## 4 Results and Discussion  
### Landslide Inventory  
Landslides in the study area primarily lie along the northwest and southeast direction. There are two types of landslides in the region: slides and falls. About 15 observed landslides belong to slides and 12 falls. The amount of erosion is 704 \(\times\) 10\({}^{4}\) m\({}^{3}\) and 14.4 \(\times\) 10\({}^{4}\) m\({}^{3}\), accounting for 98% and 2% of the total landslide, respectively. The slide is the main type of landslide in the region, which had an important contribution to the frequency of landslide and the total amount of slope movements in the region. The triggering mechanism of falls is different from that of slides. When the water in the guilty scours and transports the lower accumulation, and the gravity moment generated by the upper steep wall under the action of gravity is greater than the tensile force moment of the soil, the upper soil layer loses its balance to fall [27]. There were many small falls in the study area. Most of the fall-bodies fell and broke, which were difficult to preserve for a long time. Most of them have been transported to form sand production, which is difficult to investigate [28].  
The volume of the smallest landslide is approximately 0.2 \(\times\) 10\({}^{4}\) m\({}^{3}\), the largest is around 270 \(\times\) 10\({}^{4}\) m\({}^{3}\), and the average is estimated to be 26.6 \(\times\) 10\({}^{4}\) m\({}^{3}\). Figure 3 showed the amount and frequency of landslides in each interval, which were tiny, small, medium, and large landslides. The total amount of erosion caused by large landslides of \(\geq\)100 \(\times\) 10\({}^{4}\) m\({}^{3}\) was the largest, which was 503.6 \(\times\) 10\({}^{4}\) m\({}^{3}\), accounting for 70.2% of the total erosion and followed by the erosion of the medium landslide, which was 174.7 \(\times\) 10\({}^{4}\) m\({}^{3}\), accounting for 24.4% of total erosion. The small landslide was 37.1 \(\times\) 10\({}^{4}\) m\({}^{3}\), accounting for 5.2% of total erosion, and the tiny landslide had the least landslide, at 2.7 \(\times\) 10\({}^{4}\) m\({}^{3}\), accounting for 0.2% of total erosion. In the case of frequency of landslides, there were 19 small-scale erosions with a volume of fewer than 10 \(\times\) 10\({}^{4}\) m\({}^{3}\) in the study area, accounting for 70% of the total frequency of erosion, that is, the occurrence of tiny-scale and small-scale landslides were higher in the area. While the amount of medium-sized and large-scale collapse accounted for 94.6% of the total, their frequencies of occurrence were only 5 and 3 times, accounting for 19% and 11% of the total frequency, respectively. It can be seen that the number of tiny-small landslides in the study area was more frequent. The frequency of medium and large-scale landslides was little, but they had a major contribution to the total amount of landslides. It can also be seen from the statistics that the contribution of frequency and the volume of landslides are not the same, and it is more meaningful to consider both effects in the study. The cumulative amount of landslide erosion in the study area reached \(718.1\times 10^{4}\) m\({}^{3}\). A large amount of landslide erosion has an important impact on sediment yield and sediment transport in the basin. The landslide-triggered erosion enters the channel and then flows into the river system by runoff, directly or indirectly transporting a large amount of sediment to the channel, which is one of the main processes of soil erosion and river sediment sources. Large slides also cause road damage and soil erosion. The volume of the falls is not large but their migration speed is fast. Because the occurrence to stop movement does not exceed 1 min, people are often unable to hide and suffer the risk of casualties; the harm is no less than the landslide. Between 1980 and 2015, there were 53 landslides over the Loess Plateau, killing and missing 717 people [29].