Mass movement and formation process analysis of the two sequential landslide dam events in Jinsha River, Southwest China

Abstract

The formation of the landslide dam is believed to be case-specific and closely related to the dynamics of failure mass movement and river bed topography. This study focuses on two massive landslides, which blocked the Jinsha River twice on October 11 and November 3, 2018, respectively. The unique feature of these two sequential events was that the remnant of the 1st landslide dam body after break had a significant influence on the formation and shape of the 2nd landslide dam. Multiple methods were used to investigate landslides triggering factors and formation mechanism of these two landslide dams, including traditional field investigation, satellite remote sensing, and unmanned aerial vehicle (UAV) 3D image technology. After long-term creeping deformation under gravitational and hydrological effects, the first failure eventually occurred due to the short-term heavy rainfall in early October 2018. With a high speed along the steep slide bed, the failure mass of the 1st landslide rushed towards the opposite (left) bank of the Jinsha River, while the failure mass of 2nd landslide mainly accumulated at the toe of the slope (right bank) as a result of obstruction from the remaining body of the 1st landslide dam after overflowing. Another important observation is the scraping and entrainment effect on the 2nd landslide; consequently, the volume of the failure mass, which was about 2.0 × 106 m3 at source area based on UAV data, increased significantly to more than 6.0 × 106 m3. This substantially enlarged the volume of the new landslide dam with an unexpected height; thus, overflowing was not possible without manual excavation. An additional investigation implies that the Baige remnant slope is likely to fail again with considerable failure mass. These analyses presented in the paper indicate that multiple occurrences of landslides can significantly increase the risks associated with the compound landslide dams, considering also the volume amplification effect. Thus, timely measures should be carried out to reduce the unexpected devastating consequences prior to possible re-occurrence of landslide.