中国喜马拉雅山地区滑坡堵江编目及空间特征分析

滑坡堵江数据获取与编目是其区域研究开展的基础。喜马拉雅山脉地处中国西南边陲,新构造运动强烈,滑坡堵江事件频发,在产生巨大经济损失的同时也造成了不良国际影响。鉴于该区区域滑坡堵江现场调查难以开展的问题,本文利用遥感技术、地理信息技术,结合野外验证获取了区内136处滑坡堵江事件的空间位置、基本属性和几何形态,建立了中国喜马拉雅山地区滑坡堵江编目。区内滑坡堵江集中分布在米林、札达、加查、错那、隆子、郎县等县,成因类型以滑坡、崩塌、泥石流为主。基于环境要素信息量计算得出该区滑坡堵江的易发程度随高程、坡度、地震加速度的增大先增大后减小,随地震点密度增大先减小后增大,随构造线密度增大逐渐增大,随与水系距离增大逐渐减小。不同坡向中,西向斜坡更容易诱发滑坡堵江,东南坡向最不容易诱发滑坡堵江。高位高山地貌类型、地层条件中的朗县构造混杂岩组和坚硬岩组,构造分区中的高喜马拉雅分区和雅鲁藏布江分区是滑坡堵江形成的有利条件。对比各环境要素不同类别的信息量取值认为影响该区滑坡堵江事件形成的主要背景因素是高程、地貌类型、地层岩组、构造分区和地震点密度。这些滑坡堵江事件几何参数的研究结果表明坝体长度-坝体面积与滑坡面积-坝体面积之间具有拟合程度较高的乘幂函数关系,而其他参数间的相关性并不突出。     

A new global landslide dam database (RAGLAD) and analysis utilizing auxiliary global fluvial datasets

To address the current data and understanding knowledge gap in landslide dam inventories related to geomorphological parameters, a new global-scale landslide dam dataset named River Augmented Global Landslide Dams (RAGLAD) was created. RAGLAD is a collection of landslide dam records from multiple data sources published in various languages and many of these records we have been able to precisely geolocate. In total, 779 landslide dam records were compiled from 34 countries/regions. The spatial distribution, time trend, triggers, and geomorphological characteristic of the landslides and catchments where landslide dams formed are summarized. The relationships between geomorphological characteristics for landslides that form river dams are discussed and compared with those of landslides more generally. Additionally, a potential threshold for landslide dam formation is proposed, based on the relationship of landslide volume to river width. Our findings from our analysis of the value of the use of additional fluvial datasets to augment the database parameters indicate that they can be applied as a reliable supplemental data source, when the landslide dam records were accurately and precisely geolocated, although location precision in smaller river catchment areas can result in some uncertainty at this scale. This newly collected and supplemented dataset will allow the analysis and development of new relationships between landslides located near rivers and their actual propensity to block those particular rivers based on their geomorphology.

     

清江中下游岸坡稳定性对河流地貌过程的响应

山地滑坡崩塌是岸坡演化过程中的重要地质事件,其发生发展与河流地貌过程密切相关.目前,对滑坡影响因素的研究虽多,但大多局限于滑坡本身的具体研究.通过河流地貌过程研究,进而探讨岸坡稳定性对河道变迁的响应关系,有助于更深入地认识岸坡演化规律,为岸坡稳定性的评价与预测奠定基础.本文采用自然历史分析法和类比法,结合年龄测试手段,...     

