Study on the characteristics of huge scale-super highspeed-long distance landslide chain in Yigong,Tibet

Abstract

Yigong landslide is the largest landslide in China with super high speed and long distance coverage.It locates on the bank of the Yigong\|Zangbu in Yigong village,Bomi county,Tibet.The longest horizontal displacement is 6\^7\|7\^0?km.The biggest width,length and thickness of the landslide accumulation area are about 3\^0?km,4\^6?km and 80?m.The total surface area is 8\^69?km\+2 and the total volume is 3\^0×10\+8m\+3.The sliding process took only 3?min at the average speed of 37\|39?m/s.The disjointed rock mass formed by high speed collision distributes at the middle and the back of the landslide body.Fragmental products with a great deal of air,dust and water stack at the foreside and two sides of the landslide body.The shear stress is produced by the speed difference between the main line and the sides of the sliding body,and the main stream of the landslide is blocked by the original accumulation,therefore,the two sides of the sliding body present a typical levorotatory and dextral eddy characteristics.The high density air mass with sand,stone and water impacts the two sides and the leading edge of the high\|speed fragmental flood.The difference of density clearly presents at the front and two sides of the main accumulation area,and it is not completely symmetrical because of the original landform.The landslide has obvious air cushion impression in the process of high\|speed movement.When it falls and stops,a great deal of air is released with local collapse.The landslide is controlled not only by regional crustal rising,abundant rainfall and faults,but also by landform,structure of the strata,physical and mechanical properties,primary structural surface and secondary fissure by thawing.Ice\|snow melting has made the intragranitic pressure of pore water increased and led to mountain collapse(the volume of one collapse is 3\^0×10\+7m\+3 and the height is about 2580?m),activating the high\|speed landslide consequently and showing an entirety characteristic of collapse\|landslide.Unlike other wriggled large\|scale landslide,this landslide has the character of uncertainty and posthumousness.Considering the huge collapse\|landslide and its spatial coverage changing with time,it is noticed that in a specific spatial\|temporal coverage,large amount of ice\|snow melting leads to mountain collapse,and mountain collapse induces super high\|speed long distance landslide,and the landslide body blocks the Yigong\|Zangbu to be a lake submerging the farmland,tea\|making farmland,grass land,houses and forest,and then the lake flooded Yigong\|Zangbu,Palong\|Zangbu,Yalu\|Zangbu.As a result,the slopes in the river valley are apt to occur shallow retrogressive landslides and collapses.The landslide is actually a huge geological hazard chain with temporal\|spatial series characteristics.