Effect Of Permafrost Degradation On Geological Hazards In Northwestern Hengduan Mountain Area

Permafrost is one of the most important parts of the cryosphere.With the global warming,permafrost has been degraded by the increase of active layer,the increase of permafrost temperature,the partial disappearance of permafrost and the decrease of permafrost area.The degradation of permafrost will destroy the balance of the original regional system and affect the regional disaster environment,ecology and social production activities and so on.The degradation of permafrost will cause slope instability,and form a large number of ice lakes in alpine areas,which will lead to landslides,debris flows,ice lake outbursts and other disasters,endangering the sustainable development of the ecosystem around the mountain area and the safety of human production and life,as well as transportation,agricultural production and infrastructure in alpine areas.The northwest of Hengduan Mountain area is located in the southeast edge of Qinghai Tibet Plateau.There are high-altitude frozen soil in middle and low latitudes in the area.This area belongs to a typical alpine gorge area.The topography is broken and complex,and geological disasters occur frequently.With the continuous warming of the climate,the permafrost in the area is deteriorating,and the permafrost environment is constantly changed,which will further induce geological disasters and endanger the regional security development.In this paper,the elevation response model proposed by Cheng Guodong et al.Is used to simulate 7 periods of permafrost distribution data with spatial resolution of 1km in the study area in 1950s,1960s,1970s,1980s,1990s,2000s and 2010s.The existing permafrost data are used to verify the simulation results,and the temporal and spatial variation and degradation of permafrost are analyzed,Through further analysis of the influence of frozen soil degradation on geological disasters,the following conclusions are drawn:(1)Through the elevation response model,the simulation data of frozen soil distribution from 1950s to 2010s are obtained,and the results are verified,and it is found that the simulation results are reliable.From the distribution area of permafrost,the permafrost area from 1950s to 2010s is.2908×10~4km~2、5.2768×10~4km~2、5.2756×10~4km~2、5.2628×10~4km~2、5.261×10~4km~2、5.248×10~4km~2 and 5.2386×10~4km~2 respectively.With the climate warming in the study area,the distribution area of permafrost is deteriorating.(2)In terms of time and the total reduction of permafrost,the degradation area of degraded permafrost is in the order of 1950 s-1960s>1990s-2000s>1970s-1980s>2000s-2010s>1980s-1990s>1960s-1970s,and the most degradation area of permafrost is 0.0140×10~4km~2.The degraded part is mainly distributed in the transition zone between permafrost and seasonal frozen soil;From the perspective of spatial distribution of permafrost,"inherent permafrost area"is continuously distributed in the northwest and northeast of the study area,scattered and discontinuous in the central and southern regions“The"natural seasonal frozen soil area"in the study area gradually decreases from south to north,although it increases,but its spatial distribution changes slightly;The permafrost is decreasing in the adjacent years,and the permafrost decreasing area is mainly distributed in the transition zone between permafrost distribution area and seasonal permafrost distribution area;Except for 1990s-2000s and2000s-2010s,the permafrost increased slightly in the other adjacent years,and the"permafrost increasing area"was mainly distributed in Batang County.(3)Based on the gravity center transfer model,the spatial transfer of the gravity center of permafrost and the spatial transfer of the gravity center of geological disasters are studied.It is found that from 1950 s to 2010s,the gravity center of permafrost in the study area is 75°to the South and West,it moved 691.22m;On the other hand,the center of gravity of geological disasters is 83°to the North and East,the movement is259.37km,and the direction of frozen soil degradation is basically the same as that of geological disaster increase.By analyzing the spatial distribution of geological disasters in different permafrost regions,it is found that in addition to collapse,the number of various geological disasters in permafrost regions,island permafrost regions and seasonal permafrost regions is increasing;There are 1430,2044 and 3087 geological disasters in the three different permafrost regions.With the decrease of permafrost stability,the number of geological disasters is increasing.(4)Through correlation analysis,the distribution area of permafrost from 1950s to2010s is analyzed with the number of landslides,debris flows and collapses.It is found that the permafrost distribution area in each age has a significant negative correlation with the number of landslides,landslides and debris flows.The correlation coefficients are 0.828,0.860 and 0.836,that is,with the continuous decrease of permafrost distribution area,The number of geological disasters is increasing;From the perspective of spatial distribution,geological disasters gradually increase from south to north,from east to west,and the spatial direction of geological disasters is basically the same as that of permafrost.In addition,the study area is multi-ethnic agglomeration,high risk of disaster,so we should strengthen the management of permafrost degradation and geological disaster prevention and mitigation.