Preliminary reports of a catastrophic landslide occurred on August 21, 2020, in Hanyuan County, Sichuan Province, China
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Kun He I Bo Liu I Xiewen Hu
Preliminary reports of a catastrophic landslide occurred on August 21, 2020, in Hanyuan County, Sichuan Province, China Introduction After continuous two rounds of torrential downpours from August 10, 2020, a catastrophic landslide occurred in Hanyuan County, Sichuan Province, southwestern China (N 29° 20′ 26.74″, E 102° 41′ 51.30″) (Fig. 1) at approximately 03: 50 am, on August 21, 2020. Due to the long-runout of a large volume of loose materials, the settlement areas along the landslide sliding path were completely buried and the Provincial road S435 was blocked. The disastrous landslide has caused 9 fatalities and 8 houses destroyed. Immediately after this event, the Ministry of Emergency Management of the People’s Republic of China launched on-site emergency rescue and disaster mitigation operations. The landslide area has a length along the sliding direction of about 880 m, a width of about 280 m and a depth of about 20 m. The landslide area was estimated to be about 24.6 × 104 m2, and its
volume was about 500 × 104 m3. In addition, several tension cracks are seen atop the main scarp, which indicates that there are still signs of instability. Geological and morphological setting The Zhonghaicun landslide is located in the Alpine valley area of Dadu River Basin, with the landscape of deeply incised valleys and high mountains. The study area has a low to middle elevation mountainous topography, and the elevation difference between the ridge top and riverbed is approximately 185 m. According to the 1:500,000 geological map (Geological Survey Institute of Sichuan Province 1978), the exposed strata in the landslide area includes Triassic Xujiahe Formation (T3x). The bedrock lithology is mainly the highly weathered sandstone intercalated by mudstone, and the slope surface contains a thin layer of soil.
Fig. 1 The location of Zhonghaicun landslide in Sichuan Province, Southwestern China (E102° 41′ 51″, N29° 20′ 26″), (After Google earth, 2020)
Landslides
Landslide News Characteristics of the landslide Unmanned aerial vehicle (UAV) surveys combined with field investigations were conducted to characterize the landslide. The high-resolution orthophotographs and digital elevation model (DEM) for the entire landslide area have been obtained by using DJI Phantom 4 Pro UAV (Fig. 2). The survey results showed that the Zhonghaicun landslide originated at the hill peak of slope at about 1130 m in elevation; the landslide toe had an elevation of about 945 m, and the runout distance was 880 m. The pre-event DEM shows that the original slope has a step-like terrain and the crown area is steep with an average slope of 40°. Based on the landform expression and geologic material, the landslide area could be divided into three zones: initial sliding zone I, progressive sliding zone II, and fluidization zone III. Tremendous energy was released during the landslide runout, as it caused horrendous damage. As shown in Fig. 3, the agitating landslide masses with
tremendous kinetic energy damaged houses at