Landslides (2017) 14:385–394DOI 10.1007/s10346-016-0756-9Received: 14 April 2016Accepted: 15 September 2016Published online: 27 September 2016© Springer-Verlag Berlin Heidelberg 2016

H. Deng I L. Z. Wu I R. Q. Huang I X. G. Guo I Q. He

Formation of the Siwanli ancient landslide in the DaduRiver, China

Abstract The Siwanli landslide is located in the middle section ofthe Dadu River in the eastern part of the Qinghai–Tibet Plateau ina complex regional geological environment. Strong erosion of theriver valley has caused numerous rockfalls and slides on both sidesof the valley since the Late Pleistocene. A large number of land-slide deposits provide the opportunity for examination of thesedimentary and erosional environment along the Dadu River.Identifying the spatial and temporal characteristics of the large,ancient landslides in the Dadu River valley can help improveunderstanding of the formation mechanism and evolutionary pro-cess of ancient and recurrent landslides. In this paper, the forma-tion mechanism of the ancient, complex, and multistage Siwanlilandslide is discussed, as well as an important link between rivererosion and the formation and evolution of the landslide. In thefirst stage, the initial landslide blocked the Dadu River, forming abarrier lake, and multistage landslide dam breaches occurred. Theentire landslide dam experienced creep deformation, and localminor multistage sliding occurred at the front and middle partsof the initial landslide. Subsequently, a large landslide formed atthe scarp of the initial landslide.

Keywords Dadu River . River erosion . Ancientlandslide . Multistage sliding . Siwanli landslide

IntroductionSouthwestern China extends across the eastern part of the Qing-hai–Tibet Plateau, and, as a result of the continuous uplift of theplateau, an orogenic mountain belt was formed along the N–Strending border between the Qinghai–Tibet Plateau and the Si-chuan Basin. During this uplift, rivers such as the Dadu Riverbecame deeply incised and formed steep valleys within the moun-tain belt. The strong interaction between these internal riverineforces and the external tectonic forces transformed the region,resulting in a complex and dynamic geomorphological environ-ment. The region is characterized by a high crustal stress environ-ment and active tectonics.

Complex geological and geomorphological environments, andchanges in global climate since the Quaternary, have caused large-scale slope instabilities, resulting in rock falls, slides, and debrisflows in the Dadu River valley (Table 1). In previous studies, largelandslides in the Dadu River were related to the effects of ancientearthquakes and climate change (Chai et al. 1995, 2000; Dai et al.2005; Zhao et al. 2014). However, it is also known that ancientriver-blocking events, such as the Diexi landslide, led to the for-mation of large barrier lakes and changes in the erosion andsedimentation processes of rivers. These ancient landslides alsoled to the formation of thick sedimentary deposits that cover thebedrock along the river valley.

A dammed barrier lake is formed when a slide, rock fall, ordebris flow completely blocks the river channel, which builds upinstability in the dammed river and landslide itself, both of whichbecome major geological hazards. Such dams and barrier lakes

have been extensively investigated for this reason (Keefer 1984,1994; Chai et al. 1995, 2000; Costa and Schuster 1988, 1991; Allenet al. 1991; Korup 2002; Dai et al. 2005; Weidinger 2006; Chen et al.2008; Korup and Montgomery 2008; Phartiyal et al. 2009; Evanset al. 2011; Zhang et al. 2011; Zhao et al. 2014).

The objective of this study is to investigate the formationmechanism and multistage sliding processes of the Siwanli land-slide. Field investigations were carried out to determine theboundaries of the landslide, the causes of the large size of theancient landslide, and the formation mechanism of multistagelandslides. The factors controlling the main and subsequent land-slides are analyzed, and it is considered that the results can beused to help identify and characterize ancient landslides that havedeveloped along river valleys.

