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Geomorphological and sedimentological characteristics are key evidences for understanding the emplacement mechanisms of rock avalanches. Based on remote sensing, photogrammetry, and field surveys, the depositional characteristics of the Alasu rock avalanche (ARA) in southern Tianshan, China, were investigated in detail. It is reached that the ARA has a detached rock mass volume of ~ 93 × 106 m3 and propagated 3874 m on rugged terrain with a drop height of 1030 m. Large rock blocks (95,598 rock blocks with sizes ≥ 0.5 m) are widely distributed on the deposit surface. There is no decreasing trend in block size with travel distance for these rock blocks, while jigsaw and sibling structures of megablocks commonly occur in the carapace facies. The size and structural features of megablocks demonstrate that the carapace facies underwent a passive emplacement process with low degrees of fragmentation and disturbance. Furthermore, a series of surficial landforms, including irregular platforms, minor scarps, lateral levees, run-ups, ridges, and troughs, are preserved in the rock avalanche deposit. The most remarkable features are the large, subparallel, curved longitudinal ridges with continuous directional variations and three run-up traces. Extensions of these ridges indicate that the avalanche mass experienced a continuous extension-dominated process in emplacement due to its momentum transfer effect and high energy propagation. These observations and analyses may elucidate the emplacement mechanisms of rock avalanches in rugged landscapes. [ABSTRACT FROM AUTHOR]

The Xieliupo landslide is a typical large-scale active landslide in Zhouqu, China, in the Pingding-Huama fault zone that has slid eight times since the beginning of the twentieth century. The landslide has caused catastrophic environmental, economic, and life losses in the area. In this study, combining the geomorphological field surveys, Unmanned Aerial Vehicle (UAV) mapping, interpretation of optical images, InSAR, and Cosi-Corr (Co-registration of Optically Sensed Images and Correlation) monitoring analysis, we conducted insights into the deformation kinematics of large Xieliupo landslide. The Xieliupo landslide has the characteristics of graded sub-activity with eight secondary landslides. The secondary landslides I and II in the upper parts are loess slide-flow with a moving pattern of creep–rip–push on the condition of steep gradient and the triggering of intense precipitation. The middle part was divided into two sides by a relatively stable ridge, where the loess rotational landslides III and collapse VI in the northern side are controlled by low-lying terrain in the valley, and the landslides IV and V are moderately active under the influence of steep gradient and compression from the landslides I and II. The secondary landslides VII and VIII in the toe are relatively slightly active with a gentle slope gradient influenced by road construction and Bailong River erosion. Time-series InSAR deformation from 2015 to 2020 revealed a close positive correlation between accelerating displacements and increasing precipitation. The deformation response characteristics of cascade collapse retreat and fluctuating acceleration of the Xieliupo landslide to heavy rainfall were revealed. The seismic activity is one probable factor contributing to the reactivated displacement of Xieliupo landslide. Notably, the intense rainfall on August 13, 2020, triggered the maximum displacement of 5.93 m in a sliding direction of 319° (NW) at secondary landslide II. This study significantly provides new insight into the deformation characteristics and kinematics of Xieliupo and reference for catastrophic landslide hazard mitigation. The proposed technique strategy can be used for analyzing similar large complex landslides in other mountainous regions. [ABSTRACT FROM AUTHOR]

Knowledge of kinematics is crucial for understanding landslide mechanisms and assessing hazards. However, characterizing landslide kinematics is often challenging because landslides are sudden events with spatial and temporal coverage. Combining field investigations and remote sensing, the present study reveals the kinematic features, evolution processes, and triggering mechanism of a translational debris slide (the Tonghua landslide) that occurred on August 8 of 2017 in Sichuan Province, China. Based on digital orthophoto maps and digital elevation models derived from unmanned aerial vehicle photogrammetry, 3 years of post-failure kinematics were surveyed in detail. The landslide body experienced moderate-velocity (1.19–3.98 m/d) to slow-velocity (33.2–205.5 mm/d) sliding, eventually entering a period of very-slow-velocity (0.1–1.0 mm/d) sliding. A long-term pre-failure creeping process in the source area of the landslide was detected by interpreting interferometric synthetic aperture radar data and satellite images. At the front part of the source area, the observed deformation velocity was 15–25 mm/year between November 7, 2014 and July 30, 2017. Additionally, the source area of the landslide was found to be located on a hollow slope within a cirque catchment of ~ 67,500 m2. This complicated topographic feature promoted groundwater infiltration and long-term slope creeping; indeed, the 2008 Wenchuan earthquake may have aggravated surface cracking and soil weakening. Long-term creep of the slope caused cracking, saturation, and deformation of the soil body. Finally, seismic effects caused by tunnel blasting triggered sliding of the deformed soils. [ABSTRACT FROM AUTHOR]

