hand, showeda value (2%) normally considered as that of groundwaterin soil.
Among the three springs from the pelitic rock, thesprings with a high equilibrium partial pressure of carbon dioxide (G012 and G021) are plotted between G018
and the limestone groundwater group in the Tri-linear diagram of Fig. 6. This indicates that the mixing of these
two groups is a possible explanation. In addition, these
two springs are also used as a water supply source, andthe flow rate is relatively stable. Therefore, the groundwater on the slope of the pelitic rock is likely to be mixed
Journal of Disaster Research Vol.16 No.4, 2021

3.2. Landslides in Places Other than Vietnam
3.2.1. Examples in Europe
Landslides in the limestone zone in Europe are mostly
found in the Alps, the Italian Peninsula, and the Pyreneesof the Iberian Peninsula to the Mediterranean coast. Theselandslides mostly tend to occur on the margins of the limestone area rather than on the limestone (Fig. 14).
The most characteristic landslides in the European
limestone area are lateral spread type landslides, such as
the Mt. Reschberg landslide in Austria [14] (Figs. 15
and 16) and the Moute Verna landslide in Italy [16]. Theselateral landslides were caused by the sinking of soft pelitic
rock in the lower layer due to loading by limestone in
the upper layer. In addition to the occurrence of lateral
spread, landslides of the debris flow type, in which thelimestone itself overturns and the pelitic rock mixes withthe rock masses caused by falling rocks, have occurred.
Such landslides have also been reported in the suburban
Algiers landslide in North Africa [17] and at Turtle Mountain in Canada [18].
In the case of pelitic rocks, such as marl, shale, andmuddy schist intercalated in limestone layers, or in thecase of their intercalation, translational rock slides haveoccurred, such as the Vaiont dam landslide in Italy [19]which claimed more than 2,000 victims in 1963, or the
Rindberg landslide in Austria [14], where Cretaceous
limestone and pelitic rock moved on a scale of 2,400 m
in length, 700 m in width, and a maximum slip surface
651

Tung, B. D. et al.

Limestone

Toppling

slump
w

-flo

h
art

Spread

E

Ear

th-f

low

Shale, Marl

Fig. 16. Lateral spread and debris flow type landslides in
the Stambach and Sandling landslides. Created from Upper
Austrian Sabo Bureau [15].

1000 km0Landslide

Fig. 17. Panoramic view of the Rindberg landslide. From
the Upper Austrian Sabo Bureau [15].

Huttenckaim
1200

00

13

Ea

rth

flo

w

Fig. 14. Distribution of carbonite rock (blue) and landslides (red dots) in Europe. Most damaging landslide cases
from 1995–2014 and 2016. Adapted from Haque et al. [12],carbonite rock distribution from Goldscheider [13].

am

ba

ch

Fig. 18. Moving rock body exposed on the mid-slope of the
Rindberg landslide.

St

Mt.Raschberg
1487m

14

00

N

depth of more than 80 m (estimated at 120 m) (Figs. 17
and 18).

1300Pichlernlow1201100 0Rehkogl

rth
f

1000

ng
dli
Sa
n

800

Ea

900

70

0

500m

Fig. 15.
Stambach and Sandling landslides on
Mt. Raschberg (the plane diagram is based on the Upper
Austrian Sabo Bureau [15] with some modifications and additions).

652

3.2.2. Examples in China
In the southern part of China, there are extensive limestone belts, including in scenic areas such as Guilin. The
landslides in the limestone belt are distributed aroundthe limestone distribution areas in Sichuan, Yunnan, andGuizhou provinces (Fig. 19). However, the occurrence of
limestone-related landslides is not as common as those inother formations in China [22, 23]. These landslides haveslightly different moving types due to the location of thecoal and shale formations intercalated in the limestone;
however, limestone rock slides of more than 100 m haveoccurred, as in the case of the landslide represented by the
Wangxia rock slump [24] (Fig. 20). In addition, several
cases of limestone landslides, such as the Xintan landslide [23, 26] and Guang’an Village landslide [25], havebeen reported to flow as debris flows over long distances
Journal of Disaster Research Vol.16 No.4, 2021

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –1000 kmLandslide
Karst area

Fig. 19. Distribution of karsts and landslides in China. Karst
data is taken from Liu and Zhao [20]. Landslides are catastrophic ones since the 20th century by Huang and Li [21](earthquake landslides are not included).

1000-1200m

Lomestone
Shale, mudstone

300km

0

Fig. 21. Designated landslide areas in Japan (red dots) andlimestone distribution (blue). The arrow indicates the pointof Fig. 22. Araiba et al. [28], Urushibara-Yoshino [29].

Coal seamLandslide deposit
1000-1500m

Fig. 20. Conceptual diagram based on landslide cases inlimestone area in southeast China. Created by reference
to Feng et al. [24], Wang et al. [25], Luo [26], and Wen
et al. [23].

