Debris flows in Jiangjia Gully present a variety of appearances and cover a wide spectrum of motion regime. Each event consists of surges of various viscosities, densities, velocities and discharges. Field observations indicate that slope and channel processes are randomly distributed over the source areas and conform to the category of spatial Poisson process, meaning that the processes are independent of one another and the intensity is proportional to the area of the local source. Then a debris flow surge is actually a pooled process and the resulted intensity. This agrees well with the observation in Jiangjia Gully. From the stochastic viewpoint, debris flow depends primarily on the spatial heterogeneity of valley and the local processes in tributaries, but not so much on the full-valley parameters.