正反粒序结构条件下滑坡堰塞坝破坏模式研究

滑坡堰塞坝是大型滑坡堆积体堵塞河道形成的土石坝。正、反粒序结构作为大型远程滑坡所特有的2种具有显著差异的地质结构特征,2种情况下坝体的破坏模式差异及稳定性影响因素亟需试验研究。文章通过室内水槽物理模型实验,对比不同粒径、不同结构的滑坡堰塞坝坝体的破坏过程差异,探究了正、反粒序结构条件下堰塞坝的稳定性差异、破坏模式及影响因素。研究结果表明:（1）堰塞坝破坏模式的变化取决于浸润线在下游坡面的出露位置,相比上游水位有一定的延迟性;（2）正、反粒序堰塞坝的破坏模式取决于坡体渗流与下游坡面临界起动坡降的关系;（3）细砂层的位置分布,不同埋深细砂层的起动临界坡降差异和细砂与中粗砂的孔隙率差异是造成正、反粒序坝体破坏差异的主要原因。该研究成果可为大型滑坡堰塞坝的防灾减灾提供理论指导。     

Knickpoints along the upper Indus River,Pakistan: an exploratory survey of geomorphic processes

This article summarizes an exploratory study carried out to investigate the significance of various geomorphic features on the formation of observed knickpoints along the upper Indus River in northern Pakistan. These features include bedrock lithology, active faults, sediment flux from tributary channels, and landslide dams which have blocked the main channel. The knickpoints and their related geomorphic parameters (channel profile, concavity, drainage area and normalized steepness index, etc.) were extracted from Advanced Spaceborne Thermal Emission and Reflection (ASTER) Global Digital Elevation Models (GDEMs) with 30 m resolution using ArcGIS, River Tools, and Matlab software. A total of 251 major and minor knickpoints were extracted from the longitudinal profile along a ~ 750 km reach upstream of Tarbela Reservoir. The identified knickpoints and their respective normalized steepness index (k_sn values) were compared with bedrock lithology, mapped faults, regional landslide/rockslide inventory, and the locations of historic landslide dams. The analyses revealed that the knickpoints do not correlate with the bedrock lithology except where major unit boundaries coexist with mapped faults, especially in reaches criss-crossed by active thrust faults in the Nanga Parbat Haramosh (NPHM) region. Neither did the river’s major confluences exhibit any notable knickpoints, but the correlations between knickpoints, mapped landslides, and historic rockslide avalanche dams accounted for approximately 75% of the observed knickpoints, a surprising finding. These observations suggest that more detailed studies aided by high resolution data should be undertaken to further explore the characteristics of knickpoints triggered by tectonic uplift, local fault offset, bedrock erodibility, and landslide/rockslide dams.     

Source characteristics of long runout rock avalanches triggered by the 2008 Wenchuan earthquake,China

The May 12, 2008 Wenchuan, China Earthquake which measured M_w = 8.3 according to Chinese Earthquake Administration – CEA (M_w = 7.9 according to the USGS) directly triggered many landslides, which caused about 20,000 deaths, a quarter of the total. Rock avalanches were among the most destructive landslides triggered by this seismic event, and have killed more people than any other type of landslide in this earthquake. The Donghekou rock avalanche, one example of a catastrophic avalanche triggered by the Wenchuan earthquake, occurred in Qingchuan and buried one primary school and 184 houses, resulting in more than 780 deaths, and in addition, caused the formation of two landslide dams, which formed barrier lakes.Combining aerial images (resolution of 0.5 m) with field investigations, this paper lists some parameters of 66 cases in one table, and details source characteristics of six typical cases. It has been found that most of the long runout rock avalanches have source areas with high relief and steep inclination, causing the debris in the travel courses to accelerate. There was also a large amount of saturated Holocene-age loose deposits formed by a river or gully that existed in the travel courses. Comparison studies indicate that saturated Holocene loose deposits in the travel courses could be the most important factor for the causes of the long runout characteristic of the rock avalanches especially when they traveled over gentle or even flat ground surfaces.Furthermore, the relationships among the relief slope gradient, runout and covered area are investigated, and a threshold line for predicting the maximum horizontal runout distance under certain change in elevation is presented.     