Spring water0(1.5 km or more) on the lower slopes composed of shaleand sandstone (Fig. 20).
3.2.3. Examples in Japan
Limestones as an accretionary prism of seamount origin [27] are widely distributed across the Japanese Islands(Fig. 21). The number of landslides in the limestone area
in Japan is very small, although there were 6,785 designated landslides in 1998 [28] (Fig. 21). Only a few
cases have been reported, such as the late Paleozoic to
mid-Mesozoic limestone area landslide in the Shikoku
region (Fig. 22) [30], which is similar to the landslide
shape along the Song Ma suture zone in northern Vietnam (Fig. 3). Others include the colluvial landslide withslip surface on the weathered part of the Paleozoic limestone in the Hokuriku region [31], and the erosion landslide with Pliocene to Pleistocene mixed mudstones andJournal of Disaster Research Vol.16 No.4, 2021

sit
po
de
l
a
vi
llu
co
e
ce
lat
d s surfa
e
r
e
e
h
t
d
a
Sli Slate
We

Limestone

Fault

50 m

Fig. 22. Example of limestone area landslide in Shikoku,
Japan. Arrow point in Fig. 21 (modified from Utsunomiya
et al. [30]).

mixed limestone in Okinawa, Japan [32]. There are nocase reports for a slip surface of pelitic rock sandwiched
between limestones, as seen in the aforementioned casesin Europe, China, and Vietnam.

4. Discussion
In the case of limestone, which is massive and poorly
stratified, there are few cases of movement with a slip surface in the limestone except for rock falls and rock col653

Tung, B. D. et al.

Fig. 23. Limestone area landslide types in Europe, China, Vietnam, and Japan.

lapses. Most of the landslides in the limestone areas occur as landslides with slip surfaces in mudstone or coalbeds intercalated or interlayered with the limestone, or as
landslides of pelitic rock in the pelitic rock zone near the
limestone. If we summarize the shapes and movementsof landslides in the limestone areas of various regions,654

we find that in Vietnam, most landslides occur as slump
type landslides (Fig. 23, A) in the pelitic rock distributionarea, where the limestone is faulted. In Vietnam, otherunique types of landslides include a large-scale collapseof a waterfall formed during the development of a riverwhich erodes the boundary between limestone and pelitic

Journal of Disaster Research Vol.16 No.4, 2021

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –rock (B in Fig. 23), and a wedge-type slide of the pelitic
rock portion where limestone and pelitic rock meet at ahigh angle due to faulting and folding (C in Fig. 23). The
common causes for the landslides in these limestone areas include erosion and the softening of muddy ground byspring water and surface water originating from groundwater flowing through limestone cavities, and groundwater supply into the landslide area.
In Europe, the pelitic rock is deformed by the load oflimestone covering it in the form of cap rock, causing lateral spreading and then a transition to a flow type landslide (D in Fig. 23) or to a rockslide on a sliding surfaceof the pelitic rock sandwiched between limestones (E inFig. 23).
In China, toppling and rockslide along the pelitic rocklayer, intercalated in the thick limestone layer, as well as
the debris flow of a mixture of limestone masses collapsed
down the cliff and pelitic rocks in the lower part of thecliff (F of Fig. 23), are commonly observed.
The contact between limestone and pelitic rock, which
influences the landslide shape, is formed by the depositional environment and geological structure of the geological age.
The limestones in the European Alps are frequently interrupted by pelitic rocks of Paleo-Tethys and continental origin. The stratum is significantly folding but relatively continuous, which provides a geological predisposition for the occurrence of large-scale rockslides along
the bedding plane and lateral spread type landslides.
The limestone area in south China, several kilometersin thickness, is also mixed with continental clastic debris
and pelitic rock from the Paleo-Tethys Sea. Currently
however, there are more reports of limestone collapses
bounded by pelitic rocks, and debris flows caused by collapsed limestones and pelitic rocks, than of rockslides
such as those in the European Alps. Most of the landslides in and around the limestones in northern Vietnam
are located in the areas where faults and folding structures are developed on the tectonic line (suture zone and
Red River fault) where the South China and Indochina
blocks collided across the Tethys Sea [33]. Such geological structures are geologically predisposed to landslides
in the pelitic rock zone bordered at faults by limestones,
and to wedge-like movement of the pelitic rock between
limestones in folding structures.
In this study, we mainly focus on limestone area landslides at the collision site of continental massifs acrossthe Tethys Sea, but we also attempt to compare them withlandslides in Japan, where pelagic limestones are widelydistributed. As a result, we found that Japanese limestones, deposited in the pelagic environment with little
sediment supply from the continent, are characterized bya high purity of calcium carbonate, are lumpy and poorly
stratified. This is why the number of slip cases in limestone areas in Japan is smaller than those in Europe andAsia.

