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In the past 20 years, Lebai gully (Linzhi, Tibet, China) has been affected by several debris flow events. These debris flow events caused the blockage of three-quarters of the river channel at the mouth of the Lebai gully, threatening thousands of acres of cultivated land, houses, and residents' property in the upper reaches of the Yarlung Tsangpo River. However, few investigations have been carried out on the debris flows in the Lebai gully, and the triggering mechanism of Lebai debris flows remains elusive. In this paper, we presented a detailed demonstration of the geological environment and geomorphological features of the Lebai Basin, and a detailed geohazard history of the Lebai gully was collected and presented based on interviews with local villagers. To provide information on the lithological, hydrological, and geotechnical characteristics of the terrain in Lebai gully, the electrical resistivity tomography (ERT) method was carried out to research the subsurface characteristics of debris flow fans. The ERT results illustrated the two-layered vertical strata of the debris fan, and the shallow layer of relatively low resistivity, which has thicknesses of 5–18 m, could be described as Quaternary colluvial deposits, while the deep layer of relatively high resistivity could be considered Precambrian bedrock. Taking a relatively large-scale debris flow on August 20, 2003, as an example, a detailed discussion was carried out on the possible factors triggering this event, and it was found that the Lebai debris flows were closely related to pre-event rainfall, air temperature, and antecedent earthquakes. Moreover, with the intention of evaluating the future risk of river blockage and helping to make rational decisions on developing suitable mitigation measures, the unstable deposits found in field investigations were generalized to geometric models according to their geometric characteristics, and the volumes of these unstable materials in each location were estimated using digital elevation models and geometric spatial analysis methods. A dynamic model named RAMMS was used to predict these unstable materials' dynamic processes and final deposit characteristics. The simulation results revealed a great possibility that the Yarlung Tsangpo River will be blocked at the mouth of Lebai gully in the future, and it is necessary to take further mitigation measures. The research in this paper contributes to a better understanding of the debris flows in the Lebai Basin and provides meaningful and valuable information for debris flow hazard mitigation in the future. [ABSTRACT FROM AUTHOR]

On September 7, 2017, a slope failure occurred in Zhimei village, Chengduo County, Qinghai Province, China. This event involved the failure of 2.4 × 104 m3 of soil from the source area. The displaced mass traveled about 480 m with a vertical distance of approximately 80 m. Based on field investigation and numerical analysis, the failure mechanism and propagation process of Zhimei earthflow were analyzed. The results indicated that seasonal freeze–thaw cycles and sustained rainfall in the rainy season before the slope failure could be the leading causes of slope instability, and a short-term cold snap that coincided with this slope failure may play a secondary role in causing the event. The DAN3D simulation results estimated that the movement process of Zhimei earthflow could last for approximately 800 s with an average displacement rate of 0.6 m/s. A combined Bingham model demonstrated the best performance in reproducing this event. The results in this paper could contribute to drawing some valuable conclusions, which can be used in the future for enhancing the accuracy of hazard assessment for areas with topographical and climatic characteristics similar to those of this case on the Qinghai–Tibet Plateau. [ABSTRACT FROM AUTHOR]

On April 9, 2000, a long run-out landslide occurred in Yigong, Bomi county, Yarlung Zangbo Grand Canyon, China. The displaced materials traveled approximately 10 km with an elevation difference of 3 km, and finally generated a barrier lake at the toe of the mountain. The landslide and the collapse of the associated landslide dam killed 30 people, left more than 100 people missing, and destroyed several bridges. A combined debris avalanche-dam break flood simulation was performed in this study to better understand the long run-out mechanism and behaviors of such an event. The dynamic model DAN3D was used to simulate the run-out process of the sliding mass, while the Computational Fluid Dynamics software FLOW-3D was used to simulate the duration of landslide dam break and subsequent outburst flood propagation. Output data from the DAN3D simulation were used as input parameters for landslide dam modeling in FLOW-3D. Simulated results indicated that the duration of the landslide movement was estimated at 300 s with a maximum velocity of 90 m/s. Also, the maximum flow of the outburst flood at the Tongmai bridge was approximately 130,000 m3/s. The observed phenomena and measured data in situ verified the validity of the numerical simulation. It is expected that the work conducted in this study could help improve the understanding of the chain disaster of the rock slide-debris avalanche and subsequent dam-break flood. [ABSTRACT FROM AUTHOR]