高速远程滑坡的地貌学与沉积学研究进展

本文总结了当前有关高速远程滑坡远程机制的研究现状,探讨了滑坡地貌学和沉积学对于揭示高速远程滑坡运动学机理的重要意义。通过梳理前人关于高速远程滑坡堆积形态的分类,分析了高速远程滑坡主要的形态学特征、蕴含的运动学信息以及高速远程滑坡的脱落块体、丘体、脊结构、断层等的地貌结构特征,并进一步指出这些地貌结构的形成主要是滑坡体物质不均匀运动的结果,其受地形和内聚力的影响。高速远程滑坡的沉积学特征明显受到岩性、地形和基底等因素的影响,本文对高速远程滑坡的沉积相模式及其运动学意义进行了分析,并对地层不变性与反序结构两个重要堆积特征进行了讨论。最后,指出高速远程滑坡地貌学与沉积学研究当前主要存在的一些问题,建议将大型物理模拟与数值模拟方法相结合,加强对高速远程滑坡地貌微形态和堆积结构的形成机制研究。     

Numerical SPH analysis of debris flow run-out and related river damming scenarios for a local case study in SW China

A smoothed particle hydrodynamics (SPH) numerical modeling method implemented for the forward simulation of propagation and deposition of flow-type landslides was combined with different empirical geomorphological index approaches for the assessment of the formation of landslide dams and their possible evolution for a local case study in southwestern China. The SPH model was calibrated with a previously occurred landslide that formed a stable dam impounding the main river, and it enabled the simulation of final landslide volumes, and the spatial distribution of the resulting landslide deposits. At four different sites on the endangered slope, landslides of three different volumes were simulated, respectively. All landslides deposited in the main river, bearing the potential for either stable impoundment of the river and upstream flooding scenarios, or sudden breach of incompletely formed or unstable landslide dams and possible outburst floods downstream. With the empirical indices, none of the cases could be identified as stable formed landslide dam when considering thresholds reported in the literature, showing up the limitations of these indices for particular case studies of small or intermediate landslide volumes and the necessity to adapt thresholds accordingly for particular regions or sites. Using the occurred benchmark landslide as a reference, two cases could be identified where a complete blockage occurs that is more stable than the reference case. The other cases where a complete blockage was simulated can be considered as potential dam-breach scenarios.     

Laboratory experiments on three-dimensional deformable granular landslides on planar and conical slopes

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation.     

Landslide hazards triggered by the 2008 Wenchuan earthquake, Sichuan, China

The 2008 Wenchuan earthquake (M _s = 8.0; epicenter located at 31.0° N, 103.4° E), with a focal depth of 19.0 km was triggered by the reactivation of the Longmenshan fault in Wenchuan County, Sichuan Province, China on 12 May 2008. This earthquake directly caused more than 15,000 geohazards in the form of landslides, rockfalls, and debris flows which resulted in about 20,000 deaths. It also caused more than 10,000 potential geohazard sites, especially for rockfalls, reflecting the susceptibility of high and steep slopes in mountainous areas affected by the earthquake. Landslide occurrence on mountain ridges and peaks indicated that seismic shaking was amplified by mountainous topography. Thirty-three of the high-risk landslide lakes with landslide dam heights greater than 10 m were classified into four levels: extremely high risk, high risk, medium risk, and low risk. The levels were created by comprehensively analyzing the capacity of landslide lakes, the height of landslide dams, and the composition and structure of materials that blocked rivers. In the epicenter area which was 300 km long and 10 km wide along the main seismic fault, there were lots of landslides triggered by the earthquake, and these landslides have a common characteristic of a discontinuous but flat sliding surface. The failure surfaces can be classified into the following three types based on their overall shape: concave, convex, and terraced. Field evidences illustrated that the vertical component of ground shaking had a significant effect on both building collapse and landslide generation. The ground motion records show that the vertical acceleration is greater than the horizontal, and the acceleration must be larger than 1.0 g in some parts along the main seismic fault. Two landslides are discussed as high speed and long runout cases. One is the Chengxi landslide in Beichuan County, and the other is the Donghekou landslide in Qingchuan County. In each case, the runout process and its impact on people and property were analyzed. The Chengxi landslide killed 1,600 people and destroyed numerous houses. The Donghekou landslide is a complex landslide–debris flow with a long runout. The debris flow scoured the bank of the Qingjiang River for a length of 2,400 m and subsequently formed a landslide dam. This landslide buried seven villages and killed more than 400 people.     

