Landslide Reactivation Research Articles

Structure from Motion Multisource Application for Landslide Characterization and Monitoring: The Champlas du Col Case Study, Sestriere, North-Western Italy.

Structure from Motion (SfM) is a powerful tool to provide 3D point clouds from a sequence of images taken from different remote sensing technologies. The use of this approach for processing images captured from both Remotely Piloted Aerial Vehicles (RPAS), historical aerial photograms, and smartphones, constitutes a valuable solution for the identification and characterization of active landslides. We applied SfM to process all the acquired and available images for the study of the Champlas du Col landslide, a complex slope instability reactivated in spring 2018 in the Piemonte Region (north-western Italy). This last reactivation of the slide, principally due to snow melting at the end of the winter season, interrupted the main road used to reach Sestriere, one of the most famous ski resorts in north-western Italy. We tested how SfM can be applied to process high-resolution multisource datasets by processing: (i) historical aerial photograms collected from five diverse regional flights, (ii) RGB and multi-spectral images acquired by two RPAS, taken in different moments, and (iii) terrestrial sequences of the most representative kinematic elements due to the evolution of the landslide. In addition, we obtained an overall framework of the historical development of the area of interest, and distinguished several generations of landslides. Moreover, an in-depth geomorphological characterization of the Champlas du Col landslide reactivation was done, by testing a cost-effective and rapid methodology based on SfM principles, which is easily repeatable to characterize and investigate active landslides.

Estimativa de Velocidade de Onda de Cisalhamento pela Inversão Conjunta de Curvas HVSR e f-k sob a Hipótese do Campo Difuso: um Estudo de Caso do Deslizamento de Sobradinho

Brazilian landslides are characterized as shallow, clay rich and are commonly triggered by the summer rainfalls. Therefore, the landslide geological information, such as shear surface location, has a paramount importance in their mechanism comprehension. The most adapted methods for the estimation of shear wave velocity profile are borehole stratigraphic logs or Standard Penetration Test (SPT) and Cone Penetration Test (CPT). However, the present study applied shear wave velocity estimation of Sobradinho landslide (SLS) by a joint inversion of horizontal to vertical spectral ratio (HVSR) curve and dispersion curve (DC) extracted from frequency-wavenumber (f-k) analysis of ambient noise records. HVSR curves at all the stations in the area exhibit the ubiquitous resonance frequency peak at 2 Hz indicates that at these stations the substratum is common. The f-k results for E-W component let us obtain an acceptable DC between 5 and 7 Hz range. Finally, joint inversion was interpreted based on the diffuse field assumption. The initial model was proposed to be a three-layered over a half-space. Results of joint inversion indicate that the substratum is at 24 m depth, with Vs values close to 1500 m/s. DC defines two layers overlaying the substratum: superficial layer with velocities near to 200 m/s (7m thick), and the second layer with Vs value of 1000 m/s. We think that abrupt rheology (stiffness) change between the first and the second layer could provide an evidence of the landslide re-activation during moderate to strong rainfall events. The proposed methodology will prove a reconnaissance survey for the detailed geotechnical investigations that will confirm the obtained results.

Reactivation of a huge ancient landslide by surface water infiltration

An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method (FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7–9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.

Modeling of subcritical cracking in acidized carbonate rocks via coupled chemo-elasticity

