Distribution features and formation mechanism of landslides along the middle segment of the Yalong River, China

Catastrophic landslides often occur along the southeastern margin of the Tibetan Plateau because of strong earthquake/faults and heavy rains. In this study, 26 large-scale landslides were collected from the middle segment of the Yalong River to analyze landslide features and possible formation mechanism. The investigation results revealed that landslides featuring a linear distribution along the riverbanks can be classified into three failure types: tensile cracking-sliding, sliding-bending (crushing and buckling), and toppling. Among them, the Xiamajidian landslide at the junction area between the river and the Qianbo fault is being dangerous with obvious deformation, including different subzones and different failure types. The landslide body is delineated into three distinct zones (A, B, and C) based on different deformation features and material compositions. Among them, the Zone A with the largest deformation is dangerous, the front of which is obviously moving toward the river channel. The deformation monitoring data indicated that the 2008 Ms 8.0 Wenchuan earthquake caused only slight disturbances to the Xiamajidian landslide body, but the subsequent 2008 Ms 6.1 Huili earthquake caused the deformation to increase quickly. The distinct-element method is then used to determine the importance of strong earthquakes and heavy rainfall during landslide failure. The results suggest that the landslide may have been broken to form a large landslide event, and finally to form a large landslide dam to block the Yalong River. The results presented in this paper are helpful for disaster prevention and risk evaluation.