| Southeastern Tibet is located in the dynamic collision between Indian plate and Eurasian plate,which has a vast number of regional deep fractures,with this complicated geological environment,it is severely suffered from the mountain hazards and had an inestimable life and economic losses in the history,therefore,it has a great scientific significance and engineering values to study the influence of geological tectonic on debris flow of Southeastern Tibet.There are little research on the debris flow in arid areas of Southeastern Tibet currently,therefore,we choose the Lengqu arid valley as a case in this paper,First,the 37 debris flows in study area were investigated in the field,the engineering geological environment background of debris flow was identified by field investigate,remote sensing and GIS.Second,the disaster environment of study area was analyzed form earths androgenic and exogamic geological by comparing to other arid valley of China.Third,the distribution,formation,density,scale and frequency characters of debris flow was identified by field investigate,remote sensing and GIS on the basis of disaster environment.Then,the influence of debris flow characters from the stratigraphic lithology,basin morphology,geological structure,regional climate and other factors were analyzed by superposition and regression.Finally,a typical debris flow was chosen as a case to analyze the influence factors of debris flow characters deeply,and then,the development trend of typical debris flow was analyzed based on the above conclusion.The conclusion showing as following,(1)The disasters environment of debris flow in Lengqu arid valley was cleared.The earths androgenic and exogamic geological of Lengqu area are complicated and changeable.On the androgenic geological hand,Lengqu arid valley is located in the dynamic collision between Indian plate and Eurasian plate,which has a vast number of regional deep fractures,the nontectonic movement currently is around 20mm/yr,with a vertical divergence around 2.4mm/yr to 3.4 mm/yr,seismic activity are frequently,the seismic intensity is up to ? degree.The Basu Fault,Ritu-Gaize Fault and Namucuo-Zhongsha Fault are cross over the whole valley,and the Indosinian,Yanshanian and Himalayan volcanic rocks are developed accompanied with more than 40 faults in study area.There are three landform types in the valley,which are mountain stripped hilly landforms,alpine deep canyon landforms and glacier landforms.This lead to the maximum height difference of valley is up to 3243 m,the river drop is up to 29 ‰,the area of steep slope(slope> 25 °)is up to 61.17% of valley.On the exogamic geological hand,the annual precipitation of Lengqu is only 254.5mm,the dry and wet season is clear,the spatial and temporal distribution of rainfall is uneven,and the time of rainfall is mainly concentrated in the period from June to September.In the space,the high altitude area in the southwest of the valley is much larger than northeast low elevation area.The valley area is scarce vegetation,mainly meadow,shrub and coniferous forest,human activities are frequent,soil erosion is serious,the above androgenic and exogamic geological conditions of Lengqu area are conductive to development the debris flow.The results can provide a basis for regional prediction and prevention for debris flow.(2)The formation and movement characters of debris flow were identified.(1)There are 37 debris flow in the Lengqu arid valley.(2)The area of debris flow is mainly around 0.5~10km2,the basin form is mainly composed of birch leaves and the slope of the debris basin is between 25 ° and 55 °.(3)the source of debris flow is rich and complex causes,it mainly caused by collective effect of regional freezing cold weathering,freezing and thawing,earthquake,structural fissure transformation,runoff erosion and glaciation,dry and wet cycle.Water supply is mainly provided by rain,ice and snow melt water and GLOF.(4)The type of debris flow is mainly diluted debris flow,the density of debris is between 1.5 to 1.78 t/m3.(5)The scale of debris flow is mainly huge and large scale.(6)The frequency of debris flow is mainly high frequency.(3)The influencing factors and degree of debris flow characteristics are determined.(1)The source of debris flow are influenced by hill slope and stratigraphic lithology,the most source are come from the Jurassic and Cretaceous strata,sandstone,slate and diorite,and hill of slope between 20°to 30°.(2)The distribution of debris flow was mainly affected and controlled by fault.(3)The density of debris flow was influenced by form of watershed and stratigraphic lithology.(4)The frequency of debris flow was mainly influenced by drought climate change of region.(4)The evaluation index and statistical model of fault,which influence the scale of debris flow,were set up.The index of Accumulation of per unit area,which is used to evaluate the scale of debris flow,was put up and the index of Fault length of per unit area,which is used to evaluate the fault,was put up.By regression analysis of APUA and FLPUA,the result show that,the accumulation rate of the debris flow was increase because of the increase of the length of the fault per unit area in the basin,that's means the fault can influence the scale of debris flow,and large scale of debris accompany by more faults.The results can provide the value of geologic tectonic factor for the study of debris flow susceptibility,risk,risk assessment,prediction,and prevention and so on.Moreover,results can guide the prediction of the scale of debris flow in other areas.(5)The type and mainly influence factor of debris flow were determined.The type of debris flow in Lengqu arid valley is Rainfall control.In the development of debris flow,the fault is controlling factor for debris flow,at present,the source of debris flow is rich,therefore,the arid climate of regional is controlling factor.(6)The characters,influence factors and trend of development of Sengezong debris flow were analyzed.(1)Sengezong debris flow is an ancient debris flow,and it was break out the large scale of viscous debris flow in the history.Sengezong debris flow is low frequency debris flow now,it disasters has a periodicity,the outbreak period of dilute debris flow is about 10 to 12 years,the outbreak period of viscous debris flow is around 10 to 50 years.(2)Sengezong debris flow is in a transitional period of adolescence to recession currently,therefore,it may outbreak the dilute debris flow or flood,it is difficult to outbreak the viscous debris flow.The results can provide reference for the monitoring and early warning of the debris flow prevention. |
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