Stability of landslide dams and development of knickpoints

The Wenchuan earthquake triggered many landslides and numerous avalanches and created 100 odd quake lakes. The quake lakes may be removed or preserved. The removal strategy was applied to several large landslide dams, which were dangerous because massive amounts of water pooled up in the quake lakes. The dams could eventually fail under the action of dam outburst flooding, potentially endangering the lives of people in the downstream reaches. This paper studied the stability of landslide dams and the development of knickpoints by field investigations and experiments, and analyzing satellite images. The study concluded that if landslide dams were preserved, they would develop into knickpoints and act as a primary control of riverbed incision and, thus, reduce the potential of new landslide. The stability of landslide dams depends mainly on the development of the step-pool system and stream power of the flood flow. If a landslide dam consists of many boulders, a step-pool system may develop on the spillway channel of the dam, which would maximize the resistance, consume most of the flow energy and consequently protect the dam from incision. The development degree of the step-pool system is represented by a parameter S _p, which was measured with a specially designed instrument. A preservation ratio of landslide dams is defined as the ratio of preserved height after flood scouring to the original height of the dam. For streams with peak flood discharge lower than 30 m³/s, the preservation ratio is linearly proportional to S _p. For rivers with a peak flood discharge higher than 30 m³/s (30–30,000 m³/s), the minimum S _p value for stable channel increases with log p, in which p is the unit stream power. For a landslide dam with a poorly developed step-pool system, S _p is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam. For preserved landslide dams, sediment deposits in the quake lakes. A landslide dam may develop into a knickpoint if it is stabilized by long-term action of the flow. Large knickpoints can totally change the fluvial processes and river morphology. Uplift of the Qinghai–Tibetan Plateau has caused extensive channel bed incision along almost all rivers. For many rivers, the incision has been partly controlled by knickpoints. Upstream reaches of a knickpoint have a new and unchanging base level. This brings about a transition from degradation to aggradation and from vertical bed evolution to horizontal fluvial process. Multiple and unstable channels are prominent in the reaches, upstream of the knickpoints. If hundreds of landslide dams occurred simultaneously on a reach of a mountain river, the potential energy of bank failure and the slope erosion would be greatly reduced and sediment yield from the watershed may be reduced to nearly zero. The quake lakes may be preserved long term and become beautiful landscapes. Streams with long-term unfilled quake lakes have good aquatic ecology.     

松散土坡结构特征与滑坡堰塞体堆积特征之间的关系试验研究

通过模型实验,探讨了松散土坡3种不同结构特征条件下(均匀坡体(坡体物料均匀混合)、平行坡体(土层成层且层面与滑面平行)和斜交坡体(土层成层且层面与滑面斜交))形成滑坡堰塞体的动力过程和堆积特征,通过分区域取样及三维扫描技术研究了堰塞体的物质分布规律与形态特征。研究结果表明:堰塞体堆积特征与坡体特征存在紧密联系,堰塞体纵向(沿主沟道方向)和横向(沿滑坡运动方向)上的物质分布与坡体纵向和横向的物质分布特征基本对应;在垂向(表层到底部)上,由于不同坡体条件下滑坡的动力过程和机理不同,从而导致堰塞体堆积特征存在一定区别。均匀坡体和平行坡体呈整体启动模式,运动过程中物料间存在垂向渗透和交换作用,导致堰塞体物质在垂向上呈明显的上粗下细反粒序分布特征,堰塞体横剖面多呈平坦型和倾斜型。斜交坡体呈分层启动模式,运动堆积过程中保持原有层序,粗、细颗粒先后启动条件下颗粒间存在推挤、爬升和水平渗透作用,使得堰塞体更加密实且垂向上也呈现反粒序分布特征,横剖面多呈起伏型。本研究为滑坡堰塞体稳定性快速评估和复原滑坡初始状态提供依据。     

