Insights into the long-term stability of landslide dams on the eastern margin of the Tibetan Plateau, China-A case study of the Diexi area

Landslide dams, especially long-term stable landslide dams, have been recognized as important contributors to regional geomorphological evolution. Here, the Diexi area, a long-term stable dam-prone area located in upstream of the Minjiang River on the eastern Tibetan Plateau, was adopted to reveal reasons that landslide dams are concentrated in this area and maintain long-term stability via detailed field investigations, landslide dam sampling, unmanned aerial vehicle (UAV) images, and digital surface models (DSM). The results show the controlling factors that the slopes are prone to sliding and rock mass structure deterioration including lithological combination mode, slope structure, topographic conditions, a series of NNE-trending radial fissures and hydrological conditions. Fault activities, which have caused many earthquakes, are the main inducing factor. Landslide dams are prone to occurrence in the Diexi area owing to the combined effect of the narrow channels, the large landslide dam volume and the rock fragments. The river flow, and the landslide dam volume, material, structure, and parameters control the stability of landslide dams. The landslide dam consists of various sizes of boulders and all landslide dams exhibit an obvious inverse grading sequence, and this size combination could consume most of the flow energy, and consequently protect the dam from incision. Additionally, a total of seven knickpoints were formed by landslide dams, and the longitudinal gradient upstream of every landslide dam was found to decrease by the action of knickpoint. In the eastern margin of the Tibetan Plateau, there are numerous landslide dams existed for hundreds or thousands of years. Studies on the long-term stable landslide dams in the Diexi area could provide experience for studying similar kinds of landslide dams in this region.