Injection of acidized water into the crack process area has been known for long to induce subcritical crack propagation. Acid rain or vegetation decomposition can cause activation or reactivation of landslides at subcritical stress, while acid injection is used to enhance oil and gas reservoir stimulation. Equally promising is acid enhancement of crack propagation in geothermal field stimulation. To quantify the above mentioned processes, crack propagation is simulated using a chemo-elasticity model in which a chemically controlled strain is added to linear elastic strain, in analogy to thermal strain. That strain is proportional to accumulated mass removal, controlled by a chemical reaction. The coefficient of chemical shrinkage is either constant, or is postulated to depend on the level of straining of rock using various scalar measures of either volumetric or shear strain to simulate the dependence of mineral dissolution on micro-cracking. With that formulation an Airy stress function, as in classical linear elasticity solution, has been for the first time, to our knowledge, used for solving chemo-elasticity problem, by employing an additional particular potential term. The results suggest that a constant chemically induced shrinkage alone is not sufficient to produce any significant enhancement of the crack tip displacement. However, making the coefficient of chemical shrinkage dependent on a shear strain invariant (and hence making the constitutive law implicit), leads to an enhancement of crack propagation velocity at a desired level. Yet, the obtained crack propagation acceleration appears to be too modest. That suggests that to obtain realistic results, in addition to diffusive transport, the advective–reactive transport process (especially, permeability) should be as well coupled to deformation.

Differences between the responses of European larch (Larix decidua Mill.) and Norway spruce (Picea abies (L.) Karst) to landslide activity based on dendrogeomorphic and dendrometric data

Investigations of mass movement hazards need to be supported by accurate data regarding past frequencies of landslide reactivations. Dating landslide events using tree rings is a reliable approach for vegetated slopes in temperate climates. Despite the enhanced use of dendrogeomorphic research during recent decades, little is known about the specific responses of Larix spp. to landslide movements. We investigated the active section (~0.6 ha) of a complex landslide in the Vsetínské vrchy Mts. (Outer Western Carpathians) that is overgrown by a forest stand composed of European larch (Larix decidua Mill.) and Norway spruce (Picea abies (L.) Karst.). Using the dendrometric and dendrogeomorphic data identified from 74 trees (33 L. decidua and 41 P. abies), including the number and types of growth disturbances (GDs) and compiled event chronologies, we compared the responses of both tree species to the same landslide reactivations.We observed the same mean tree stem inclination for both tree species, whereas the inclination azimuths differed. L. decidua generally showed a higher number of stem bends compared to P. abies. Similar proportions of subjectively identified GDs (compression wood, CW, and abrupt growth suppression, GS) and mathematically identified GDs (tree-ring eccentricities) were observed in both tree species. However, the total number of GD.tree−1 was slightly higher in L. decidua (4.1) than in P. abies (3.2). A higher abundance of GS was identified in L. decidua at the expense of CW compared to P. abies. The event chronology based on the mathematical approach revealed slightly more landslide signals than for the subjective approach, mainly in L. decidua. However, the largest known landslide reactivation (in 1997) was recorded in all cases in both tree species. Based on the CW analysis, it was shown that larger stem inclinations are associated with longer persistence of CW in P. abies (rather than L. decidua), resulting in the possible masking of younger landslide events. By contrast, P. abies compensates for that limitation by having a generally shorter mean duration of CW than L. decidua. Overall, it seems that the complexity of landslide movements and root system architecture influenced the number and character of GDs in both tree species. In addition, we did not find any relationships between the measured dendrometric parameters and number of GDs to better assess the most suitable trees for dendrogeomorphic dating prior to sampling. Therefore, we recommend sampling both tree species when they overgrow the same landslide body so that the final event chronology will be more robust and possible limitations of one tree species can be eliminated by the benefits of the second.

Effect of locally accumulated crushed stone soil on the infiltration of intense rainfall: a case study on the reactivation of an old deep landslide deposit

An old landslide deposit situated in Deqin County, Yunnan Province, China, was used to investigate the effects of local accumulation of crushed stone soil on infiltration of intense rainfall. This study considers the infiltration process and landslide stability using finite-element method (FEM)-based models and a physical experimental model. The results show that reactivation of the old landslide was triggered by intense rainfall that occurred on 7–9 October 2012. The crushed stone soil played a key role in the rapid infiltration of rainfall deep into the landslide deposit. Accumulated rainfall and runoff water caused the formation of high pore water pressure in the crushed stone soil, which induced higher infiltration of the surrounding soil due to the higher gradient. The original slip zone was another key factor, as infiltrated water accumulated at the slip zone and form a high pore water pressure due to the lower permeability of the slip zone. The high pore water pressure that formed at the slip zone was the main factor triggering reactivation of the landslide during the rainfall.

