## 2 Study Area and Materials  
### Study Area  
The upper reaches of the Yellow River lie in the transition zone between China's first- and second-step topographies (Figure 1a). The abundance of water, and the great difference in the topography of the country, mean the water contains high levels of energy. The valley is mainly composed of hard rock masses, including granite and shallow metamorphic rock, with excellent geological engineering properties for dam construction [27]. As a result, more than 20 hydropower stations have been built in the region to meet China's dual carbon targets and the growing demand for electricity. The Laxiwa hydropower station is the second cascade power station between Longyang Gorge and Qingtong Gorge, located between Guide County and Guinan County in Qinghai, about 32 km from the outlet of the Longyang Gorge Reservoir (Figure 1). The height of the arch dam of the Laxiwa hydropower station is 250 m, the thickness of the dam top is 10 m, the maximum reservoir capacity is about 1 billion m\({}^{3}\), the total installed capacity is 4200 MW, and the maximum generation flow is 1900 m\({}^{3}\)/s. It has the largest installed capacity, the highest generation efficiency, and the largest generating capacity among the numerous hydropower stations in the upper reaches of the Yellow River. The dataset was provided by the National Cryosphere Desert Data Center ([[http://www.ncdc.ac.cn](http://www.ncdc.ac.cn)]([http://www.ncdc.ac.cn](http://www.ncdc.ac.cn)), access date: 10 August 2021).  
The Laxiwa hydropower station was constructed in 2001 and became operational in May 2009 [28]. The first impoundment was completed in March 2009, and the water level increased from 2250 to 2340 m ASL. At the end of May of the same year, the staff found that the Guobu slope had begun to undergo deformation again. The monitoring work began in August of the same year, and 17 GPS monitoring points were arranged on the top platform and surface of the slope; Figure 1e shows their distribution [29]. After an evaluation study was undertaken by relevant experts, the reservoir water level was allowed to rise gradually. Subsequently, the water level was successively raised to 2400 m, 2430 m, and 2448 m ASL in February 2010, February 2011, and September 2012, respectively. The water level remained stable at 2448 m ASL from September 2012 to May 2015, and  
Figure 1: (**a**) Location of Guobu slope in China. The green and yellow blocks indicate the Qinghai-Tibet Plateau and the Loess Plateau, respectively, and the green triangle and the five-pointed star indicate the study area and Beijing; (**b**) DEM of the study area; (**c**) Google Earth image of the study area in 2005; (**d**) Google Earth image of the study area in 2020; (**e**) GPS monitoring point distribution.  
then was allowed to rise to the designated level of 2452 m ASL at the end of October 2015, and it remained relatively stable after that [30]. Since the first impoundment, the river channels have widened from ~70 m to ~500 m (Figure 1c,d), causing three slopes, including the Guobu slope, to start to move [31]. From 2015 to 2018, two slopes about 4 km and 8 km upstream of the Laxiwa dam exhibited a moderate movement rate of 40-60 mm/y. However, the Guobu slope, showing larger and faster movement, and being situated only 1 km southwest of the Laxiwa hydropower station, has emerged as an imminent threat to the dam, its powerhouse, and the surrounding residential community approximately 4 km downstream, thereby drawing significant attention [30].