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SAARC Workshop on
Landslide Risk Management in South Asia
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Messages v
Background Paper 1
SAARC Disaster Management Centre, New Delhi
Geomorphology and Landslide Potential of the Bamiyan
Valley in Afghanistan 53
Giuseoppe Delmonaco, Claudio Margottini
Landslide Vulnerability of Bangladesh Hills and Sustainable
Management Options: A Case Study of 2007 Landslide in Chittagong City 61
Amanullah Bin Mahmood, Mamunul H. Khan
Landslides in Bhutan 73
Karma Kuenza, Yeshi Dorji, Dorji Wangda
Importance of Earthquake Induced Landslides in
Landslide Hazard Mapping 81
R. K. Bhandari
An Overview of Landslide Hazard in Nepal Himalaya 91
Deepak Chamlagain, Sajana Suwal
Incipient Landslides in the Jhelum Valley, Pakistan
Following the 8th October 2005 Earthquake 107
David Petley, Stuart Dunning, Nicholas Rosser, Allah Bahksh Kausar
Overview and Advancement in Landslide Risk
Management in Sri Lanka 117
R. M. S. Bandara
Contents
SAARC Workshop on
Landslide Risk Management in South Asia
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Geomorphology and Landslide Potential of the
Bamiyan Valley, Afghanistan
Giuseoppe Delmonaco, Claudio Margottini
APAT - Italian Agency for Environmental Protection and for Technical Services - Rome, Italy
Abstract
The present work reports geomorphological and geotechnical investigations carried out in the UNES-
CO site of the Bamiyan valley (Central Afghanistan) in 2007 in order to reconstruct active deformation
processes and geomorphological hazards affecting Cultural Heritage. The site is known worldwide
for two standing giant statues of Buddha destroyed by Taliban in March 2001. The geomorphologi-
cal fi eld survey has reconstructed the main active geomorphological processes along the cliff area
mainly related to superfi cial waters (e.g. erosion, infi ltration along joints, accumulation of mud/debris)
and slope deformations (e.g. toppling, rock falls, rock slides, jointing). The geomorphological survey
has been integrated with geotechnical, structural and kinematic analyses concentrated in 17 distinct
sections of the cliff where geological processes were more prominent. This to detect and investigate
potential failure modes of the jointed rock masses forming the Bamyian cliff. The kinematic analysis
produced different results for the various slope failure modes analysed according to local structural
and geomorphological characteristics of the cliff. A geomorphological map reporting the main pro-
cesses surveyed in the area has been produced.
Keywords: Geomorphology, Slope instability, structural analysis, landslide kinematics,
Bamiyan
Geological Setting
The Bamiyan valley (Figure 1) is an intramountainous basin, subsequently fi lled with debris material
originating from the surrounding mountain ranges (Lang, 1971; Reineke, 2006). The Neogene near-hor-
izontally bedded sediments can be distinguished into four strata. Starting with the Eocene Dokani For-
mation (>80m sandy carbonate and anhydrite) and the Zohak Formation (>1000m red conglomerate),
the so called Buddha Formation is deposited in the Oligocene and built up by >70m yellow-brown
pelite, sandstone, conglomerate and some volcanic material. The top is composed by the Miocene
Ghulgola Formation (>200m sandstone, clay and lacustrine carbonate) and the Pliocene Khwaja-Ghar
Formation (ca. 200m travertine, sandstone and conglomerate. The Qal’acah Formation is almost con-
temporary to the Buddha Formation and refl ects a detritic facies on the slope of a volcano (Lang, 1972).
At north and south of the fault lines of the tectonic graben, red clayey soils formed by metamorphic
contact can be found. Along these fault lines, volcanic activity can be recognized. This may have modi-
fi ed (fritted) the surrounding sediments and changed their colour into red.
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Geomorphology and Landslide Potential
of the Bamiyan Valley, Afghanistan
From the late Pliocene to the end of Pleistocene (Reineke, 2006) the Neogene sediments have been
incised by fl uvio-glacial erosion. Alternating warm and cold periods lead to changing conditions be-
tween accumulation and erosion, so that different Quaternary terraces developed.
The cliff and niches have been
excavated into the so called
Buddha Formation and are
composed by alternance of con-
glomerate and siltstone (yellow
at the bottom and red in the
middle of the cliff) with some
pelite, sandstone and volcanic
material. The conglomerate is
the predominant material in
the cliff and presents a moder-
ate cohesion The differentiated
grain size distribution (from
conglomerate to clay) is clearly
demonstrating a not selective
depositional environment, with high energy (fl ood plain). The siltstone exhibits an apparent moderate
cohesion under dry conditions whereas, when saturated, the material tends to disaggregate complete-
ly. This is due, as demonstrated by mineralogical and petrographical analyses (Margottini, 2004), by the
absence of cement in the matrix. All lithotypes forming the slope are variably jointed.
