The Mechanism Of Disasters Induced By Coupling Of Endogenic And Exogenic Geological Processes In The Yarlung Zangbo River From Gongga County To Jiacha County

The coupling of strong uplift and exogenic geological processes of the Qinghai Tibet Plateau has formed a unique geological environment in the middle reaches of the Yarlung Zangbo River:high terrain difference,high fractured rock mass,intense freeze-thaw and glacial activity,etc.,which determines that this region is prone to natural disasters and rich in water energy and tourism resources,so disaster prevention and mitigation become an important issue.On the basis of previous research data and the investigation of the collapse,landslide,debris flow and sandstorm,the development law and formation mechanism of collapse,landslide,debris flow and sandstorm disasters in this study area are analyzed by using remote sensing interpretation,Arc GIS spatial analysis method,discontinuous deformation analysis method(DDA)and differential in synthetic aperture radar technique(D-In SAR).The main results and conclusions are as follows:(1)The collision between Indian plate and Eurasian plate occurred in the late Cretaceous and the inherited land convergence are the main internal driving forces for the formation of geological environment of Qinghai Tibet Plateau.Under the action of the above,the Qinghai Tibet Plateau rises rapidly,blocking the westerly jet and warm and wet water vapor from the Indian Ocean,changing the atmospheric circulation,and forming a modern East Asian monsoon climate,that is,dry and cold in winter,rainfall mainly concentrates in summer.There are spatial differences in the uplift strength of structures.The uplift of the fault block between Sangzhuling and Zangmu is the strongest,and the river erosion is high,forming a canyon area.The tectonic uplifting in the upstream and downstream areas is weak,and the river lateral erosion is strong,forming wide valley areas.(2)A total of 139 collapse disasters are developed,and the formation mechanism is as follows:high and steep terrain-high ground stress unloading,structural relaxation and fragmentation,freeze-thaw weathering-earthquake,rainfall triggering.The main deformation and instability mode is slip type,mostly concentrated in the Sangzhuling-Zangmu Gorge,and the development scale is mainly small.The distance from the fault zone(x)and collapse quantity(y)satisfy the relationship of y=-23.3049+61.8062·e^-0.1031x,the relative elevation range of 100-600m from the slope toe is the prone area of collapse disaster.(3)There are 94 landslides in total,and the formation mechanism is as follows:high and steep terrain-structural relaxation and fragmentation,freeze-thaw weathering-earthquake,rainfall triggering;the main deformation and instability mode is slip-crack type,which is most developed in Gongga-Sangzhuling wide valley area,accounting for64.89%of the total landslides,and the development scale is mainly small.With the increase of landslide scale(x),the number of landslides(y)decreases exponentially with=1.83+52.56·0)^-0.54.With the increase of the distance(x)from the back edge of landslide to the riverbed,the number of landslides(y)decreases exponentially with=0.2350+9.8689·0)^-0.0011(x>300).Within the elevation range less than200m from the toe of the slope,it is the prone area of landslide disaster.(4)There are 335 debris flow disasters in total,and the formation mechanism is as follows:three sides nestling among the hills-structure relaxation and fragmentation,freeze-thaw weathering-rainfall,ice and snow melt induced.The largest number of debris flow disasters developed in Gongga-sangzhuling wide valley,accounting for79.4%of the total.Under the influence of crustal uplift and river undercutting,with the increase of drainage area(x),the number of debris flow(y)decreases exponentially with=1.2352+32.4582·0)^-0.1021(>2).The relative height difference of debris flow is mainly concentrated in 700-1600m,the vertical slope is mainly concentrated in 110‰-270‰,and the length is mainly concentrated in 1800-6300m.(5)There are 256 rock glaciers in the study area,with a total area of 113.49 km².They are mainly developed on the west and northwest slopes of the high-altitude areas of Sangzhuling-Zangmu gorge,and the main development type is moraine rock glaciers.The formation mechanism of rock glacier-debris flow can be summarized as four processes:erosion recharge-transportation and deposition-runoff erosion-unstable flow.There are two types of rock glacier-landslides:one is the clastic sliding caused by the decrease of the natural repose angle under the effect of climate warming,the formation mechanism can be summarized as follows:temperature rising-ice core melting-natural repose angle decrease-sliding;the other is the rupture-collapse landslide induced by earthquake.(6)Local sandstorm disasters are formed by the uplifting of dry and loose sand on the surface of central bars and flood plains under the action of strong river valley wind.And the lifted sand is deposited on the valley bottom and bank slope to form aeolian sand after being blocked by the river valley bank slope and the surface friction.The formation process can be summarized as follows:river sand transport-sand exposed-strong wind uplift sand-sand deposition.Under the combined action of mountain valley wind,glacial wind and westerly jet in the valley,aeolian sand is mainly deposited on the bottom and bank slope of the left bank of Gongga-sangzhuling wide valley,and its formation time is mainly concentrated in the afternoon to night in winter and spring.There are 113 aeolian sand units,with a total area of 117.89 km²(2019).With the increase of unit area(x),the number of aeolian sand units(y)decreases with a power function of y=2.7249·x^-1.9248.Influenced by the natural repose angle of aeolian sand particles and the perennial microclimate of the valley,the slope of aeolian sand is mainly concentrated between 64°and 84°and the aspect is mainly concentrated between 90°and 225°.