The morphology and sedimentology of the Walai rock avalanche in southern China, with implications for confined rock avalanches

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 413; p. 108346
• Main Authors: Chen, Ruichen, Chen, Jian, Xu, Hui, Cui, Zhijiu, He, Qing, Gao, Chunyu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2022
• Subjects: Confined; Emplacement processes; Rock avalanche; Tibetan Plateau; Tibetan Plateau; Emplacement processes; Rock avalanche; Confined
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2022.108346

The Walai rock avalanche (H/L ratio = 0.32), which was laterally and frontally confined occurred in the high mountainous areas of the eastern Tibetan Plateau. According to the field investigation and optically stimulated dating, the initial rock slope failure was determined to be a wedge failure controlled by bedding and two joint sets at approximately 38 ka ago. Based on the topography reconstruction, the deposited volume of this rock avalanche was estimated at 5.2 × 107m3, which was 1.24 times the mass detached from the source area. We observed and mapped trimlines, longitudinal ridges, arched ridges, and lateral ridges associated with the rock avalanche. We also observed well-developed sedimentary features, including carapace facies, body facies, stratified structures, jigsaw fractures, directional arrangements, shear-damaged rock clasts, and interior folds. Measured grain size distributions indicated that the Walai rock avalanche fragmented within a relatively short travel distance after detachment from the source area, with no progressive reduction of grain sizes during the subsequent movement. Based on the morphological and sedimentary features, the emplacement process of the Walai rock avalanche was determined to be controlled by the local terrain and could be divided into four stages: an initiation stage (detachment), an accelerating stage (fragmentation), a longitudinal compression stage (momentum transfer), and a spreading stage (shearing). •A confined rock avalanche that swerved and blocked the river was analyzed.•The trimlines provided evidence for the emplacement process of the rock avalanche.•A contour reconstruction method was used to estimate the ancient landslide volume.•Weak fragmentation effect was found in the later stage of rock avalanche movement.