Mechanism of the 2019 Yahuokou landslide reactivation in Gansu, China and its causes
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Zelin Zhang
Mechanism of the 2019 Yahuokou landslide reactivation in Gansu, China and its causes
Abstract In this study, we investigated a recent landslide that occurred in Zhouqu County, China. At 18:00 pm Beijing time on July 19, 2019, the Yahuokou landslide was reactivated. About 3.92 × 106 m 3 of debris slumped from the slope, blocking the Minjiang River channel, causing the water level to rise, and disrupting road. Fortunately, there were no injuries. A field survey, remote sensing imaging, borehole core analysis, landslide monitoring, and rainfall data analysis were conducted to examine the geomorphologic and stratigraphic characteristics of the landslide, the reactivation causes, and the dynamic mechanism of the landslide. A model for the reactivation and evolution of the landslide is presented. The field survey of the sliding zone indicates that the landslide has a flow-slide deformation pattern. The landslide mechanism is summarized as follows. Initially, slow plastic flow sliding occurred in the upper sliding body. Then the platform in the middle gentle slope was preloaded by deposits from the upper part failure, resulting in a “cutting and filling” effect. The failure occurred in the form of creep–tension cracks–debris flow–slide. Finally, the block on the lower part slumped. Thus, the upper, middle, and lower parts of the landslide all transferred stress in the same manner, being activated step by step, and slowly slumped into the river. Keywords Yahuokou landslide . Zhouqu County . Slump . Flow slide Introduction Zhouqu County is located in southern Gansu Province, China, on the northeast edge of the uplifted Tibetan Plateau. The upper reaches of the Yangtze River in Zhouqu County are highly susceptible to landslides because of the topography, lithology, and tectonics of the area (Wang 2013; Wang et al. 2013; Xiao et al. 2013; Zhang et al. 2017). This area has one of the highest occurrence rates of geological disasters in Gansu Province and even nationwide. According to a 1993 survey, there were more than 100 landslides in Zhouqu County, including more than 25 disastrous landslides (Zhao 2004). The 2008 Wenchuan earthquake (Ms 8.0) and the 2010 Zhouqu debris flows caused serious loss of life and property in Zhouqu County (Bai et al. 2012; Sun et al. 2015; Zhang et al. 2018). Thousands of landslides were reactivated (Xie et al. 2017; Yuan et al. 2018), and the fragile geological environment in the area was destabilized; the earthquake and mudflows caused damage to the stratigraphic texture and increased the loose debris and deposits. Currently, Zhouqu County is surrounded by many potential landslide sites with a high risk of reactivation, such as the Suoertou landslide, Xieliupo landslide, and Jiangdingya landslide (Guo et al. 2019). At present, some of the landslides are slowly creeping, increasing the risk of future disasters.
At approximately 18:00 Beijing time on July 19, 2019, the dormant Yahuokou landslide, Zhouqu County, Gansu Province, China, was reactivated (Fig. 1), with a landslide volume o
