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 hazard survey engineering.

Objective The Yalong River Basin is an important base for forestry, animal husbandry, hydropower, energy, and minority communities in western China. It is of great significance to study the causes and distribution of landslides in the Yalong River Basin to formulate scientific disaster prevention and mitigation strategies and ensure stable economic and societal development.

Methods The Zituoxi–Malangcuo river section in a deeply incised valley area of the Yalong River Basin was used as the study area. Basic landslide data were obtained through high−resolution satellite remote sensing interpretation, InSAR analysis, and field investigation. The typical landslide types and their formation mechanisms were summarized and analyzed using an engineering geology analysis method, and the distribution regularity and dominant development range of landslides were revealed by means of GIS spatial analysis and statistical methods.

Results (1) A total of 606 landslides were identified in the study area, among which the number of landslides with an area of 10⁴−10⁵ square meters was the most, accounting for approximately 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 approximately 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 macroscopically concentrated along river valleys such as belts.

Conclusions The research results provide a significant scientific basis for understanding the causes and regularities of landslides in the deep incised valley of the Yalong River, and preventing and controlling the risk of geohazard chains in the river basin.