Journal of Disaster Research Vol.16 No.4, 2021

5. Conclusions
The landslide shapes and movement types in the limestone areas discussed in this paper can be roughly classified as follows:• Landslides of the limestone itself, such as a rock fall,

toppling, or cavity collapse along a crack in the limestone.
• Rockslide, in which the slip surface is a muddy stratum that alternates with limestone or forms a thinlayer.
• Landslides that occur as a lateral spread caused by
the deformation of pelitic rock at the base due to theload of limestone, as well as landslides that occur
as earth flow or debris flow of limestone and peliticrock.
• Slump type landslides that occur in pelitic rock whengroundwater is supplied from limestone with which
the pelitic rock is in contact at a fault.
• Wedge type slides of pelitic rock in contact withlimestone due to folding or fault structure.
Landslides occurring in limestone areas often occur atthe margins of the limestone rather than the limestone itself. A common cause is the influence of abundant surface
water and groundwater flowing down the limestone.
The landslides described above occur with different
types of landslide movement, based on the geology andgeological structure formed under various conditions, including: where corals developed along the continental
margin during the mid-Paleozoic and early Mesozoic,
with continentally detritus flowing into the Tethys Sea
and pelitic rock of shallow-water sediments are sheared,
fractured, and deposited as accretionary prisms by the
movement and collision of land masses, or where they arefolded and ridden up.
The limestones distributed across Japan are highly purecalcium carbonate limestones which were formed in apelagic environment with little sediment supply from thecontinent, and are characterized by massive and poorly
stratified accretionary prisms, which is the reason for the
low occurrence of landslides.
In the future, when assessing the risk of slopes in limestone areas, attention should be paid to the pelitic rock incontact with the limestone from the viewpoint of geology
and geological structure, and to the edge of the limestone
from the viewpoint of topography. In addition, it is necessary to pay attention to the surface water and groundwater supplied to the slope from the limestone as a causeof landslides when considering countermeasure construction.
Limestone zones are widely distributed in other continents, in addition to the areas targeted in this study, andmany of them are located outside human population areas. It is assumed that landslides with various types of
motion, other than those mentioned above, probably occur in these areas. In the future, it is necessary to clarify
the relationship between the limestone formation process,the deposit shape of the accretionary prism, and the mech655

Tung, B. D. et al.

anism of landslide occurrence based on a wide range ofcases, including pelagic cases common in Japan.
Acknowledgements
This study was discussed in the “Vietnam Landslide Practical Technology Group” of Japanese and Vietnamese researchers
in Hanoi. We would like to express our sincere gratitude toProf. Kazuhisa Yoshimura, Professor Emeritus of Kyushu University, for his many insights on groundwater in limestone areas.

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Journal of Disaster Research Vol.16 No.4, 2021

Geometry and the Mechanism of Landslide Occurrence
in a Limestone Area – Case Examples of Landslides
in Vietnam and from Europe, China, and Japan –Name:
Bui Duc Tung

Name:
Osamu Watanabe

Affiliation:
Civil Engineer, JGC Vietnam Co., Ltd.
Civil Engineer, GeoS Consultant JSC
Geotechnical Engineer, SMEC Vietnam JSC

Affiliation:
Suimonkikaku LLC

Address:
2-17-3-205 Izumi-chuo, Izumi-ku, Sendai, Miyagi 981-3133, Japan

Address:
Landmark 72 Tower, Pham Hung Street, Nam Tu Liem District, Hanoi,
Vietnam

Selected Publications:• “A preliminary study on the mechanism of landslide in limestone
formation area in Son La. Northern Vietnam,” Proc. of 2016 Int. Conf. on
Sustainability in Civil Engineering, Geotechnical Engineering, pp. 76-80,
2016.

Name:
Kazunori Hayashi

Affiliation:
Assistant Manager, Okuyama Boring Co., Ltd.

Address:
13-18-306 Futsukamachi, Aoba-ku, Sendai, Miyagi 980-0802, Japan

Name:
Ngoc Ha Do

Affiliation:
Doctoral Course Student, University of Yamanashi
Engineer, Researcher, Institute of Transport Science and Technology(ITST)Name:
Akihiko Wakai

Address:
4-4-37 Takeda, Kofu, Yamanashi 400-8510, Japan (University of
Yamanashi)
1252 Lang Street, Dong Da District, Hanoi, Vietnam (ITST)

Affiliation:
Professor, Gunma University

Address:
1-5-1 Tenjincho, Kiryu, Gunma 376-8515, Japan

Name:
Nguyen Kim Thanh

Name:
Shinro Abe

Affiliation:
Ph.D. Student, Tohoku Gakuin University
Researcher, Institute of Transport Science and Technology (ITST)

Affiliation:

Address:

Address:

1252 Lang Street, Dong Da District, Hanoi, Vietnam

Technical Advisor, Okuyama Boring Co., Ltd.
10-39 Shinmei-cho, Yokote, Akita 013-0046, JapanName:
Le Hong Luong

Affiliation:
Institute of Transport Science and Technology (ITST)

Address:
1252 Lang Street, Dong Da District, Hanoi, Vietnam

Journal of Disaster Research Vol.16 No.4, 2021

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