Formation process of two massive dams following rainfall-induced deep-seated rapid landslide failures in the Kii Peninsula of Japan

Extreme heavy rainfall due to Typhoon Talas on September 2–4, 2011 in the Kii Peninsula, Japan, triggered numerous floods and landslides. This study investigates the mechanism and the entire process of rainfall-induced deep-seated landslides forming two massive dams in the Kuridaira and Akatani valleys, respectively. The mechanism of the rapid deep-seated landslides is examined through a series of laboratory experiments on samples from sliding surfaces by using undrained high-stress dynamic-loading ring-shear apparatus. The test results indicate that the failure of samples is triggered by excess pore water pressure generation under a shear displacement from 2 to 7 mm with a pore pressure ratio ranging from 0.33 to 0.37. The rapid movement of landslides is mainly attributed to high mobility due to the liquefaction behavior of both sandstone-rich and shale samples. Geomorphic settings and landslide mobility are major contributing factors to the dam formation. Additionally, shear displacement control tests show that a certain amount of shear displacement between 2 and 7 mm along the sliding surfaces of the gravitationally deformed slopes might have led to the failures. Importantly, computer simulation with LS-RAPID software using input parameters obtained from physical experiments is employed to interpret the entire formation process of the abovementioned two landslide dams. The simulation results are examined in accordance with the observed on-site geomorphic features and recorded data to explain the possibility of sliding processes. The results further point out that local failures are initiated from the lower middle part of the landslide bodies where the geological boundary exists. This condition most probably influences the landslide initiation in the two case studies. This research is therefore helpful for hazard assessment of slopes that are susceptible to deep-seated landslides and other sequential processes in areas with geology and geomorphology similar to that of the Kii Peninsula.     

Applying weight of evidence method and sensitivity analysis to produce a landslide susceptibility map

The main purpose of this study is to define the main variables that contribute to the occurrence of landslides in Kimi, Euboea, Greece, and to produce a landslide susceptibility map using the weight of evidence method. For the developed model, a sensitivity analysis is carried out in order to understand the model’s behavior when small changes are introduced in the weight value of the landslide-related variables. Landslide locations were identified from field surveys and interpretation of aerial photographs which resulted in the construction of an inventory map with 132 landslide events, while eight contributing variables were identified and exploited. All landslide-related variables were converted into a 5?×?5-m float-type raster file. These input-raster layers included a lithological unit layer, an elevation layer, a slope angle layer, a slope aspect layer, a distance from tectonic features layer, a distance from hydrographic network layer, a topographic wetness index layer, and a curvature layer. The validation of the developed model was achieved by using a subset of unprocessed landslide data, showing a satisfactory agreement between the expected and existing landslide susceptibility level, with the area under the predictive rate curve estimated to be 0.808. The area under the success rate curve was estimated to be 0.828 indicating a very high classification rate for existing landslide areas. According to the results of the sensitivity analysis, the lithological unit “yellowish gray to white marls” was the most sensitive as it had the highest change in the relative frequency of observed landslides. The overall outcomes of the performed analysis provide crucial knowledge in successful land use planning and management practice and also in risk reduction projects.     

Landslide susceptibility mapping using rough sets and back-propagation neural networks in the Three Gorges, China

In the Three Gorges of China, there are frequent landslides, and the potential risk of landslides is tremendous. An efficient and accurate method of generating landslide susceptibility maps is very important to mitigate the loss of lives and properties caused by these landslides. This paper presents landslide susceptibility mapping on the Zigui-Badong of the Three Gorges, using rough sets and back-propagation neural networks (BPNNs). Landslide locations were obtained from a landslide inventory map, supported by field surveys. Twenty-two landslide-related factors were extracted from the 1:10,000-scale topographic maps, 1:50,000-scale geological maps, Landsat ETM + satellite images with a spatial resolution of 28.5 m, and HJ-A satellite images with a spatial resolution of 30 m. Twelve key environmental factors were selected as independent variables using the rough set and correlation coefficient analysis, including elevation, slope, profile curvature, catchment aspect, catchment height, distance from drainage, engineering rock group, distance from faults, slope structure, land cover, topographic wetness index, and normalized difference vegetation index. The initial, three-layered, and four-layered BPNN were trained and then used to map landslide susceptibility, respectively. To evaluate the models, the susceptibility maps were validated by comparing with the existing landslide locations according to the area under the curve. The four-layered BPNN outperforms the other two models with the best accuracy of 91.53 %. Approximately 91.37 % of landslides were classified as high and very high landslide-prone areas. The validation results show sufficient agreement between the obtained susceptibility maps and the existing landslide locations.     