Regional geological backgroundThe study site is located in the middle section of the Dadu River innorthwestern Sichuan Province, China, in the transition belt betweenthe Qinghai–Tibet and Yunnan–Guizhou Plateaus. As a result ofcollision with the Indo-Asian Plate in the Neogene, the study areaexperiences intensive tectonic activities, the development of activefaults, and frequent earthquakes. The major active faults in and nearthe area include the Daduhe, Xianshuihe, Anninghe, andLongmenshan faults (Fig. 1) (Allen et al. 1991). The active geologicalenvironment is also evident from the frequent occurrence of rock-falls, slides, and debris flows.

The study site is located in the upstream reaches of the DaduRiver in the eastern Qinghai–Tibet Plateau which is dominated by aplateau-like hummocky landform that occurs in the western part ofthe site. A geological map of the Siwanli landslide area, includinggeomorphology, borehole data, and rock structure, is shown in Fig. 2.

The mean annual temperature of the area is 16.2 °C, with amaximum of 39.2 °C and minimum of 5.0 °C. The annual averagerainfall from 1961 to 1990 in the middle part of the Dadu River valleyis 722.5 mm, with a maximum daily rainfall of 108.6 mm (Deng et al.2007). The slope gradient along both sides of the valleys is generallybetween 40° and 80°, and large amounts of scree accumulate at thefoot of the steep slopes. Many events caused by geological instabilityhave occurred in the middle part of the Dadu River (Dai et al. 2005)because the Dadu River flows through several different geologicalunits and the lithologies vary greatly and include basalt, slate, andsandstone rocks. The Kangding–Luding area is one of the mostseismically active regions of China (Wang and Pei 1987), and theseismicity is controlled primarily by the Xianshuihe active fault zone(Wang and Pei 1998).

Development of the initial landslide

Morphological characteristicsThe Siwanli landslide is located near the village of Siwanli inLuding County, between the upstream and downstream dam sitesof the Luding Power Station (Fig. 1). The landslide complex was

Landslides 14 & (2017) 385

Recent Landslides

identified as an ancient landslide based on its topographical fea-tures. The initial landslide has an armchair-like shape in whichmost of the material was displaced from the upper part anddeposited in the lower part (Figs. 3 and 4). The main slidingdirection was NW75°, and the west side of the accumulation areacontains three terrace-like steps that dip at NW55°, which devel-oped after the movement of the initial landslide.

The front of the landslide reached the Dadu River valley, andthe scarp developed into an ancient glacial terrace that is widelydistributed at high altitudes along the Dadu River. The residualalluvium and barrier lake sediments deposited by the damming ofthe river can be found upstream on the opposite bank of the mainriverbed. The initial landslide was 1400 m long and 800 m wide,with an elevation difference of about 500 m between the front edgeof the landslide and the scarp. The deposits of the initial landsliderange in elevation from 1280 to 1800 m above sea level (a.s.l.), andthere is a glacial terrace at 1800 m a.s.l. Drill cores show that themaximum thickness of the landslide body is 123 m, with a meanthickness of approximately 70 m. Thus, the initial landslide that

blocked the river flow had a volume of approximately5.280 × 107 m3 (Figs. 3 and 4). The present geomorphology, fol-lowing the initial landslide and other landslides, is shown in Fig. 4.

The landslide is located on the western concave bank of the DaduRiver where the river direction changes. The gully of the east flank(legend 9 on the eastern border of Fig. 3) caused by the initiallandslide has largely been infilled with colluvial deposits. A tensiletrough (in front of the largest rockfall in Fig. 3) was produced by asubsequent landslide near the ancient glacial terrace, and debrisfrom the landslide is distributed on both sides of this tensile trough.The debris particle size distribution is mostly in the 5–20-cm rangeand accounts for about 35 % of the total volume of the debris, theremaining mass consisting of blocky rocks. The gravel clasts consistof granodiorite with calcite veins. The east side of the initial landslideshows a morphological ridge and steep colluvial accumulation at thefoot of the scarp of the eastern boundary (Fig. 3).