Characteristics and mechanisms of coupled road and rainfall-induced landslide in Sichuan China

Field reconnaissance, geological mapping and photographic interpretation are utilized to study the failure mechanisms of July 2 catastrophic debris slide in 2017. The results suggested that the landslide was a reactivation of an ancient landslide after periods of relative dormancy, as manifestation of a retrogressive motion, which is triggered by the continuous engineering excavation as leads to rock mass unloading and decrease of mechanical properties of rock–soil mixture. The reactivated zone dominantly spread on the upper part of the ancient landslide area. The frequent tectonic movements rendered the potential landslide zone by fragmenting the structure. The fractured and fissile rock mass became further weakened by incessant rainfall that finally led to the failure of the rock mass.

La sequenza sismica dell'Italia centrale del 24 agosto e successive: contributi alla conoscenza e la banca dati degli effetti di superficie

The effect of earthquakes on structures and landscape can basically be divided into two types: direct and secondary effects. The direct effects are related to the deformation of the ground at the fault whose breakage has generated the seismic event and the effects are limited to an area that is short and close to breakage. The secondary effects resulting from the temporary passage of seismic waves may, however, also affect very large areas, causing a widespread presence of permanent effects on the Earth’s surface which may affect very large areas, which, in relation to the length of the fault and the magnitude released by the event can be in the order of thousands of km2. Following the seismic events commenced on 24 August 2016 (M6.0) and continued with the shocks of October 26 (M5.4 and M5.9) until October 30 (M6.5), the Unicam GeomorphoLAB Group has mapped and computerized about4000 permanent deformations on the Earth’s surface recognized in an area of over 6000 km2: fractures to the ground, activation and reactivation of large landslides and DGPV, dolines, mud volcanoes and liquefaction phenomena, landslides and small dams, changes in the water regime of the springs and the flow of rivers, cracks and /or fractures and / or deformations on network infrastructures, etc. The present work, therefore, based on the database and the GIS on surface effects, aims at representing a cognitive and interpretative contribution to the surface evidence produced during the seismic crisis of central Italy, looking, based on correlations with the seismic events that affected Umbria-Marche in 1997 and L’Aquila in 2009, to verify and implement, if necessary, the ESI scale which, in the specific case, seems to underestimate its effects. The analysis allowed to verify a high number of surface effects related to fracturing and seismic cracking and deformations on road and network infrastructures and, instead, a low number of activations and / or reactivations of landslides or subsidence. Although small, very significant is the number of variations of the water regime of the springs.

Analysis of deformation mechanism of landslide in complex geological conditions

This paper describes an interesting landslide located in the mountainous area of Zhejiang Province, China, which was caused by highway construction. Due to the complex geological conditions, the failure mechanism of the landslide is particularly difficult to analyze. The soil deformations were initially judged to be shallow and partial sliding. However, engineering measures used to stabilize the sliding masses failed. By establishing a comprehensive monitoring system composed of GPS, inclinometers and groundwater level monitors, the deformation of landslide was monitored. It is found that the previous deformation mechanism assumed without the monitoring data is incorrect. On the other hand, there is a large rock ancient landslide in the site, and deformation of the soil mass was caused by the reactivation of this ancient landslide. This case study illustrates the importance to deeply analyze the geological data and the field monitoring data and to correctly understand the geological conditions.

