## 4 Results
### Identification and Preliminary Validation of GALs in Lengqu River Section Based on RRIM
In visual  
Figure 3: Flow chart of RRIM synthesis in Lengqu River section (firstly, the DEM with 12.5 m spatial resolution is obtained to extract ground slope, topographic positive openness and topographic negative openness, and then the slope is rendered in red, the topographic positive openness and topographic negative openness are synthesized into ridge and valley index, and, finally, red slope and ridge and valley index are synthesized into RRIM map). interpretation, the RRIM method is obviously better than the original DEM and hillshade transformation. Compared with SVF, its advantages mainly lie in the visual effect brought by the color transformation, which makes the landslide and the surrounding non-landslide landscapes better distinguished and the deposition and landslide wall more detailed so that the specific structural composition of the landslide can be better seen. The results of the interpretation of GALs based on the RRIM in the Lengqu River section are compared with those in Google Earth through remote sensing image interpretation and fieldwork. Figure 4 shows four typical GALs in the Lengqu River section by field investigation, which are the Linka landslide, Basu landslide, Wangbi landslide and Duolashenshan landslide from top to bottom, and their surface areas are 6.102 km\({}^{2}\), 13.348 km\({}^{2}\), 2.060 km\({}^{2}\) and 0.961 km\({}^{2}\), respectively. Among them, the fourth and fifth columns are the four landslides identified based on the RRIM and Google Earth, respectively. It can also be found that the landslides identified by RRIM transformation are more detailed and distinctive than those identified by Google Earth, and the RRIM makes the location of landslide occurrences more prominent by weakening the irrelevant information around the landslides. In a word, the reliability of the identified landslides by the RRIM method is high. Figure 4: Typical GALs identified by RRIM in Lengqu River section. Quantitative Analysis of the Relationship between GALs and Excess Topography in Lengqu River Section  
Excess topography is an indication of potential slope above a certain threshold hillslope, that is, the slope above the excess topography is at risk of landslides; therefore, quantitative analysis of excess topography at the location of GALs, resurgent GALs and the deposition of inactive GALs can provide a basis for whether new landslides or resurgent GALs are prone to occur at the original location of GALs and avoid risk to a certain extent. For the quantitative analysis of landslides on excess topography, [PERSON] et al. considered landslides as point data, [PERSON] et al. considered landslides as surface data, and this research used landslide surface data for relative analysis considering the small area of the Lengqu River section. Based on 12.5 m DEM data, the slope of the Lengqu River section is extracted; as shown in Figure 6a, the plurality of slope in the Lengqu River section is 30\({}^{\circ}\), and the mean value of its slope was found to be 26\({}^{\circ}\). The Lengqu River section was then divided into 14 sub-basins according to the 10-level basin in the HydroBASINS 12-level basin dataset (as shown by the sub-watershed boundary in Figure 1), and the plurality value of slope in each sub-basin was extracted. As shown in Figure 6b-o, the slope plurality values of the 14 sub-basins are 23\({}^{\circ}\), 23\({}^{\circ}\), 23\({}^{\circ}\), 4\({}^{\circ}\), 30\({}^{\circ}\), 30\({}^{\circ}\), 30\({}^{\circ}\), 30\({}^{\circ}\), 23\({}^{\circ}\), 30\({}^{\circ}\), 30\({}^{\circ}\), 30\({}^{\circ}\) and 34\({}^{\circ}\), and these results are summarized in detail in Table 2. The slope plurality value of the fourth sub-basin is 4\({}^{\circ}\), but it can be found that there is no distribution of GALs, so the slope plurality value of this basin is not considered. Based on the analysis of Figure 6, the threshold hillslope of the Lengqu River section is about 20-35\({}^{\circ}\).