At the scarp boundary, the cliff of the glacial terrace is dissectedby a fresh, crescent-shaped scarp formed by the sliding of thesubsequent landslide (Fig. 5). The residual glacial terrace is about

Table 1 Details of large ancient landslides between the towns of Hanyuan and Luding along the Dadu River valley

Name of ancientlandslide

Volume(×104 m3)

Scale Longitude andlatitude

Elevation of leadingedge (m)

Whetherdamming river

Date

Siwanli landslide 3500 Oversize N 29° 56′21″

1300 Yes 170thou-sand

E 102° 14′0″

Gangudi landslide 12,000 Oversize N 29° 48′43″

1380 Yes 220thou-sand

E 102° 13′2″

Chuni landslide 10,000 Oversize N 29° 48′41″

1380 Yes 220thou-sand

E 102° 12′20″

Jiajun landslide 8000 Oversize N 29° 40′2″

1280 Yes 190thou-sand

E 102° 12′4″

Moganglinglandslide

2500 Oversize N 29° 37′21″

1110 Yes In 1786

E 102° 9′40″

Lantianwanlandslide

5600 Oversize N 29° 35′34″

1160 Yes In 1786

E 101° 55′13″

Detuo landslide 430 Large N 29° 34′12″

1140 No 1200thou-sand

E 102° 1′59″

Xinhua landslide 950 Large N 29° 31′2″

1070 No –

Note: Large, 100–1000 × 104 m3 ; oversize, more than 1000 × 104 m3

Recent Landslides

Landslides 14 & (2017)386

550 m long and 150 m wide. The toe of the cliff is covered withrockfall deposits that form a steep slope with a gradient steeperthan 50°. A small rockfall with scree accumulation lies on the eastside of the glacial terrace (Fig. 6). At present, the riverbed in frontof the initial landslide lies at an altitude of about 1280 m. The frontdeposit of the initial landslide has a gradient steeper than 70° as aresult of highway excavation and undercutting by the river (Fig. 7).Gullies occur along the surface of the cliff, and some collapsedbecause of rainfall and erosional processes.

Material descriptionThe eastern part of the landslide lies on the western slope ofMount Erlang. Two branches of the Luding fault pass throughthe landslide in a northeasterly direction. The bedrock exposedin the landslide area is mainly granite, amphibolite, and phylliterocks of the Kangding Suite, with local exposures of diabase. Threegroups of structural planes are observed, with the following direc-tions: N25° E/NW75°, SN/W70°, and N65–75° W/SW63°. The thirdstructural plane is steep and strikes almost parallel to the slope;thus, local and superficial failure of the rocks in the region can bequite easily induced in this slope.

In the scarp of the landslide, two layers consisting ofancient till rubble deposits were identified. The particle sizeof these deposits is mainly in the 20–60-cm range, with localboulders >100 cm in size. The particles are poorly sorted and

poorly rounded, with a compacted structure. A Brochemoutonnée^ is visible and shows apparent glacial striations.The deposit at the front of the initial landslide consists main-ly of black mylonite and massive metamorphic gravel andsand that accounts for about 60 % of the rock fragments.The rock fragments at the front are angular, with a range ofsizes, and are chaotically arranged. They are composed ofphyllonite and amphibolites. Sand accounts for 30 % of thedeposit at the front of the landslide, and the sandy soil isweakly cemented.

Lake facies sediments, which were inundated because of reservoirfilling, are found in the Hunshui Gully on the opposite bank of theDadu River (Fig. 8). The sedimentary sequence can be sub-dividedinto four layers frombottom to top (Fig. 8), as described below. LayerI is alluvial gravel and sand about 0.4m thick. The pebbles aremostlydiorite, with minor amounts of granite. The gravel is sub-rounded torounded and cemented. Layer II (also alluvial deposits) is 0.2–0.3 mthick and consists of medium to coarse-grained sand with a layer ofgravel. The gravel is mainly 2–5 cm in size, moderately rounded,partially sorted, and weakly cemented. Layer III is 0.3–0.5 m thickand consists of horizontally bedded, gray silty laminated clay. Finegrit to coarse sand <2 cm in size is present between laminations andis partially cemented. Layer IV comprises colluvium that is 1.5–2.0 mthick and contains sub-angular and poorly sorted gravel clasts whichshow massive, well-consolidated bedding.