Numerical runout simulation of debris avalanches in the Faroe Islands, North Atlantic Ocean

The Faroe Islands in the North Atlantic Ocean are susceptible to flow-type landslides in coarse-grained highly organic colluvium. Following several hazardous debris avalanche events, research work has been initiated to quantify landslide risk. A central task in this work is to predict landslide runout behavior. From numerical simulation of four debris avalanches, this study provides a first screening of which rheology and appertaining input parameters best predict runout behavior of debris avalanches in the Faroe Islands. Three rheologies (frictional, Voellmy, and Bingham) are selected and used for individual back analysis of the events in the numerical models BING and DAN3D. A best fit rheology is selected from comparing predicted and observed landslide runout behavior. General back analysis to identify the optimal input parameters for the chosen rheology is performed by cross validation, where each debris avalanche is modeled with input parameters from the three other events. Optimal input parameters are found from the model run producing the most accurate runout length and velocity. The Bingham is selected as the best fit rheology, a result differing from similar studies of coarse-grained landslides. A reason for why particularly the frictional rheology proves unsuitable is its tendency to produce too long runout lengths of the low-weight runout material, a result showing important limitations for using the frictional rheology in DAN3D. Optimal Bingham input parameters are τ _y ?=?980 Pa and μ _b ?=?117 Pa/s. However, future studies performed in 2D models are needed for precise parameterization before results can be used for landslide risk assessment.     

Landslides triggered by slipping-fault-generated earthquake on a plateau: an example of the 14 April 2010, Ms 7.1, Yushu, China earthquake

On 14 April 2010 at 07:49 (Beijing time), a catastrophic earthquake with Ms 7.1 struck Yushu County, Qinghai Province, China. A total of 2,036 landslides were interpreted from aerial photographs and satellite images, verified by selected field checking. These landslides cover about a total area of 1.194 km². The characteristics and failure mechanisms of these landslides are presented in this paper. The spatial distribution of the landslides is evidently strongly controlled by the locations of the main co-seismic surface fault ruptures. The landslides commonly occurred close together. Most of the landslides are small; there were only 275 individual landslide (13.5 % of the total number) surface areas larger than 1,000 m². The landslides are of various types. They are mainly shallow, disrupted landslides, but also include rock falls, deep-seated landslides, liquefaction-induced landslides, and compound landslides. Four types of factors are identified as contributing to failure along with the strong ground shaking: natural excavation of the toes of slopes, which mean erosion of the base of the slope, surface water infiltration into slopes, co-seismic fault slipping at landslide sites, and delayed occurrence of landslides due to snow melt or rainfall infiltration at sites where slopes were weakened by the co-seismic ground shaking. To analyze the spatial distribution of the landslides, the landslide area percentage (LAP) and landslide number density (LND) were compared with peak ground acceleration (PGA), distance from co-seismic main surface fault ruptures, elevation, slope gradient, slope aspect, and lithology. The results show landslide occurrence is strongly controlled by proximity to the main surface fault ruptures, with most landslides occurring within 2.5 km of such ruptures. There is no evident correlation between landslide occurrences and PGA. Both LAP and LND have strongly positive correlations with slope gradient, and additionally, sites at elevations between 3,800 and 4,000 m are relatively susceptible to landslide occurrence; as are slopes with northeast, east, and southeast slope aspects. Q₄ al-pl, N, and T₃ kn ¹ have more concentrated landslide activity than others. This paper provides a detailed inventory map of landslides triggered by the 2010 Yushu earthquake for future seismic landslide hazard analysis and also provides a study case of characteristics, failure mechanisms, and spatial distribution of landslides triggered by slipping-fault generated earthquake on a plateau.     

