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On 28 August 2017, a large catastrophic rock avalanche occurred in Nayong, Guizhou Province, China. It claimed 35 lives and caused large property losses. The Nayong rock avalanche provides a rare opportunity to infer the dynamic fragmentation of rock masses from deposits. Field surveys combined with an uncrewed aerial vehicle image analysis system were performed to investigate the particle size and shape distribution along the runout path of the Nayong rock avalanche. The Weibull particle size distribution (PSD) model was tested and possesses the highest accuracy and capability over the entire range of the Nayong rock PSD, and it shows that the median size (D50) values of the particles range from 0.16 to 16.31 m along the runout path. Moreover, the evolution of D50 along the runout path confirms that the degree of rock fragmentation varies greatly in different regions. Additionally, the relative breakage (BR) of particles in the deposition area is 0.191. Particle R values increase significantly from 0.55 to 0.78 along the runout path, which indicates that the rock grinding (shape change) process continuously occurs throughout the avalanche path. The image analysis results confirm that the dominance of rock fragmentation and grinding alternates during granular flow transport. Based on these results, the classic fragmentation‐spreading model for long‐runout rock avalanches is optimized by taking into account the method by which grinding rocks increases the speed of avalanches. Plain Language Summary: On 28 August 2017, a large catastrophic rock avalanche occurred in Nayong, Guizhou, China. In this paper, a field survey based on High‐resolution uncrewed aerial vehicle technology and image‐analysis system was performed to study the characteristics of particle size and shape distribution and the long‐runout behavior of large rock avalanches. A fragmentation‐spreading model for long‐runout behavior of rock avalanches proposed by Davies was optimized by incorporating the mechanisms involving internal friction reduction caused by dynamic grinding process. The internal friction of particles dropped correspondingly during transport and resulted in the increase of spreading distance. Key Points: An image analysis system for the large‐scale field investigation has been applied to morphometric measurements of rock avalanchesThe degree of rock fragmentation gradually decreases with the travel distance of rock mass in a rock avalancheRock grinding gradually replaces the role of rock fragmentation and reshapes the particles as the travel distance increases [ABSTRACT FROM AUTHOR]

On 23rd July 2019, a catastrophic long-runout basalt landslide was triggered by a heavy rainfall in Shuicheng county, Guizhou, China. The sliding mass transformed into a debris avalanche during the runout process traveled approximately 1250 m with an elevation difference of 465 m and finally caused 52 casualties. To improve the ability of risk assessment of such a basalt long-runout landslide, scanning electron microscope (SEM) tests combined with detailed field investigation were conducted to investigate the failure mechanism of the Shuicheng landslide in terms of micro and macro perspectives. The results indicated that the cause of the Shuicheng landslide is the combination of rock mass characteristics (differential weathering and fragmented cataclastic structure), weak tuff intercalation, tectonic structural plane, and human activities, while rainfall is the primary inducing factor. Moreover, a RAMMS simulation and electrical resistivity tomography (ERT) tests were performed to research the disaster-causing behaviors and deposit characteristics of this event. The selected rheological parameters are determined based on multi-source data collaboration. The total duration of the landslide movement was estimated at 60 s with a maximum velocity of approximately 36 m/s, and the final deposit distribution was in good agreement with the ERT test results and seismic signal analysis results. The work conducted in this study is expected to help improve the understanding of the initiation and disaster-causing mechanisms of basalt long-runout landslides and provide valuable information for the prediction of long runout landslides movement distance in the Guizhou, China. [ABSTRACT FROM AUTHOR]

A rock avalanche that destroyed 23 houses and killed 35 people occurred on 28 August 2017, Nayong, SW China. Combined with the dynamic parameters from seismic signal inversion, a discrete element model, MatDEM was used to determine the rock avalanche's kinematic behavior. Although the dynamic process obtained through inversion will be disturbed by factors, such as rockfall from the source area, by comparing the velocity of rock avalanche versus horizontal distance traveled, the best combination of parameters was selected from different values given. The dynamic process obtained by modeling was compared with the nearest seismometer frequency distribution spectrum, showing that the dynamic process is in good agreement with those parameters inverted from seismic signals. The simulation results show that the movement process lasted for nearly 40 s, with a maximum speed of 40 m/s. This model of selecting parameters contributes to explain the dynamic processes of similar rock avalanche more accurately and is of great significance to the hazard prediction in the karst area. [ABSTRACT FROM AUTHOR]