Landslide deformation behavior influenced by water level fluctuations of the Three Gorges Reservoir (China)

Water level fluctuations that occurs during filling-drawdown operations in man-made reservoirs can result in accelerations or reactivations (or even catastrophic failure) of large landslides. For disaster mitigation, a monitoring system comprising manual and automatic GPS systems, borehole inclinometers, and groundwater piezometers was installed to investigate the slope deformation behavior of a large reactivated landslide known as the Shuping landslide at the Three Gorges Reservoir, China. The long-term monitoring data (2003–2015) focused on the landslide deformation, which was triggered by water level fluctuations, is presented in this study. The cumulative displacement curves showed a step-like behavior, suggesting a lower base activity superimposed by phases of acceleration, which appeared during reservoir drawdown periods and rainy seasons. Based on statistical Pearson correlation analysis, the increase in landslide activity is dominated by reservoir water drawdown, rather than rainfall. The durations of the slide acceleration phases are much shorter than the reservoir water drawdown durations. Based on in-site piezometer monitoring data and numerical simulation, the potential causes are the hydraulic processes in the slope with much smaller groundwater drawdown velocities and hydraulic gradients in the initial stage of the reservoir water drawdown period.

Characterizing the spatial distribution and fundamental controls of landslides in the three gorges reservoir area, China

A comprehensive field investigation and analysis of the spatial distribution of landslides was conducted in the Three Gorges Reservoir Area (TGRA) along the Yangtze River and its first-order tributaries. A landslide inventory for this area was prepared using regional-local geological investigations and other available information. The analysis of the extensive inventory data reveals that the occurrence of landslides is mainly affected by four primary factors: (1) Lithology—the highest incidence of landslides is associated with the lithological combination of marl and shale intercalated with mudstone (MSM), and a number of landslides occurred in an area dominated by sandstone and mudstone intercalated with shale and coal seams (SMSC), which cover a major part (approximately 71%) of the bank slopes; (2) Structure—slope structure fundamentally controls the development of the sliding zone and the mechanism of formation of landslides occurring on the same lithological combinations at subregional scales. Landslide concentrations in consequent slopes are approximately 5–17 times greater than those of reverse slopes and diagonal slopes; (3) Topography—landslides are particularly abundant between elevations of 100 m and 600 m. The elevations of the headscarps of the landslides gradually decrease from the head to the tail of the reservoir due to the topography, and almost all of the toes of the landslides are below the highest historical floodwater level. The analysis of the correlation between landslide occurrence and hillslope gradients shows that 50% of all landslides occurred on slopes between 10° and 15°, despite slopes in this range representing only 30% of the total hillslope gradients; and (4) Water level fluctuation and precipitation—the fluctuation of reservoir water level exerts a fundamental effect that controls the occurrence and reactivation of landslides during the period of initial impoundment, whereas the precipitation becomes even more important than water level fluctuation after the first impoundment at 175 m above sea level. In addition, the comprehensive analysis performed in this study provides broad insight into the landslide distribution in the TGRA. This work will improve our understanding of the role of morphological and geological conditions that affect the occurrence of landslides, which may provide useful guidance for regional risk assessment and landslide susceptibility studies.

Comparison of single- and dual-permeability models in simulating the unsaturated hydro-mechanical behavior in a rainfall-triggered landslide

Landslide-prone slopes in earthquake-affected areas commonly feature heterogeneity and high permeability due to the presence of cracks and fissures that were caused by ground shaking. Landslide reactivation in heterogeneous slope may be affected by preferential flow that was commonly occurred under heavy rainfall. Current hydro-mechanical models that are based on a single-permeability model consider soil as a homogeneous continuum, which, however, cannot explicitly represent the hydraulic properties of heterogeneous soil. The present study adopted a dual-permeability model, using two Darcy-Richards equations to simulate the infiltration processes in both matrix and preferential flow domains. The hydrological results were integrated with an infinite slope stability approach, attempting to investigate the hydro-mechanical behavior. A coarse-textured unstable slope in an earthquake-affected area was chosen for conducting artificial rainfall experiment, and in the experiment slope, failure was triggered several times under heavy rainfall. The simulated hydro-mechanical results of both single- and dual-permeability model were compared with the measurements, including soil moisture content, pore water pressure, and slope stability conditions. Under high-intensity rainfall, the measured soil moisture and pore water pressure at 1-m depth showed faster hydrological response than its simulations, which can be regarded as a typical evidence of preferential flow. We found the dual-permeability model substantially improved the quantification of hydro-mechanical processes. Such improvement could assist in obtaining more reliable landslide-triggering predication. In the light of the implementation of a dual-permeability model for slope stability analysis, a more flexible and robust early warning system for shallow landslides hazard in coarse-textured slopes could be provided.

