The genetic mechanism of Gangudi landslide

A huge landslide-Gangudi landslide in the western slope of Erlangshan, i.e., the left bank of Daduhe river near Luding county, is mainly composed of the late Proterozoic granite. why it occured in such a slope and how it happened? the present paper tries to reveal the answer. The Landform of Gangudi landslide is a round-backed armchair shape with a convexity-westward platform. The trailing edge is arc-shaped concave, the north edge is deeply cutting valley-Wajiaogou, the south edge is relatively shallow valley. The length of the slope along the Daduhe river is about 1500m, the elevation is 1450m (the landslide toe) -1750m(the landslide top). the source region is 2520m above s.l., horizontal movement distance of the landslide is about 1500m and the vertical movement distance of the landslide is 770m. the volume is about 1.8x108m3, it is compsed the completed disagregated granite block, granule, sands and weathering soil. It dammed the Daduhe River 5-6x104years B.P. with 300m dam height and formed a large reservoir, whose end reached to the mouth of Wasigou and the length of the reservoir is about 35km. There are check-up lake sediments in the upstream. According to the comprehensive investigation, we believe that a specail engineering envrionment is the main cause for the landslide: Gangudi region is the junction of the South-North (SN) strike Daduhe fracture and North-East (NE) strike Longmenshan fracture, and NNW strike Xianshuihe fracture. The SN strike texture plane and dolerite veins are well developed. They cut the granite slope into a bedding slope. The Daduhe river flows from the north to the south, the free surface dipping to the west on the left bank of Daduhe river makes it possible for the granite slope to form a huge landslide. The high intensity (more than 9) is the induced factor for landslide forming. The two factors reactivited, and forming the huge landslide. The movement process can be concluded: the strong unloading along the antecedent consequent texture plane in Mt. ridge make the slope be in lower safety statues, triggerring by strong earthquake and the landform amplified effect, the perpherical rockmass on the left bank is thrown from the source region at relatively 700m. High above the river bottom and flied about 1.5km and accumulated on the bottom of 1450m above sea level. It dammed the Daduhe river and formed a huge reservoir