| In this paper,the study area is the Yarlung Zangbo River large bend east structural structure,under the plate compression tectonic background,the regional tectonic activity is strong,alpine canyon,valley plain,plateau and other geomorphologic units have developed distribution.Different geomorphological units develop different broad and narrow valleys and vertical landforms.The Yarlung Zangbo River flows from west to east through the eastern structure of the Indian plate and the Eurasian plate,and the river turns south to 90 °to form a large bend.In order to understand the development regularity and genetic characteristics of the large bend topography and landform of Yarlung Zangbo River,this paper is based on field survey data,numerical elevation data(ASTER-DEM)and Hypsometry Index.Combined with the structure,climate,lithology and other geological data for analysis and research.ASTER-DEM was used to extract many geomorphologic factors,including elevation,slope direction,slope and river profile,and the survey data included terrace,shoulder,inflection point,planation plane and disaster.Area-elevation integral transforms the qualitative features of regional landforms into quantitative features.The main results are as follows:(1)The formation of complex geomorphological characteristics in the region of the large bend tectonic junction is mainly influenced by the interaction of structure and climate.Seven geomorphologic units are mainly developed in the land,including the mountainous area in the middle reaches of the Yarlung Zangbo River,the extremely high mountain areas strongly cut by the Yarlung Zangbo River,the middle reaches of the Yarlung Zangbo River cutting high mountains,and the lower reaches of the Yarlung Zangbo River strongly cutting Zhongshan.The Sanjiang basin cut the extremely high mountain area intensively,and the Parong Zangbu cut the high mountain area strongly.(2)based on the ASTER-DEM data,the area elevation integral(HI)value of the study area is calculated by ArcGIS.The results show that the structure and climate are the main factors affecting the HI value of the region.The value of HI increased gradually from outside to inside at the turn of the Yarlung Zangbo River and the outlet of the Nyang River,and the uplift increased gradually.In the area dominated by tectonic action,the HI value is higher,HI ? 0.43,is in slow uplift,even strong uplift,the landform is dominated by high mountain canyons,and when climate action is the main area,HI < 0.43,uplift stagnation or erosion levelling,The area is centered around Nanjiabawa and Galabel peaks and is located in the Alpine Valley plain or Pingba area with a low HI value.Lithology has little effect on HI value.The Yarlung Zangbo River,as the transportation channel of warm and wet airflow in the Indian Ocean,makes the climate erode the region more and more.(3)based on ASTER-DEM data,ArcGIS was used to extract the longitudinal section,width,slope direction and slope of the valley in the study area.(1)The main rivers,such as Yarlung Zangbo River,Parong Zangbu and Yigongzangbu,developed the zaggy crack point,the straight white crack point,the zaggy to the straight big bend crack point,the tributary Yigong township,the ancient township and the Tongmai rift point.The zhaququ and Tongmai rifts are formed on the basis of tectonic action,and the rift points of Zhibai,Yigong and ancient townships are related to the climatic action,and the large bend rifts from Zhibai to Zagqu are controlled by the mutual action of structure and climate.(2)The river flow direction in the study area is more east-west direction than that in the north-south direction,then the slope direction is mainly southnorth direction;(3)The river width is coupled with the longitudinal section of the river,and the tectonic action is the main area.the river develops canyons,the longitudinal ratio drop is large,the valley width is small,and the erosion deposition is strong and the longitudinal ratio drop is small in the river section with the main climate action.The width of the river increases;(4)Because of the complexity of geomorphology,the slope size distribution in the region is different.in the tectonic active area,the extremely high mountain and canyon landforms are developed,the slope is on the high side,the slope is small on both sides of the valley bottom,and the slope is on the small side in the mountain plain and valley plain.The erosion layered landforms of valley shoulder and peeling surface are developed on both sides of the valley,and the slope of the distribution of layered landforms is less than that of rapid downward cutting.(5)The longitudinal section of the river is mainly in the young deep section under the tectonic action,and when affected by the climate,it is mainly in the old age equilibrium stage.(4)Regional geology and climate have strong control over geological environment.(1)Glaciers,landslides or debris flows form dammed lakes and gradually form valleys and lacustrine facies deposits;glaciers carry a large amount of moraine into gullies,and a great deal of moraine is carried into gullies during glacier activities,and the river valleys and lacustrine facies deposits are gradually formed.It is deposited on both sides of the river valley and inside the river bed;the broad valley section of the Yarlung Zangbo River is consistent with the regional westerly wind,which causes the accumulation of aeolian deposits on both sides of the strait;and the river sediments are distributed on the riverbed and on both sides of the river,mainly in the form of flood flats and terraces.Most developed broad valleys and broad narrow valleys transition;(2)A large number of geological hazards,such as landslide and debris flow,were developed in the river reach of the study area,in which the landslide mainly distributed in the canyon section of the river,which was mainly controlled by the factors such as structure,climate,landform and earthquake;(3)The regional development of alpine valley plain and alpine valley flat dam geomorphology,the development of deep overburden in the unit geomorphology,the thickness of sediment cover in the wide valley section of the main stream of Yarlung Zangbo River is large,the maximum is more than 600 m;(4)Under the dynamic action inside and outside the region,rainstorm debris flow,glacier debris flow and glacier-rainstorm debris flow are developed,mainly rainstorm debris flow,mainly distributed in alpine valley plain and valley flat dam.A few glacier debris flow or glacier rainstorm debris flow development and canyon section. |
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