Complex rock slope deformation at Laxiwa Hydropower Station, China: background, characterization, and mechanism

An unstable rock slope called the Guobu landslide, observed in granite with a maximum cumulative displacement of 45 m, located on the upper stream of the dam of the Laxiwa Hydropower Station, China, and directly threatening the safety of the dam and the people living downstream, was investigated. Detailed field surveys, geological structure investigations, remote sensing image analysis, and GPS displacement monitoring were carried out to investigate the deformation characteristics of the slope after reservoir impoundment, historical deformation, ancient landslide reactivation, the influence factors of the large deformation of the slope, and the mechanism. Based on the results of the above analyses, it was seen that there is a clear geological structural dependence of the failure mechanisms in the study area, and that the complex failure mechanisms include toppling, subsiding wedge failure, rockfalls, and tension cracking in deep-seated rock masses. Moreover, analysis of the remote sensing images indicated that the ancient landslide had been reactivated between 2005 and 2008. Detailed field displacement monitoring data showed that the whole slope was deforming significantly and continuously with the increase of the water level in the reservoir. The displacement rate had a positive correlation with the variation of the reservoir water level, increasing and decreasing as the the latter rose and fell, respectively. The vulnerable geological conditions, water infiltration, and the reservoir impoundment were the main factors causing the large deformation of the Guobu landslide. Water infiltration was the driving force resulting in the reactivation of the ancient landslide, and the reservoir impoundment accelerated the slope deformation. The mechanism of the large deformation of the rock slope was a combination of the upper pushing deformation induced by wedging and toppling, due to the ancient landslide reactivation, and the lower traction deformation due to the reservoir impoundment.

Research Progress and Prospect on Reactivation of Ancient Landslides

Research Progress and Prospect on Reactivation of Ancient Landslides

Regional, tree-ring based chronology of landslides in the Outer Western Carpathians

Landslides are a type of mass wasting and denote any downslope movement of soil and rock under the influence of gravity; as such they can represent a dangerous natural hazard process, especially in case that they affect inhabited areas or transport infrastructure. Because the occurrence of landslides is typically favoured by terrain and lithological conditions, the process is frequently concentrated in relatively small, isolated regions exhibiting suitable initial conditions of terrain instability. Extensive regional assessments of landslide activity have been used in the past to uncover common triggers and process patterns, mostly in the aftermath of large, regional disasters. By contrast, however, regional reconstructions of past landslide activity have not been realized with dendrogeomorphic techniques, and with the aim to date past landslide histories over extended time periods and with annual dating precision. This study therefore aims at disentangling landslide dynamics at the regional scale (covering ca. 600 km2) by using growth-ring records of trees that grow on active landslides. The studied area of the Hostýnsko-vsetínská hornatina Mts. (Central Europe) is well known for its high landslide activity, but has so far been lacking a detailed chronology of past events. To this end, we dated past activity on 26 landslide bodies using tree-ring series from 1322 disturbed trees to reconstruct 327 landslide reactivations during the last century.The reconstructed landslide database allowed correlations between landslide types and their frequencies or occurrence, as well as inferences between selected morphometric parameters with landslide frequency and magnitude. We also observe periods of increased landslide activity (1940s, 1960s, 1980s, and 1990s) and events of regional importance (e.g., 1961, 1985, and 1997), as well as a significant decrease in landsliding during the last two decades.