Geomorphological analysis
Bamiyan is located at 2,540m elevation on the N edge of the 600-km-long EW valley along the Herat
fault, at the confl uence of three different rivers. The fl ood valley is mainly formed by fl uvial (alluvial and
alluvial fans) and slope sediments (landslide and slope deposits). Its evolution is related with various
factors such as lithological characteristics, tectonic activity, palaeoclimatic events, river and slope evo-
lution in the cliff. The cliff where the Buddha statues are located presents a general E-W orientation an
average slope inclination of ca. 85° and a total length of approx. 1,350m. The cliff can be divided into
two distinct sectors: the western side, where the West Giant Buddha statue is located, shows a N65°E
orientation with a length of approx. 820 m, whereas the eastern portion, where the East Giant Buddha
is placed, exhibits a N95°E orientation and a length of ca. 525 m. The two segments are separated by a
large alluvial cone generated by two distinct torrents fl owing into the Bamiyan river, still very active,
that have diverted the river fl ow towards SSE. The change of orientation from EW to NNE-SSW occurs
in correspondence of the torrent located at E. This confi guration is likely due to tectonic activity re-
garding the Herat fault system and local faults oriented NE-SW. The reconstruction of the geomorpho-
logical activity in the Bamiyan valley was developed with detailed fi eld surveys integrated with a kine-
matic analysis on 18 distinct sectors of the cliff in order to defi ne active and potential landslide types.
In general terms, in the area the following active processes have been recognized:
Figure 1: Geological map of Bamiyan (Lang, 1971; redrawn from Reineke, 2006)
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• Water infi ltration from the upper part of the cliff;
• Gully erosion in the upper catchment area and along the slope face;
• Accumulation of debris sediments at the toe; Mud fl ows;
• Toppling and rock-falls involving some isolated blocks;
• Rock-sliding along pre-existing joints;
• Active deformation processes with progressive opening of joints in the external part of the cliff.
Some processes, e.g. rock-falls and
stress development along joints
are affecting the niches of Bud-
dha statues, accelerated also by
the explosion of March 2001 that
destroyed the statues. The Eastern
Giant Buddha niche exhibits, at
present, the most critical stability
conditions. Recently, this area has
been partly stabilized with urgent
mitigation works. In the Western Giant Buddha site major effects were the collapse of the statue and
the consequent instability of the back side of the niche.
Landslide deposits are diffusely outcropping along the slope toe, generated by rock falls and toppling
of large conglomerate and siltstone blocks with modest run-out also evidenced by their typical sharp-
edged shape. Block volumes vary from <1m3 to >10m3 . Planar sliding deposits are diffusely outcrop-
ping at the base of the cliff and somewhat immersed and/or partially covered by the debris (Figure 2).
The top of the cliff, as well as the outer walls, are largely affected by diffuse and intense erosion of con-
glomerate and siltstone, especially in the western side of the cliff. This produces gully erosion that is
the typical landform that outcrops in the slope face and in the upper parts of the Buddha cliff.
The concentration of gullies is very high in the very small basins located on the top of the cliff area,
especially along the steep slopes of those tributaries creeks that form active debris cone when fl owing
into the Bamiyan valley.
The easily erodible soils with a weak structure like those forming the Bamiyan cliff, the absence of veg-
etation as well as climatic conditions of the area are prominent factors in accelerating this type of phe-
nomenon in the catchments located on the back of the cliff, with a typical retrogressive activity.
Recent and past landslide activity and soil erosion are the consequence of climate fl uctuations that
occurred in Central Asia from Late Pleistocene up to present (Esper et al., 2002; Kamp et al., 2004;
Bush, 2005).
Figure 2 : Debris accumulation (left) and gully erosion on the slope face of the Bamiyan cliff
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Considering the main geomorphological features briefl y described above and the long-term evolu-
tion of the cliff vs. climate and tectonic activity, three main stages have been recognized (Delmonaco &
Margottini, 2007) and briefl y described.
Stage 1: At the end of the last maximum glacial (13.5 ky BP) the rock slope experienced development
of vertical cracks and deep rock sliding phenomena due to the deepening of the valley. This resulted in
straining of rocks and development of parallel cracks and joints with E-W orientation. The intersection
of this system with the one linked to the tectonic stress, oriented at S (dip direction) generated deep
rock sliding phenomena affecting conglomerate and siltstone layers at the base of the cliff. Old land-
slides, mostly in inactive or quiescent state of activity, occurred before the human exploitation of the
slope as demonstrated by stable caves excavated in the landslide body. Nevertheless the presence of
two caves with evidence of displacement reveals the occurrence of rock slides at least after the 5-6th
century AD.
