Identification Old Landslides in Permafrost Degradation Area in Northeast China by Difference Distribution of Surface Trees

With the development of global warming, the permafrost in Northeast China, which is located in the south margin of permafrost area in Eurasia, has gradually degenerated, resulting in an increased incidence of landslides. At present, research on the occurrence mechanism, movement process characteristics and evolution trend of landslides in permafrost area, is limited and lacking in detail. It is difficult to identify landslides that have cured within the last hundred years as movements have been relatively small during this time period. In addition, the lack of written records, the unusual geological environment and landforms and the surface coverage, as well as the landslide mechanisms mean that accurate identification is difficult using existing technology. In this paper, Beian-Heihe expressway, which is located in the permafrost degradation area of Northeast China, is selected as the research area. Field investigation, 3D modeling of UAV image, high-density electrical survey, geological drilling and other methods are used to study the distribution of new and old landslides in the area. The study found that the distribution of tree populations at the boundary of the old landslide and some parts on the landslide body was significantly different from the distribution of tree populations outside the landslide body. In combination with tree core sampling, with the help of the relevant theories and methods of dendrochronology, Statistical analysis of tree species distribution and tree ring differences was used to estimate the occurrence time of old landslides. Combined with the previous research results, the relationship between the movement process of landslides and the degradation of permafrost in the study area is analyzed. This method can effectively realize the positioning and model reconstruction of old landslides in a short time scale, which will have important theoretical and practical significance for the early warning and treatment of landslides in permafrost degradation area.