The evolution of the Samaoding paleolandslide river blocking event at the upstream reaches of the Jinsha River, Tibetan Plateau

Abstract

A large number of landslides have occurred in the upstream reaches of the Jinsha River, Tibetan Plateau due to the intensity of tectonic movement in the area. Remote sensing and field investigation indicate that one of them, the Samaoding paleolandslide, previously blocked the river. Various river-blocking phenomena are well preserved, including the old landslide dam and deposits, fluvial sediments, and hydrostatic sandy sediment. To better understand the evolution of the Samaoding landslide, the authors carried out thermoluminescence (TL) dating and numerical simulations. The TL analysis shows that the landslide occurred at 10.6 ± 0.5 Ka BP. Discrete element method (DEM) simulation of the landslide based on landform restoration provided results that are consistent with field observations. The simulation indicates that the entire landslide process lasted for 80 s, and the sliding mass reached a maximum velocity of 64 m/s. The landslide formed a landslide dam with a length of 1900 m, a width of 600 m, and a depth of 200 m. The simulation results show that the level of the riverbed at that the time of the landslide was at least 25 m higher than it is today. On the combined basis of the simulation results and field observations, the authors propose explanation that the following valley evolution sequence occurred after river blocking. The landslide dam experienced flood overtopping and then was eroded until it had mostly had been transported away by river flow, and the river then rapidly incised the bedrock to form the present-day landform. Based on the field investigations, the authors summarize the failure mechanism of steep-inclined antidip rockslides and found that tectonics play an important role in the formation of landslide dams (or trigger of landslides) and the failure of landslide dams in an active tectonic environment of Tibetan Plateau.