Catastrophic landslide triggered by extreme rainfall in Chongqing, China: July 13, 2020, Niuerwan landslide

Extreme rainfall events have become an increasing component of the annual precipitation in China, which caused amounts of geological disasters, especially in Southwest China. At approximately 7 a.m. (Beijing time) on July 13, 2020, a catastrophic soil and rock landslide occurred in Baima Town, Wulong District, Chongqing, China. With a length of 750 m and a width of 125 m to 260 m, the landslide carried approximately 1.4 × 106 m3 of rock and soil debris and destroyed eight houses, two main roads, a shale gas pipeline, and a large amount of farmland. After the landslide failure, the accumulation zone still deformed responding to continuous rainfall. The failure mechanism of the landslide was analyzed based on the geological conditions, deformation process, and triggering factors. The research shows that the Niuerwan landslide had a complex deformation process. According to the deformation characteristics, the landslide is divided into five parts: the source area, the compression area, the rapid-sliding area, the landslide-affected zone, and the accumulation area. The source area was triggered by continuous torrential rainfall and controlled by mudstone and bedding plane. The variation of the microrelief in the study area has a significant effect on the failure model of the landslide. Precipitation triggered the failure of the steep source area which impacted the middle part. Eventually, a continuous sliding surface developed along with the weak layer, giving rise to catastrophic failure. Moreover, the accumulation area at the steep slope toe rapidly moved downward to form a debris flow under the combined action of the geological conditions and rainfall. The Niuerwan landslide is a complex rainfall-induced landslide with a unique evolution process, which can provide some useful information for the early warning and deformation mechanism of landslides in similar geological settings.