Characteristics and transport mechanism of the Nyixoi Chongco rock avalanche on the Tibetan Plateau, China

Abstract

For studying rock avalanches, complex surficial and internal characteristics have been regarded as important indicators for understanding avalanche transport mechanism. In the present study, deposits of a massive Holocene rock avalanche, termed the Nyixoi Chongco rock avalanche, located on the Lhasa Terrane of Tibetan Plateau in China are investigated, based on a combination of remote sensing data and in-situ observations. It is revealed that abundant surface landforms, including Toreva blocks, longitudinal and transverse ridges, en echelon ridges, and hummocks, are commonly developed. Corresponding to these surface morphologies, a series of internal sedimentary structures, including jigsaw structures, inner shear zones, aligned clasts, diapiric structures, convoluted laminations, and basal décollements, are also well developed. Through an analysis of these surficial and internal characteristics, we propose that a rapid motion, similar to a laminar flow, most likely occurred after the avalanche mass detaching from the source area. In this process, the detached avalanche mass was mainly emplaced by a frictional, simple shear process characterized by a bulldozing effect that occurred between the sliding mass and the substrate. From the proximal to the distal sections of the avalanche, the transport of the rock mass can be classified into four major processes: an extension-dominated sliding process in the transition zone, a compression-dominated sliding process in subzones III-1 and III-2 of the accumulation zone (III), a sliding process co-dominated by compression and lateral spreading in subzone III-3, and a rapid radial spreading process in subzone III-4. The results of our study provided an improved understanding of the transport mechanisms of this rock avalanche.