Reactivation characteristics and dynamic hazard prediction of an ancient landslide in the east margin of Tibetan Plateau

The increasing human engineering activities and frequent extreme weather events have caused extensive reactivation of ancient landslides, which are widely developed in the east margin of Tibetan Plateau. The Shangyaogou landslide, as a typical ancient landslide example in this area, was investigated to reveal the reactivation characteristics, and its stability was calculated under the continuous rainfall condition with the intensity 30 mm/day using the finite element software Geo-Studio. The whole movement process and hazard prediction under the different triggering conditions were simulated using the numerical software DAN3D. The study results showed that: (1) under the joint influence of Mw 7.9 Wenchuan earthquake, toe erosion and intensive rainfall, multi-stage deformations occurred to the front part of the Shangyaogou landslide in multiple periods and also indicated a significant potential instability; (2) under the continuous rainfall condition, when the single effective total infiltration reached about 65 mm, the reactivation part will become unstable. While the single effective total infiltration reached about 120 mm, both reactivation part and posterior part became instability; (3) the maximum run-out distance of the reactivation part was calculated to be 350 m, and the forefront of the accumulation deposit would not reach the residential area; When both parts failed simultaneously, the maximum run-out distance was calculated to be 550 m by considering the thickness and dynamic energy of the accumulation deposits, and the vulnerable elements inside the fan area with radius of 150 m would be severely threatened; (4) abundant earthquake-triggered landslides have been developing in history or in recent years in the eastern margin of Tibetan Plateau. Some of them have been partly reactivated due to the increasing human engineering activities and extreme rainfall events, and they have a potential for further deformation and failure. The presented study methods can provide guidance for local disaster prevention and mitigation, and can be used as a reference for the hazard prediction of the similar ancient landslides which have been reactivated.

Slope dynamics and streambed uplift during the Pergalla landslide reactivation in March 2016 and discussion of concurrent causes (Northern Apennines, Italy)

On March 28, 2016, the toe zone of the apparently dormant Pergalla earthslide-earthflow (Northern Apennines, Italy) had a paroxysmal reactivation. In the course of 2 days, displacements up to almost 8 m severely damaged several houses and roads. At the bottom of the slope, the emersion of rotational sliding surfaces determined the uplift of almost 3 m of the Nure river streambed that was consequently partially dammed. The paper describes the landslide event on the basis of field surveys and analysis of post-event aerial photos, as well as data from geophysical surveys and pre- to post-failure displacement monitoring. It also discusses the possible concurrent causes of the event, including antecedent rainfall, the migration of active streambed channels of Nure river toward the landslide toe in the previous year, and the existence of long-term pre-failure slow movements. It is concluded that these factors, together with the presence of sliding surfaces extending beneath the valley floor, should be primarily considered if a preventive assessment of river damming potential due to streambed uplift should be made for other similar landslides in the Apennines.

Co-seismic surface rupture of Papatea fault and reactivation mechanism of the Clarence landslide during the 2016 Mw7.8 Kaikoura earthquake, New Zealand

Large earthquake-triggered landslides near a seismogenic fault are usually closely linked to fault slipping. Therefore, it is important to research the relationship between the landslide movement and the deformation pattern of faults to better understand the location and influencing factors related to the large landslides. A large landslide, on the right bank of the Clarence River, New Zealand, was reactivated during the 2016 Mw 7.8 Kaikoura earthquake. The landslide is located in close proximity to the Papatea Fault which ruptured during the earthquake. The special tectonic location of this landslide provided favorable conditions to research the failure mechanism of earthquake-triggered landslides. Field investigation and remote-sensing images revealed that the co-seismic surface rupture zone of the Papatea Fault is relatively complicated and characterized by a wide deformation zone with a width of ~80–170 m. The northern section showed as left-lateral strike-slip and thrust-slip, with a vertical displacement of up to 4–6 m. However, it exhibited thrust motion in the Clarence landslide area. The Clarence landslide was a reactivation of a pre-existing landslide. The thrust faulting of the Papatea Fault produced a wide deformation and fractured zone near the top of the landslide mass, and resulted in over-steepened topography in the landslide area. It should be noted that long-team seismic shaking, especially the main frequency of the seismic acceleration and rapid co-seismic vertical slip of the fault, played the principal role in further accelerating topographic instability during the earthquake. The landslide body thus started to slide along a pre-existing sliding surface under these actions. Our results indicate that the deformation pattern of the seismogenic fault could also play an important role in the occurrence of earthquake-triggered landslides, in addition to geological and geomorphological conditions and local seismic acceleration.