On July 23, 2019, a large catastrophic landslide occurred in Shuicheng, Guizhou, China. It was a rapid and long run-out landslide that resulted in more than 50 casualties. The displaced materials traveled an approximate distance of 1250 m, with a descending height of around 465 m. In this paper, seismic record analyses and numerical simulation were conducted to determine the run-out behavior of the Shuicheng landslide. To determine the main characteristics of the landslide, geological and climatic settings were obtained by conducting a detailed field survey. The DAN3D model was used to simulate the propagation and run-out process of the landslide. It was observed that a combined Frictional-Voellmy model provides assuring results in simulating the Shuicheng landslide. The total duration of the landslide is 60 s with an average velocity of 20 m/s. The maximum velocity is estimated to be 40 m/s along the right bank of the valley, while a high initial velocity of 24 m/s was recorded at the initiation of the landslide. Seismic records obtained from the nearby seismic stations were used to calculate the location of the event and interpret the dynamic process of the landslide. The Arias intensity, Hilbert-Huang transform, and Empirical mode decomposition were used to obtain a detailed time history of the landslide. The results of the numerical simulation and seismic record analyses are expected to portray the process of similar landslides. This will improve the accuracy of landslide hazard mapping in the region. [ABSTRACT FROM AUTHOR]

Large impulse waves are generated when a highly mobilized landslide impacts a water body along the runout path. On August 27, 2014, a massive landslide occurred in Fuquan, Guizhou, China and induced an impulse wave upon contact with a quarry lake. The landslide and its associated impulse wave were a multiphase and multicomponent mixture that collectively destroyed two villages. The present study provides insights into multiphase dynamic analysis by employing an existing 3D coupled discrete element modeling and computational fluid dynamics approach to model a case study of the Fuquan landslide and its impulse wave. EDEM and Fluent were two-way coupled by an application programming interface, which transferred data between the models to simulate subaerial movement and impulse wave generation. The simulated results indicate a maximum velocity of 31.7 m/s achieved by the subaerial movement and a runout duration of 39 s. The detached mass entered the quarry lake at a velocity of 24.3 m/s, at t = 7.1 s after the landslide initiation. Energy was transferred between the sliding mass and lake water, and the generated water wave rushed toward the opposite slope. The generated wave had a run-up of 28.4 m and traveled approximately 90 m in the lateral direction, with a maximum dynamic pressure of 3.03 MPa. Qualitative validation of the present model was performed using Fritz's experimental setup for wave generation, and the velocity evolution was physically verified. This study provides calibrated parameters for the forward simulation of similar cases of landslide-induced impulse water waves and related hazard zonation. • Fuquan rock avalanche moved rapidly and induced a powerful water wave. • The generated water wave caused fatalities far beyond the avalanche. • Coupled CFD-DEM method simulated the dynamic behaviors of the chain disaster. • Fuquan rock avalanche-related water wave has a maximum runup of 28.4 m. [ABSTRACT FROM AUTHOR]

On 28th August 2017, a disastrous rock avalanche occurred in Nayong, Guizhou, China. This catastrophic event killed 35 people and destroyed 23 houses. In this study, the failure process of the avalanche was analyzed using UAV video footage and seismic signal recordings obtained for the pre- and post-failure stages of the landslide. To better understand the possible mechanism of the avalanche and its dynamic characteristics, a numerical simulation was conducted using a dynamic model (DAN3D) to simulate the runout behaviour of the displaced materials. Simulated results indicate that the failure process of the Nayong rock avalanche lasted approximately 30 s; the duration of the failure process is close to that from the UAV video footage and seismic signal recordings (35 s). The duration of movement during the landslide process is estimated to be approximately 90 s with a maximum velocity of 40 m/s. The combined frictional-Voellmy model delivered the most accurate results when simulating this event. The selected models and parameters are expected to aid in clarifying the propagation processes of similar rock avalanches and thus improve the accuracy of hazard prediction in mountainous karst areas. • Nayong rock avalanche is a long run-out one. • A UAV video and a recorded seismic signal were analyzed. • Rock avalanche was well simulated by DAN3D. • DAN3D simulation results were verified by the seismic signal. [ABSTRACT FROM AUTHOR]