Abstract : The simulation of landslide hazards is a key point in the prevention of natural disasters, since it enables to compute risk maps and helps to design protection works. We present a 3D simulator that handles both rock-falls and mud-flows. The terrain model is built from geological and vegetation maps, superimposed on a DEM. Since the exact elevation of the terrain is unknown at the rock's scale, the simulator uses a series of stochastic simulations, where low scale geometry is slightly randomized at each impact, to compute an envelop of risk areas. Computations are optimized using an implicit formulation of surfaces and a space-time adaptive algorithm for animating the particle system that represents the mud flow.