Fragmentation is a very common phenomenon in high-speed long runout landslides, which is not only the basis of the granular flow hypothesis, but also related to dissipation and transmission of energy. In order to examine the kinematic and fragmentation characteristics of long runout landslides, the Walai rock avalanche was studied as an example. According to the remote sensing interpretation, field investigation and grain size tests, the geomorphologic features, sedimentary structures, kinematic processes and fragmentation characteristics of Walai rock avalanche were analyzed and discussed. The geomorphic structures were quantitatively analyzed based on the high precision digital elevation model built by unmanned aerial vehicle measurement. The contour map and bedrock data were used to reconstructed the pre-topography and the volume of this rock avalanche was estimated. The results indicated that the Walai rock avalanche was controlled by the rock joints, its horizontal travel distance reaches 3480m (H/L = 0.32) and the accumulated volume is about 5.12×10^7 m^3. The geomorphic structures of the Walai rock avalanche is characterized by trimlines, huge hummocks, longitudinal ridges and compressed ridges. These geomorphologic structures indicated that the Walai rock avalanche moved in the northeast direction at first, and turned to the north when it encountered the eastern mountain. The carapace facies of Walai rock avalanche is thin, and the blocks is about 30cm, which was significantly influenced by the joints. The sedimentary features in body facies, including the stratified layers, jigsaw structures, directional arrangements and shear failure of block, indicating that the rock avalanche moved as a laminar flow and there were collision and shear actions during the movement. The change in the size of blocks in body facies suggested that the fragmentation mainly formed due to the impact actions from the source area to the toe of the transition zone; and the fine grain distribution characteristics and absence of obvious shear zone indicated that the internal shear behavior during the radial motion stage was not stronger than that of the former.