Anninghe fault

Xianshuihe fault

Luding Power Station

Fault

Fig. 1 Locality map and satellite image showing the Siwanli landslide along the Dadu River

Landslides 14 & (2017) 387

Formation mechanism and evolution of the initial landslideBased on our investigation and analysis of the basic char-acteristics of the Siwanli landslide, and in conjunction withinformation on the engineering geological environment, thebasic formation mechanism of this landslide can be de-duced. These deductions are discussed in the followingthree sub-sections.

Formation of loose depositsOn-site investigation and drilling indicate that bedrock is exposedat the boundaries of the landslide and on the opposite bank. Thesedeposits, about 80 m thick on average, were formed by the initiallandslide.

During glacier melting following the last glaciation, intensivefracturing caused the front slope to collapse, resulting in a land-slide. The landslide then became covered with large amounts ofgravelly soil deposits.

Preferred structural planesThree groups of preferred structural planes developed in thelandslide area and are consistent with the armchair-like topo-graphic shape. Two groups of steeply dipping structural planes(planes 2 and 3 in Fig. 9) formed a potentially continuous struc-tural plane in the slope, downslope of the ancient glacial gully(Fig. 3). Thus, an abundance of fissure water was present and,importantly, the structural planes are very steep, providing favor-able conditions for a landslide.

Geomorphological conditionsThe landslide area is located in a U-shaped section of the DaduRiver valley. The difference in elevation between the foot and thescarp crown is 500 m. The average slope gradient before thedevelopment of the initial landslide was >30°. At the scarp andon the east side of the landslide is a migration channel of anancient glacier, and on the west side is an ancient gully (Fig. 3).With the water level rising in the Dadu River during the last periodof deglaciation, the front of the landslide deposit in the concavebank was continuously eroded, and thus the front was continu-ously weakened.

Multistage minor slumping

Morphological characteristicsThree level terraces can be clearly observed at the east front part ofthe first landslide in a NW55° direction. From top to bottom, theelevations of the three terraces are 1479–1501, 1439–1453, and 1386–1453 m a.s.l, respectively. The three terraces are shown in Fig. 10.The large-scale first-level terrace was formed by a minor slump inthe middle section of the initial landslide, which led to the occur-rence of the subsequent large-scale landslide at the scarp (Fig. 3).The front of the third-level terrace has a gradient >70°. Loosesedimentary accumulations are found between the first-level andsecond-level terraces. Minor sliding further down the slope nearthe foot of the initial landslide was caused by long-term erosion ofthe Dadu River, creating the secondary and tertiary terraces.

f 2

f3

f4

f5

f6f7

f8

F2-1

F2-2

F2-2

F1

ZK01

ZK03

ZK01

Fig. 2 Geological map of the Siwanli landslide. 1 Alluvium; 2 deluvium; 3 colluvium; 4 proluvium; 5 landslide; 6 plagiogranite; 7 monzogranite; 8 amphibolite; 9 alteredamphibolite; 10 ductile shear belt; 11 fault; 12 geological boundary; 13 landslide boundary; 14 section line; 15 drill hole

Recent Landslides

Landslides 14 & (2017)388

Material compositionThe landslide deposit is mainly composed of rock and soil, inwhich the three terraces were formed by minor sliding (Figs. 9and 11). Large block-shaped rocks can be seen in the secondarylevel terrace, but are seldom found in the other terraces. Thedeposit is mainly composed of weakly weathered clasts of dioriteand granite that are angular to sub-angular. The particle size of therock fragments is generally 20–30 cm, while the gravel particles are<60 mm in size. Most of the material consists of coarse particlesthat form the framework of the matrix-supported deposit. Datafrom drill cores shows that there are no continuous weak planes inthe landslide and that the dip angle of the sliding surface rangesfrom 20° to 35°. The stratification at the foot of the landslide showsevidence of multistage sliding (at least three slides) that appears tobe caused by the erosion of the bank deposit formed by the DaduRiver.

