Analysis Of Hillslope Erosion Based On Threshold Hillslope In The Transverse Mountain Area

In recent years,studies on the evolution of the orogenic belt have focused on the coupling of glaciers,river erosion,and structural uplift.However,hillslope erosion as an important earth surface process also plays an irreplaceable role in the formation and evolution of the landscape.Especially in the deep canyon area,the erosion process dominated by landslides controls the direction and process of landscape evolution.Hillslope angle is an important indicator of hillslope stability.When the stable threshold hillslope is exceeded,the erosion rate of the hillslope will increase significantly and quickly adjust itself in the form of landslides.The research area of this thesis is the Transverse mountain area,where there are many high mountains and deep valleys.Landslides and other geological disasters occur frequently and there are many geological data.Various statistical methods were used in this thesis to obtain the range of the threshold hillslope of the Transverse mountain area.We then systematically analyzed the indicator function of the topography index“excess topography”based on the threshold hillslope theory in the research of hillslope erosion process.Based on the above research,the important role of hillslope erosion in landscape evolution is discussed.The main conclusions and understandings are as follows:(1)The average slope of the six major river basins in the Transverse mountain area is between 25°and 30°,and the area with a slope of 30±5°near the river valley accounts for up to 82%.Despite obvious regional differences in lithology,rainfall,and seismic conditions,the slope frequency distribution is very similar,with the frequency of 30±5°being the highest.Therefore,30±5°is a reasonable range of threshold hillslope in the Transverse mountain area.(2)The amount of excess topography is inversely proportional to the value of the threshold hillslope,but no matter how the threshold hillslope changes,the spatial distribution of the excess topography will not change,mainly distributed along the river channel,and all peaks are obtained inside the deep canyon.Taking 30°as an example threshold hillslope,the average thickness of the excess topography in the Transverse mountain area reaches 32.2m,which can supply at least 67,000 years of erosion materials.The Min River,the middle and lower reaches of the Dadu River and the Parallel River have a large distribution of excess topography,indicating that these areas have strong hillslope erosion capacity.(3)About 71% of the 4,430 landslides in the Transverse mountain area are located where the excess topography is distributed,and more than 48%are located in the excess topography with a height of more than 50m.Therefore,the surplus terrain not only represents potentially unstable mountains,but can also be used to indicate landslides which have occurred.The amount of excess topography in the six basin of the Transverse mountain area showed a strong linear correlation with the erosion rate measured by the cosmogenic nuclides burial ¹⁰Be,indicating that the erosion in the Transverse mountain area is largely provided by the hillslope materials and the distribution of the excess topography can be used to reflect the spatial differences in erosion capacity.The correlation between the excess topography in the Transverse mountain area and6)₉)is only reflected in some areas with small local relief indicating that slope erosion in the Transverse mountain area is not only a passive process in response to river erosion,but also an active erosion unit.(4)Erosion events such as landslides are extreme geological hazards.By adjusting the shape of hillslopes,basins,and longitudinal profile of rivers,impacting river sediment flux,hillslope erosion rapidly destroys the equilibrium state of landscape and profoundly changes the evolution direction and process of landscapes in the Transverse mountain area.The disturbance of hillslope erosion to normal landscape evolution can last for 10⁰-10⁴ years.It is a key link and research object connecting short-scale and long-scale landscape processes,and should be given full attention.(5)The spatial distribution of excess topography can provide a breakthrough for the understanding of the plateau uplift mechanism and hillslope erosion process.Because of its unique ability to indicate hillslope erosion and terrain stability,it can be applied in engineering construction and disaster prevention and reduction.