The Donghekou landslide-debris flow is a typical rapid long run-out landslide triggered by great Wenchuan earthquake. It started from the elevation of 1300m and caused 780 deaths, with a total long run-out of 2400m. Field investigations show that this landslide is mainly affected by a fault with the trending of N50~E and the width of 80-100m. When earthquake happened, the rockmass located in fault zone broken first for its lower strength, and meanwhile, the landslide was started-up. During the process from start-up to stop, it experienced the following five dynamical stages, such as start-up stage, gravity speed-up stage, en- closure air cushion effect stage, impact and reentry stage and long run-out sliding accumulation stage. Finally, it reached the Honghuadi village located at the left bank of Xiasihe River, and dammed lakes occurred. The above dynamical processes are analyzed in this paper, and some useful conclusions have been gained.
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