Cause and mechanisms of the multistage minor slidingAfter the initial slide, two minor deep-seated slides occurred nearthe front of the deposit (Fig. 11). These slides may have beencaused by slope creep along the Dadu River valley and movedalong slip surfaces within the landslide deposit. Occurrence ofthese minor slides is related to changes in dynamic and staticwater pressure. The slow deformation was accompanied by ero-sion of the bank slope deposit which caused changes to the struc-ture of the deposit that reduced permeability at the front of thedeposit. The minor sliding affected the stability of the initiallandslide. The three level terraces, which are in line with theconcave bank of the Dadu River where strong erosion occurred,

were caused by minor slides, and the main sliding direction wastoward the north-northeast (20°).

Analysis indicates that the multistage sliding deformation inthe foot of the initial landslide has the following characteristics: (a)During the landslide blocking event, severe river erosion occurredin the foot of the landslide along the concave river bank. (b) Thesteep front (the original free surface) of the landslide createdenough space for the subsequent slides, and multistage slidingoccurred in a direction that deviated from the main sliding direc-tion (Fig. 3). (c) After the formation of the initial landslide, theDadu River continuously scoured and laterally eroded the foot ofthe landslide, particularly on the upstream side of the landslide.The water level of the Dadu River fluctuated rapidly because of thedamming of the river and dam collapse. In the latest event of dambreach, the water level of the Dadu River also changed significant-ly, corresponding to the period of post-glaciation. A series ofchanges in the base level of erosion in the foot of the landslidecaused changes in the water level of the initial landslide, togetherwith change in the erosion environment of the landslide foot part.Finally, multistage minor sliding deformations emerged at thefront of the landslide deposit.

The fractured structure of the landslide area and the de-posits from the first landslide are characterized by high po-rosity, low cohesion, and high permeability. The rising waterlevel of the Dadu River facilitated the formation of a high-water pressure field in the landslide accumulation area. Owingto increased pore water pressure, the resistance force of therock mass was weakened, ultimately resulting in formation ofthe minor landslides.

Fig. 3 Interpreted image of the Siwanli landslide based on a remote sensing image obtained in 2011. 1 Landslide boundary; 2 subsequent landslides in the scarp of theinitial landslide; 3 boundary of the initial landslide deposit; 4 boundaries of the multistage terraces; 5 rock fall; 6 tensile crack; 7 section lines; 8 migration channel of theancient glacier; 9 ancient gully; 10 mountain ridge

Landslides 14 & (2017) 389

Development of the subsequent large landslide

Morphological characteristicsFigure 3 shows the two subsequent landslides which developed inthe scarp of the glacial terrace, i.e., the first level terrace (seeFig. 10). The larger landslide is situated on the west side, and thesmaller one is on the east side. The deposits formed by laterlandslides, starting from the scarp of the ancient glacial terrace,overlie the first level terrace (Fig. 9). The largest subsequentlandslide (Fig. 9) has an armchair-like longitudinal profile that issteep on both sides and slopes gently in the middle. The gradientof the foot of the subsequent landslide slope is about 30°, and thelandslide comprises an elongated deposit that is relatively thick inthe foot. Deformations occurred at the eastern boundary thattoppled trees and resulted in exposure of tree roots that grew inthe initial landslide deposits. The subsequent slide is deep-seatedwith a sliding direction of NW80°, which is a slight deflectioncompared with the initial sliding direction. The length of thesubsequent landslide deposit on the west side is about 550 m,and the deposit is 250–450 m wide, 40 m thick, and has a totalvolume of 7.7 million m3.