At 8:40 p.m. (Beijing time) on July 23, 2019, a large landslide occurred at Jichang, a village in Shuicheng, Guizhou Province, China, resulting in 42 deaths, 9 missing people, and 21 buildings buried. Field investigation and unmanned aerial vehicle (UAV) photography allow us to characterize this slope failure and analyze its process and causes. Initially, the materials detached from the mountainside and slid over from the slope. Then, the sliding materials partly accumulated in the middle and upper parts of the slope which were blocked by a convex terrain. The rest turned into a high-speed debris flow, divided by the stable block, and descended along two existing gullies at high velocity, and finally decelerating and accumulating. Based on the high-resolution post-sliding DEM data, the original topography of the study area was reconstructed to estimate the volume of the landslide that was about 1,500,000 m3. Based on a first-order evaluation of the landslide kinematics, the whole sliding process of this event lasted about 60 s, the maximum speed was about 25 m/s, and the average speed was 16.6 m/s, indicating a typical high-speed long-runout debris flow. Analysis suggests that continuous heavy rainfall was the dominant factor to trigger this landslide, and the loose weathered regolith and special local topography were the basic intrinsic factors for this event. [ABSTRACT FROM AUTHOR]

On July 23, 2019, a large-scale landslide occurred in Jichang town, Shuicheng County, Liupanshui City, Guizhou Province in China. The landslide, which moved along two gullies, resulted in strong punching-shear, induced scarping on vegetation and large destruction of houses, and finally formed a deposit with a volume of 2 × 106 m3. This research aims to understand the effect of topography on landslide kinematics. To achieve this aim, a detailed field investigation was first carried out with an unmanned aerial vehicle (UAV) aerial photography survey, resident interviews, and field sampling. The rainfall analysis indicates the effective rainfall within 7 days before landslides was 70.14 mm which exceeded the rainfall threshold of 54.3 mm in this region, which finally triggered the landslide. Traditional soil mechanic tests were then performed to identify the soil properties of the source material. Combined with numerical simulation using the nonlinear shallow water equation, the whole process of landslides was divided into four stages: instability stage, acceleration stage, transformation stage, and impact and accumulation stage. The simulations results show the landslide block slid with a low velocity of 8 m/s for about 100 m. Then, Froude number of landslide increases from 2 to 3 when passing the high and steep terrain, indicating that landslide change to inertial dominated with potential same Froude behavior of classic debris flow. The rupture mass slid with the peak velocity of 23 m/s and diverged in two gullies and ran out for about 600 m. The maximum velocity is 23 m/s in east gully while only 15 m/s in west gully. Compared with deep and incised valleys in the west, shallow and straight valley in the east decreases the deposit depth and further increases the velocity of landslide material with increased runout distance. This research may provide a fast flow path of back analyzing geo-hazards on complex terrain and serve as a basis for future research on long runout landslides. [ABSTRACT FROM AUTHOR]

Rock avalanches represent a serious risk for human lives, properties, and infrastructures. On June 24, 2017, a catastrophic landslide destroyed the village of Xinmo (Maoxian County, Sichuan, China) causing a large number of fatalities. Adjacent to the landslide source area, further potentially unstable masses were identified. Among them, a 4.5-million m3 body, displaced during the landslide event by about 40 m, raised serious concerns. Field monitoring and a reliable secondary risk assessment are fundamental to protect the infrastructure and the population still living in the valley. In this framework, the use of distinct element methods and continuum model methods to simulate the avalanche process was discussed. Various models (PFC, MatDEM, MassMov2D, Massflow) were used with the aim of reproducing the Xinmo landslide and, as predictive tools, simulating the kinematics and runout of the potentially unstable mass, which could cause a new catastrophic event. The models were all able to reproduce the first-order characteristics of the landslide kinematics and the morphology of the deposit, but with computational times differing by several orders of magnitude. More variability of the results was obtained from the simulations of the potential secondary failure. However, all models agreed that the new landslide could invest several still-inhabited buildings and block the course of the river again. Comparison and discussion of the performances and usability of the models could prove useful towards the enforcement of physically based (and multi-model) risk assessments and mitigation countermeasures. [ABSTRACT FROM AUTHOR]