In 1983, a catastrophic landslide occurred in Saleshan, Dongxiang, Gansu, China, which resulted in the death of 237 people and the destruction of 585 houses. Saleshan landslide was a typical rapid moving landslide in loess area, China, which moved with extremely high speed and long run-out distance on a gentle sliding surface. This paper reviews the characteristics of the landslide and its consequence, analyzes the possible triggers and the processes of development, and back-calculates the kinematic characteristics of the landslide. The digital elevation models (DEMs) of the study area before and after the event were used to analyze the geomorphological characteristics before and after the event. The authors inferred the possible deformation and failure processes of the landslide based on available observations. Direct shear tests were carried out to obtain the parameters of the soil involved in the failure and postfailure process, which was adopted in the following simulation using an energy-based runout model. The velocities of moving materials at a different time stage together with the variation of runout distance and maximum flow height are presented. The authors also compared the calculated results with field observations and previous simulation results. Sensitivity analysis was conducted to understand the effect of internal and basal friction angles on the kinematic characteristics. This study indicates that the Saleshan landslide was a fast-moving landslide with long traveling distance. The landslide lasted more than one minute with a maximum velocity of approximately 25 m/s according to the calculation using the energy runout model, which was consistent with the estimations based on the observation of eyewitness. This study also gives an insight on the progressive failure mechanism and explains the high mobility of Saleshan landslide in details, which provides a reference for hazard zonation for areas along loess platforms.

Introduction Landslides are an important process which posed significant hazards, resulting in fatalities, property damage and degrading farmland (Huang, 2009). From 2004 to 2010, 2620 fatal landslides were recorded, which resulted in a total of 32,222 recorded fatalities (Petley, 2012). In China, most of the landslides occurred in high-altitude regions such as Qinghai-Tibet plateau and southwest area in China (Huang, 2007). According to the statistical data provided by the Ministry of Land and Resources of the People’s Republic of China, landslide geohazards have caused 4,718 fatalities from 2004 to 2016 (Zhang and Huang, 2018). Every year, one-third of the geohazards in China occur on the Loess Plateau (Zhou et al., 2002), with more than 80% involving landslides with slip surfaces shallower than 10 m (Zhuang et al., 2017). The main types of landslides involving substantial amounts of loess include flow, fall and slide (Li et al., 2013; Hungr et al., 2014; Zhang et al., 2012). According to the field investigation, it was found that most of the landslides in the loess area occurred on a slope around 20º – ۳۵º and the flowslides had a long runout distance due to soil liquefaction resulting in a low frictional angle (Zhang et al., 2009; Zhang et al., 2013; Zhang et al., 2014). Since 1900, more than 20 catastrophic landslides have been recorded whose volumes are greater than 20  ۱۰۶ m 3 , several of which occurred in loess area of China (Derbyshire et al., 2000; Wen et al., 2004; Huang, 2007; Wang et al., 2014; Xu et al., 2014; Zhang et al., 2014; Zhang and Wang, 2018) (Table 1). The landslides triggered by Haiyuan Earthquake 1920, are typical examples of these cases which in total resulted in more than 100,000 deaths (Huang, 2007; Wang et al., 2014).