Causes and mechanisms of the subsequent landslidesThe occurrences of subsequent landslide events are related topresent rock structure and are caused by earthquakes. The treeroots that grew in the initial landslide deposit disintegrated be-cause of these landslides and have become exposed by more recentsliding, indicating that the subsequent landslide deposits formedlong after the main landslide.

The scarp gradient of the initial landslide is steep, which accel-erated the disintegration of the ancient glacial terrace, and wasprobably triggered by seismic activity. Part of the glacial terracescarp was disintegrated into rock fragments, and, after the forma-tion of the initial landslide, a large number of colluvial depositsformed at the landslide scarp. The sliding, creep, and local multi-level sliding caused a steepening of the initial landslide scarp. The

sediment in the scarp of the landslide is poorly consolidated,enabling infiltration of surface water and flow of fissure water.Springs exposed on the eastern boundary of the subsequent land-slide provide strong evidence of this water infiltration.

As illustrated in Fig. 9, the deposit formed by the initial slidematerial is >80 m thick while the landslide material at the back ofthe first-level terrace is considerably thinner, thus the scarp willeasily fail as a result of shearing.

DiscussionAnalysis of the Siwanli landslide shows that it has multistagesliding characteristics. The sliding can be sub-divided into threestages: the deep-seated initial slide which reached downstream, thesubsequent landslide at the scarp, and the minor slumps thatformed the three existing terraces (Fig. 3). According to the slopedevelopment (Fig. 9), the multistage sliding process can be char-acterized as follows:

Fig. 4 Photograph showing the Siwanli landslide; view is upstream

Glacial terrace

Scarp

Fig. 5 The remnant of the ancient glacial terrace at the scarp of the landslide

Recent Landslides

Landslides 14 & (2017)390

1. The Siwanli landslide formed during the end of the Late Pleis-tocene (based on electron spin resonance analysis of samplesfrom the bottom layer in front of the landslide). The landslidestarted at the U-shaped edge of the glacial terrace and hasexperienced large climatic changes during the last glacial peri-od and suffered erosion from the Dadu River and resultingwater level fluctuations.

2. There are retrogressive effects in the foot of the initial slide, giventhat the landslide deposit is located on the concave riverbankand has been seriously eroded by the Dadu River, particularly onits upstream front edge. The Dadu River continually eroded andscoured the slope toe, and creep deformation was produced inthe deposit in addition to the dynamic water pressure actionwithin the deposit caused by water level fluctuations of the DaduRiver. The landslide dammed the river but then failed, leading tothe formation of a large-scale first-level terrace at the back of theinitial landslide mass and new minor sliding that formed thesecondary and tertiary terraces.

Fig. 6 Rockfall on the east side of the glacial terrace that is also shown in Fig. 3

Fig. 7 Initial landslide deposit exposed in front of the Dadu River valley and highway

Layer IV

Layer III

Layer II

Layer I

Fig. 8 Lacustrine layer (III) intercalated between fluvial deposits on the river bankopposite of the landslide

Landslides 14 & (2017) 391

3. A loading effect caused by the head scarp of the initialslide and accumulation of colluvial deposits, as well asminor sliding, occurred at the steep headscarp of theinitial landslide. Deposits from collapsed rock accumula-tions were continuously accumulated on the ancient glacialterrace (Fig. 3), forming a large amount of loose deposits.Meanwhile, after the subsequent landslide, large amounts

of debris covered the first-level terrace, causing furthershifting of the load distribution in the initial landslidedeposit.