Analyzing successive landslide dam formation by different triggering mechanisms: The case of the Tangjiawan landslide, Sichuan, China

The catastrophic Tangjiawan landslide, triggered by the 2008 Wenchuan earthquake, blocked the Duba River, impounding one of the most dangerous coseismic barrier lakes in Beichuan, China. The lake was drained by an artificial spillway within one month after the earthquake to minimize the potential dam-breach flooding risk. However, on September 5, 2016, this landslide was reactivated and dammed the river again, creating a 20-m high dam at the same location and resulting in the formation of a barrier lake with a volume of 0.6 million m3. The day after the event we carried out a field investigation of the landslide and obtained a high-resolution image and DEM using UAV. The satellite images from 2005, 2008, 2010 and 2015 were also collected to analyze the evolution of the landslide. Together with multi-temporal DEMs, the geometry and volumes of the displaced mass and the landslide dams and barrier lakes were calculated using image interpretation and 3D spatial analysis with GIS. This landslide is of great scientific interest, as it presents a good example of multiple reactivation of a pre-historical giant landslide under different triggering conditions: a reactivation of an older landslide during the Wenchuan earthquake, and a second reactivation during a rainfall event several years later. Meanwhile from the hazard assessment and prevention perspective, it is also representative as it dammed the river twice in 2008 and 2016, posing threats to both upstream and downstream areas. We infer that the successive landslides in this region could be caused by the strong tectonic activities: including earthquakes and high average uplifting rate. The results of landslide volume analysis using multi-temporal DEMs, contribute to the landslide mechanism analysis, and suggest that the landslide volume estimation is effected by the landslide type, landslide rupture surface location, and resolution of DEM. We also compare the performance of different empirical models of landslide stability and dam-breach flood parameters and discuss their application during the quick assessment of the potential hazard of the landslide dams. Generally, the successive landslide dams at the Tangjiawan site are caused by the successive landslide reactivations on an anti-dip slope controlled by strong tectonic activity and river erosion, involve with a mass of loose materials of previous landslide deposition, and possess high flood risk to the downstream area. The experience gained in this work can be used to assist the hazard assessment and the planning of the emergency measures for similar landslide dams in the future.

Deformation response regularity of Liujiaba landslide under fluctuating reservoir water level condition

Due to the periodic rising and falling of the reservoir water level, the rock–soil body of bank slope is constantly changing between the saturated and unsaturated status, which changes the limit equilibrium condition of the slope body, resulting in a large number of dormant landslide reactivation and new landslide generation after water impounding operation of the three gorges reservoir. Based on the long-term monitoring data of pore-water pressure, water content, reservoir water level, rainfall and landslide deformation, the deformation response regularity of Liujiaba landslide under the fluctuating reservoir level combined scenario is studied in this paper. The results show that the landslide deformation is mainly in the lower section affected by the fluctuation of the reservoir water. The slide deformation appears in the mid-early stage of the water level declining and during the running of 175 m water level. The deformation is gradually increasing from a slowly to rapidly stage, then slows down and gradually reduces to a relative stopped state. Considering that the variation of the saturation line in the landslide will be influenced by the water level fluctuation rate, the SEEP and SLOPE modules are used with Geo-studio software for the fluctuant reservoir level and response pattern of landslide deformation analysis. The study can be provided as a reference for landslides study of debris aggradational landslide.