Stage 2: The sea level rise after the cold peak terminated in the Early Holocene promoted large deposi-
tion of debris and alluvial sediments. The reduction of the potential energy in the slope and a conse-
quent decrease of stress conditions concentrated at the slope toe changed landslide kinematics in the
Bamiyan cliff from deep landslides to toppling-sliding failure mode that are affecting the middle-high
sectors of the slope.
Stage 3: The so-called Little Ice Age (15th -19th centuries AD), with more humid conditions than pres-
ent, have promoted an increase of erosion and debris production from the upper catchments espe-
cially in the western sector of the cliff. In the middle of the slope, where the two segments of the cliff with
different orientations converge, the most active areas of debris production outcrops, evidenced by the
coalescent debris cones that have diverted the fl owing of the Bamiyan river through SSE. At present, arid
climate conditions with low annual rainfall amount and concentrated precipitation promote deep ero-
sion of loose sediments (e.g. gullies), mud fl ows along the channels and water infi ltration inside the slope
materials causing decrease of cohesion along the joints and acceleration of toppling/falling processes.
Landslide kinematic analysis
Structural setting analysis and potential instability fail-
ure modes of the slope-forming rocks has been under-
taken in June 2007 in order to provide a preliminary
sketch on potential morphological evolution of the cliff.
The angle for most of the rock face is approximately
80°-88°. The outcropping soft rocks present prominent
discontinuity sets whose origin, especially the joint sys-
tem parallel to the slope face, can be associated to the
geomorphological evolution of the valley as well as to
tectonic setting (Ambraseys and Bilham, 2003). This sit-
uation has caused apparent slope instability phenom-
Table 1 : List of structural stations with orientation
and global localisation
Geomorphology and Landslide Potential
of the Bamiyan Valley, Afghanistan
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Landslide Risk Management in South Asia
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ena, somewhat aggravated by the explosions
during the destruction of the Buddhist stat-
ues in 2001 around the niches areas. A total of
17 structural stations were selected by visual
inspections in the areas of the cliff where his-
torical structures (e.g. Buddha niches, external
and underground caves) display prominent or
potential instability conditions (Table 1).
The main joint orientation data in each ob-
servation point was represented with the
Schmidt equal angle stereonet and rose dia-
grams. For the selected stations, kinematic
analyses have been implemented to estimate
the potential failure modes (toppling, plane
and wedge sliding), that may develop along
the slope. This was divided into two main sec-
tors: W sector, where the Western Giant Buddha is located (stations 1-10) and the eastern side that in-
cludes the area of the Eastern Giant Buddha (stations 11-17). The two sectors displays different orienta-
tions, respectively 155/85° and 185/82°, due to tectonic effects (Figures 3 and 4).
The toppling analysis has
provided the following re-
sults (Figure 5) considering
a value of ’=30° along the
joints in siltstone materials,
as the weaker lithotypes
where higher stress condi-
tion can develop.
In general, the toppling potential seems to be higher in the W part of the cliff, especially in potential
remobilized volumes. In the E side
a potential toppling failure mode
exhibits minor potential volumes
involved due to a higher density of
fractures in the jointed mass that
presents, as well, a higher num-
ber of joint sets. The stereographic
analysis for planar failure is shown
in the Figure 6.
Figure 3 and 4 : Joints orientation sets of the W part of Bamiyan cliff (stations
1-10, above) and of the E part of Bamiyan cliff (stations 11-17, below) represented
through stereonet (left) and rose diagram (right)
Figure 5 : Results of kinematic analysis for toppling for W side (left) and E side of the cliff (middle); the ar-
rows show the region where toppling is possible (between slip limit and lower stereonet border). Toppling
evolution in the cliff (right)
Figure 6 : Results of kinematic analysis for planar sliding for W side (left) and E side of the cliff
(middle); the arrows show the region where planar sliding is possible (inside the slip limit area
and the upper friction cone line). Planar rock-slide involving an ancient cavity (right)
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Planar sliding is highly potential in both sides of the cliff, also as a secondary movement connected
with toppling failure, that, factually, determines the sliding of vertical blocks previously deformed fol-
lowing a typical toppling evolution. This occurs especially when the “pivot” of the block is located inside
a siltstone layer where the major stress is concentrated. In that case the evolution of failure is that typical
of a sliding, sometimes with the development of circular-shaped rupture surface in cohesive materials
(Mohr-Coulomb behavior of weak siltstone). Kinematic analysis for wedge failure is shown in Figure 7.