The multistage sliding of the Siwanli landslide occurred ina complex geological environment that has been subjected to

Road

DaduRiver

54.2

100 2000

149254.2 49.0

ZK03

144173.3 81.9

ZK02

1394101.192.2ZK01

1394101.1 92.2ZK01

N75° W18201800178017601740172017001680166016401620160015801560154015201500148014601440142014001380136013401320130012801260

Distance 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 1250 1300 135012601280130013201340136013801400142014401460148015001520154015601580160016201640166016801700172017401760178018001820

(m) (m)

Legend

First level platform

Second level platform

Third level platform

1

3

5

7

9

2

4

6

8

10

Fig. 9 Vertical section (I–I′ in Fig. 3) through the Siwanli landslide. 1 Colluvial gravelly soil; 2 sliding surface of the initial landslide; 3 gravelly soil of the initial landslide; 4sliding surface of the subsequent landslide at the scarp of the initial landslide; 5 migmatitic granite; 6 Dadu River; 7 gravel and boulders; 8 exploration drill holes; 9 initialtrailing edge line of the initial sliding surface; 10 depth of drill hole

Fig. 10 Three level terraces on the east side of the front of the Siwanli landslide

Recent Landslides

Landslides 14 & (2017)392

tectonic activity, climate change, and variations in the ero-sional and depositional processes of the Dadu River. Erosionof the river valley in the foot of the landslide induced land-slide movement and multistage sliding, which mostly occurredin the foot of the slopes along the Dadu River. The movementof the initial landslide provided space for consequent land-slides at the scarp. Some of the deposits of the subsequentlandslides accumulated on the first-level terrace (Fig. 9),greatly affecting the stability of the overall landslide body.

Data from the 2008 Wenchuan earthquake were used toverify that the area where the landslide is located is on thehanging wall of a thrust fault (Huang and Xu, 2008). Sucha slope would be easily disturbed by a strong earthquake,resulting in rapid slope failure with a large run-out into theriver, as well as barrier dam formation. Thus, the initiallandslide at the study site, which was a rockslide, may havebeen triggered by an earthquake, and the active tectonicprocesses and structural conditioning likely played keyroles in controlling the evolution of the landslide.

ConclusionsBased on our field investigation and analysis of the Siwanli ancientlandslide, the following conclusions can be drawn:

1. The Siwanli ancient landslide experienced the followingstages of evolution: an initial slide blocked the DaduRiver; a barrier lake was formed; the dam then failed;and the landslide experienced creep deformation, and ero-sion in the foot of the landslide body led to local multi-stage landslides in the foot of the landslide and asubsequent landslide from the initial landslide scarp.

2. The formation and evolution of the Siwanli ancient land-slide are closely related to climate change and frequentchanges in the erosional and sedimentation processes ofthe valley. Valley incision, river erosion, landslide dambreach, and a steep morphology in the foot of the land-slide body induced multistage minor landslides. Two mi-nor slides contributed to the creation of the existingthree terraces.

AcknowledgmentsWe thank constructive suggestions from Dr. van Asch TWJ.We thank the National Basic Research Program of China (973Program) (No. 2013CB733202), investigation and evaluation ofslope geological disasters in the thick valleys of SouthwestChina (No. 12120113010500), and the National Natural ScienceFoundation of China (Nos. 41272332 and 41672282). The sec-ond author thanks the Innovative Team of the Chengdu Uni-versity of Technology.

References

Allen CR, Luo Z, Qian H, Wen X, Zhou H, Huang W (1991) Field study of a highly activefault zone: the Xianshuihe fault of southwestern China. Geol Soc Am Bull 103:1178–1199

Chai HJ, Liu HC, Zhang ZY (1995) The catalog of Chinese landslide dam events. Journal ofGeological Hazards and Environment Preservation 6(4):1–9 in Chinese

Chai HJ, Liu HC, Zhang ZY, ZW X (2000) The distribution, causes and effects of damminglandslides in China. Journal of Chengdu Institute of Technology 27:302–307 inChinese