Evaluation of potential landslide damming: Case study of Urni landslide,Kinnaur, Satluj valley,India

This work aims to understand the process of potential landslide damming using slope failure mechanism,dam dimension and dam stability evaluation. The Urni landslide, situated on the right bank of the Satluj River, Himachal Pradesh(India) is taken as the case study. The Urni landslide has evolved into a complex landslide in the last two decade(2000-2016) and has dammed the Satluj River partially since year 2013,damaging ～200 m stretch of the National Highway(NH-05). The crown of the landslide exists at an altitude of ～2180-2190 m above msl, close to the Urni village that has a human population of about 500.The high resolution imagery shows ～50 m long landslide scarp and ～100 m long transverse cracks in the detached mass that implies potential for further slope failure movement. Further analysis shows that the landslide has attained an areal increase of 103,900 ± 1142 m^2 during year 2004-2016. About 86% of this areal increase occurred since year 2013. Abrupt increase in the annual mean rainfall is also observed since the year 2013. The extreme rainfall in the June, 2013; 11 June(～100 mm) and 16 June(～115 mm),are considered to be responsible for the slope failure in the Urni landslide that has partially dammed the river. The finite element modelling(FEM) based slope stability analysis revealed the shear strain in the order of 0.0-0.16 with 0.0-0.6 m total displacement in the detachment zone. Further, kinematic analysis indicated planar and wedge failure condition in the jointed rockmass. The debris flow runout simulation of the detached mass in the landslide showed a velocity of ～25 m/s with a flow height of ～15 m while it(debris flow) reaches the valley floor. Finally, it is also estimated that further slope failure may detach as much as 0.80 ±0.32 million m^3 mass that will completely dam the river to a height of 76±30 m above the river bed.     

Landslide susceptibility analysis using probabilistic likelihood ratio model—a geospatial-based study

The crucial and difficult task in landslide susceptibility analysis is estimating the probability of occurrence of future landslides in a study area under a specific set of geomorphic and topographic conditions. This task is addressed with a data-driven probabilistic model using likelihood ratio or frequency ratio and is applied to assess the occurrence of landslides in the Tevankarai Ar sub-watershed, Kodaikkanal, South India. The landslides in the study area are triggered by heavy rainfall. Landslide-related factors—relief, slope, aspect, plan curvature, profile curvature, land use, soil, and topographic wetness index proximity to roads and proximity to lineaments—are considered for the study. A geospatial database of the related landslide factors is constructed using Arcmap in GIS environment. Landslide inventory of the area is produced by detailed field investigation and analysis of the topographical maps. The results are validated using temporal data of known landslide locations. The area under the curve shows that the accuracy of the model is 85.83%. In the reclassified final landslide susceptibility map, 14.48% of the area is critical in nature, falling under the very high hazard zone, and 67.86% of the total validation dataset landslides fall in this zone. This landslide susceptibility map is a vital tool for town planning, land use, and land cover planning and to reduce risks caused by landslides.     

金沙江上游快速隆升河段复杂结构岩体灾变特征与机理

横断山脉北麓金沙江上游河段沟壑纵横,水能资源丰富。中、晚更新世以来,快速隆升的新构造活动导致该河段复杂结构岩体在重力场的持续作用下灾变频繁。笔者阐述了该河段高地应力的基础地质背景与金沙江板块构造结合带蛇绿岩套的复杂结构岩体基本特征,提出了快速隆升河段的基本认知,建议将≥5 mm/a作为快速隆升河段的界限值;列举了21.4 km河段内不同时期、不同类型4处大规模堵江事件的证据和基本特征,阐述了其与快速隆升之间的关系;运用地质过程机制法分析了4个堵江体的致灾机理,指出早期堵江残体为未来人类工程活动的潜灾体。