Major planes have been selected with the Terzaghi weighted mean statistical technique. In the W
side, wedge failure is possible in rock blocks delimitated by joints 1-2 (oriented respectively158°/76°
and 220°/72°) and 1-3 (158°/76° and 052°/83°). In the E side wedge failure can be promoted by joints
1-2 (172°/78° and 207°/82° oriented) and joints 1-3
(172°/78° and 227°/69°). It can be affi rmed that in the
W portion, since the most important system is the
discontinuity oriented parallel to the slope, this kind
of failure mode is very diffi cult to occur, since this
system primarily produces rock falls and toppling
phenomena. As a matter of fact, no special evidence
of wedge potential, although theoretically possible,
has been surveyed in this area. On the contrary, the
E side has shown wide sectors of the slope where
wedge failure has been detected, especially in the
lower parts of the slope where siltstone is prevalent,
although this kind of failure mode can mobilize small
volume of rocks due high frequency of discontinui-
ties. According to the main geomorphic processes
reconstructed in the Bamiyan cliff, a geomorphologi-
cal map has been produced (Figure 8).
Figure 7 : Results of kinematic analysis for wedge failure for W side (left) and E side of the cliff (middle); the arrows show the
intersections of planes that may cause sliding inside the potential area (crescent shaped region between slope limit and
lower friction cone). Potential wedge sliding along the cliff (right).
Figure 8 : View of the Bamiyan valley (upper) and geomorphological
map of the cliff where the giant statues of Buddha are located. The
distance between the niches is 790m. The lower aerial photo is the
fi rst image of the Bamiyan valley (late ’60)
Geomorphology and Landslide Potential
of the Bamiyan Valley, Afghanistan
SAARC Workshop on
Landslide Risk Management in South Asia
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The geomorphological investigation carried out in Bamiyan on the cliff where the giant statues of Bud-
dha are located has evidenced that several active processes are affecting the area. Intense erosion is
mainly affecting the upper part of the cliff and the slope face whereas landslide processes are involv-
ing different sectors of the slope. According to kinematic analysis undertaken in the structural stations
detected along the cliff of Bamiyan, the slope may experienced, as in the past, toppling, planar sliding
and wedge failure, although with distinct perspectives.
Planar sliding is the most diffuse failure potential both sides of the cliff, although most of the move-
ments have occurred in the past. This failure type can be considered as the secondary movement
type after toppling evolution of unstable blocks, especially when the failure surface is located inside
siltstone layers. Toppling of rock blocks is equally diffuse and may be considered the most hazardous
landslide type for all the cliff, even if in the W side it can be expected a higher magnitude of events
with respect to the E part of the cliff. Wedge sliding is potentially developing in both parts of the cliff.
Nevertheless, the structural conditions suggest that this type of movement is more probable in the
eastern sector, characterised by high potential frequency and low magnitude of events, as also sur-
veyed during the fi eld mission of June 2007.
Acknowledgments
The authors are sincerely grateful to UNESCO that funded the research. A special gratitude to the func-
tionaries of UNESCO Kabul for local support.
References
• Ambrasey N., Bilham R., 2003. Earthquakes in Afghanistan. Seismological Research Letters, 74, pp. 107-123.
• Bush, A.B.G., 2005. CO2/H2O and orbitally driven climate variability over central Asia through the Holocene.
Quaternary International, 136 (2005), pp. 15-23.
• Delmonaco, G., Margottini C., 2007. Geomorphological features of the Bamiyan valley. Report on the
UNESCO mission to Bamiyan (Afghanistan), 18-29 June 2007. UNESCO, Paris, 26 pp.
• Esper, J., Schweingruber, F.H. and Winiger, M., 2002. 1300 years of climatic history for Western Central Asia
inferred from tree-rings. The Holocene, 12 (3), pp. 267–277.
• Kamp, U.Jr. Haserod K. and F. Shroder,J.F. Jr., 2004. Quaternary landscape evolution in the eastern Hindu
Kush, Pakistan. Geomorphology, 57 (1-2), pp.1-27.
• Lang, H.D., 1971. Über das Jungtertiär und Quartär in Süd-Afghanistan. Beih. Geol. Jb., 96, Hannover, pp.
167-208.
• Lang, J., 1972. Bassins intramontagneux néogènes de l’Afghanistan Central. Rev. Geogr. Phys. Geol. Dynam.,
Paris, 1972 (2), 14, 4, pp. 415-427.
• Margottini C., 2001. Instability and geotechnical problems of the Buddha niches and surrounding cliff in
Bamiyan Valley, central Afghanistan. Landslides, Vol. 1, no. 1, Springer Berlin/Heidelberg, pp. 41-51.
• Reineke T., 2006. Environmental Assessment of the Bamiyan Valley in the Central Highlands of Afghani-
stan. In: University of Aachen, Bamiyan Masterplan Campaign 2005. Aachen.
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