Chen J, Dai FC, Yao X (2008) Holocene debris-flow deposits and their implications onclimate in the upper Jinsha River valley, China. Geomorphology 93:493–500

Costa JE, Schuster RL (1988) The formation and failure of natural dams. Geol Soc Am Bull100:1054–1068

Costa JE, Schuster RL (1991) Documented historical landslide dams from around theworld. US Geological Survey Open-File Report 91-239:486

Dai FC, Lee CF, Deng JH, Tham LG (2005) The 1786 earthquake triggered landslide damand subsequent dam-break flood on the Dadu River, southwestern China. Geomor-phology 65:205–221

Deng JH, Chen F, Yin H, Gao MZ, Meng YL, Huang RT (2007) Geological origin andstability evaluation of the Siwancun landslide in Luding County. Chin J Rock Mech Eng26(10):1945–1950

Evans SG, Hermanns R, Strom A., Scarascia-Mugnozza G (Eds) (2011) Natural and artificialrock slide dams. Springer (Series: Lecture Notes in Earth Sciences).

Huang RQ, Xu Q (2008) Catastrophic landslide in China. Science Publishing House,Beijing, China (in Chinese).

Keefer DK (1984) Landslides caused by earthquakes. Geol Soc Am Bull 95:406–421Keefer DK (1994) The importance of earthquake-induced landslides to long-term slope

erosion and slope-failure hazards in seismically active regions. Geomorphology10:265–284

Korup O (2002) Recent research on landslide dams—a literature review with specialattention to New Zealand. Prog Phys Geogr 26:206–235

DaduRiver

RoadThird level platform

Second level platformFirst level platform

1000 501520

1500

1480

1460

1440

1420

1400

1380

1360

1340

1320

1300

1280

Distance 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 8501260

1280

1300

1320

1340

1360

1380

1400

1420

1440

1460

1480

1500

1520(m) (m)

N55° W

1

3

5

2

4

61283

1283

Fig. 11 Vertical section through the Siwanli landslide from II to II′ in Fig. 3. 1 Gravelly soil from the landslide; 2 first-period minor sliding surface; 3 migmatitic granite; 4second-period minor sliding surface; 5 gravel and boulder; 6 Dadu River

Landslides 14 & (2017) 393

Korup O, Montgomery DR (2008) Tibetan plateau river incision inhibited by glacialstabilization of the Tsangpo gorge. Nature 455:786–789

Phartiyal B, Sharma A, Srivastava P (2009) Chronology of relict lake deposits in the SpitiRiver, NW Trans Himalaya: implications to Late Pleistocenee Holocene climate-tectonic perturbations. Geomorphology 108:264–272

Wang XM, Pei XY (1987) The 1786 Kangding-Luding earthquake. Earthquake Research inSichuan 1–51. (Supplement Issue, in Chinese).

Wang XM, Pei XY (1998) Major active faults and earthquake-induced cracks inKangding-Luding area. Earthquake Research in Sichuan 1-2:46–56 inChinese

Weidinger JT (2006) Landslide dams in the high mountains of India, Nepal and China -stability and life span of their dammed lakes. Italian Journal of Engineering Geologyand Environment 1:67–80 special issue

Zhang YS, Zhao XT, Lan HX, Xiong TY (2011) A Pleistocene landslide-dammed lake,Jinsha River, Yunnan, China. Quat Int 233(1):72–80

Zhao Y, Xu M, Guo J, Zhang Q, Zhao HM, Kang XB, Xia Q (2014) Accumulationcharacteristics, mechanism, and identification of an ancient translational landslidein China. Landslides:1–12

H. Deng : L. Z. Wu ()) : R. Q. Huang : X. G. Guo : Q. HeState Key Laboratory of Geohazard Prevention and Geoenvironment Protection,Chengdu University of Technology,Chengdu, Sichuan 610059, People’s Republic of Chinae-mail: cewulz@gmail.com

Recent Landslides

Landslides 14 & (2017)394