Type, formation mechanism and distribution regularity of landslides in the deeply-incised valley area of Yalong River basin——a case study of Zituoxi–Malangcuo river section

This paper is the result of geological hazards survey engineering. ObjectiveThe Yalong River basin is an important base of forestry and animal husbandry, hydropower and energy, and minority communities in the west of China. It is of great significance to study the causes and distribution of landslides in the Yalong River basin MethodsThe Zituoxi-Malangcuo river section in deeply-incised valley area of Yalong River basin was taken as the study area in this paper. The basic landslide data were obtained through high-resolution satellite remote sensing interpretation, InSAR analysis and field investigation; typical types of landslides and their formation mechanism were summarized and analyzed by engineering geology analysis method; the distribution regularity and dominant development range of landslides were revealed by means of GIS spatial analysis and statistical method. ResultsThe results showed that:(1) A total of 606 landslides were identified in the study area, among which the landslide with an area of 10⁴~10⁵ square meters was the most, accounting for about 60 percent of the total, and the number of landslides with areas of 10³~10⁴ and 10⁵~10⁶ square meters were essentially equal, accounting for about 20 percent of the total respectively; (2) Landslides were divided into five main types, i.e. rainfall-induced type, structure-controlled type, excavation-induced type, river erosion type and water impoundment-induced type, according to the main controlling factors of landslides. The key mechanism responsible for the occurrence of landslides mainly including the weakening effect of rock and soil strength by rainfall and impounded water, the deterioration effect of rock structures and its mechanical properties by fault structures, and the release effect of the anti-sliding and supporting action at the front of slope caused by excavation and river erosion; (3) The dominant terrain ranges for landslide development were of elevation 2500~3500 m, slope angle 15°~35°, and slope aspect NE~E and S~W; (4) The soft metamorphic rock group composed of thin-bedded slate and silty slate was the dominant lithological group for development of landslides, while landslides in the magmatic rock group consisted of hard intrusive rocks such as granite and quartz diorite was the least; (5) the Kangdu fault, Qianbeinima fault, Zhusang fault, Tanggang fault, Huozezhari fault and Nieda fault were found having less impact on the development of landslides, however, landslides developed densely at both sides of the Mazishi fault, Chengzhang fault, Rangong fault and Jida-Milong-Muhui fault and at zones where these faults intersected in the downstream of the study area; (6) A negative correlation between the distribution of landslides and the distance to the river systems can be obviously seen, and a distance to the river systems of 0~0.5 km was found to be the dominant distance range of landslide development. The landslides were concentrated along the river valleys like belts macroscopically. ConclusionsThe research results could provide a significant scientific basis for understanding the causes and regularities of landslides in the deep-incised valley of Yalong River as well as for preventing and controlling the risk of chain of geohazard in the river basin.