## 4 Results  
### Identification and Preliminary Validation of GALs in Lengqu River Section Based on RRIM  
The process of synthesizing RRIM 2D-visualized terrain for the Lengqu River section mainly includes the extraction of the ground slope, calculation of topographic positive and negative openness, calculation of the ridge and valley index, rendering of the red slope map and the synthesis of final RRIM. The synthesis of RRIM for the Lengqu River section is shown in Figure 3.  
Figure 4 shows the DEM, hillshade transformed from DEM and SVF obtained from DEM either through SAGA software in the first, second and third column of the image, respectively, in the Lengqu River section: from the morphology of landslides, the areas where landslides occurred have more obvious landslide phenomena, and their shapes are mostly fan-shaped, tongue-shaped, skip-shaped, etc. In addition, some landslides can be seen with obvious depositions; it is difficult to judge only from the DEM and hillshade by the color of the landslides, as the color contrast between the overall landslide areas and the non-landslide areas is not obvious enough. Therefore, we chose to use SVF to show the whole geomorphological situation at the same time [37]. It is obvious from the  
figure that SVF can see the details on the geomorphology better than the original DEM and hillshade and can show the outline of GALs more clearly; the color of black and white contrast is stronger, but the specific composition of the landslide such as deposition is still difficult to identify. From the topography around the landslide occurrences, it is found that GALs are mainly distributed along rivers. In a word, the DEM and hillshade portrayed landslide surfaces roughly, so it is easy to misjudge landslides; even some of the more subtle structures of the landslide are not visible through SVF. In order to be able to solve the problems encountered in the original DEM, hillshade and SVF methods for landslide identification, we introduce the RRIM method to the research. We identified GALs in the Lengqu River section based on an RRIM 2D-visualized topographic map with well-defined colors of valleys and ridges in Figure 5. A total of 54 GALs were identified based on the morphological features, color changes and changes in the topography around the landslides presented in the RRIM at last. The area range of the identified GALs is 0.036-13.348 km\({}^{2}\), and their minimum area includes 230 grids. In Figure 5, we can see that the central and southern ridgelines of the Lengqu River section are dense, as well as the topographic changes through the undulation of the surface morphology, with a strong sense of three-dimensionality and obvious visual impact. Based on the morphological characteristics of the landslides, the DEM with RRIM changes can clearly identify the entire contour, back edge, steep walls on both sides and depositions of GALs, and some can even portray the local subtle features of the landslides, such as landslide steps, etc. Especially for the relatively giant landslide, we can not only see the contour and depositions of landslides but also the rocks or debris materials sliding down along the landslide profiles or even the slip zones. For relatively small landslides, we can see landslide profiles and depositions but cannot see the material characteristics of the landslide surface slip. In terms of color, there are gray rocks exposed at the location of GAL occurrences, and the color of the surrounding terrain is more uniform, which shows a red color. From the topography around the landslide occurrences, there are obvious depressions and ruptures in the terrain where the landslide occurred.