Dynamics and emplacement mechanisms of the successive Baige landslides on the Upper Reaches of the Jinsha River, China

Two successive Baige landslides are presented in this study to investigate the dynamics and emplacement mechanisms. Field survey shows that the deposit characteristics of the first landslide are affected by the extremely fractured rock masses and the complex spatial distribution of lithologies in the source area. This deposit consists of abundant angular megablocks on the surface supported by clasts, with a relatively abundant content of rubble ranging from micrometre to decimetre sizes, and rarely well-preserved original stratigraphic sequence, diapiric structure, and convoluted structure. These sedimentological characteristics imply that a simple differential shear process, induced by compression, is distributed through the entire avalanche masses with low internal disturbance during the emplacement of the first landslide. The three-dimensional discrete element simulations show that: (i) the first landslide reaches its maximum average velocity of 41 m/s in ~28 s and eventually is bulldozed to a halt in the river within ~80 s. (ii) The second landslide is controlled by entrainment, which impedes the avalanche from further accelerating, and simultaneously imparts kinematic energy to the substrate, eventually becoming entirely mobilized and reaching a maximum average velocity of 35 m/s in ~36 s. In the dynamic process of the second landslide, the significant entrainment-induced enlarged volume (its entrainment ratio reaches 3.3) is associated with the steep concave terrain, water-bearing substrate and lower-roughness substrate basal boundary, and overloading-impact-induced erosion is proposed to be the most significant contribution to this entrainment. •The stratigraphic preservation, diapiric and convoluted structures are observed in rock avalanche deposits.•A simple differential shear is proposed as the main emplacement form.•Discrete element simulations support the landslide process reconstructions•Overloading-impact-induced erosion is proposed to be the most significant contribution to entrainment.