Generally, collapse and landslide are the main sources of granular deposits while the initiation of deposits is triggered by the tremendous runoff from steep longitudinal gully. Substance composition, topographic condition and catchment characteristics directly affect the models of deposits initiation, and larger longitudinal grade provides better topographic condition for the initiation. Several sets of experiments on model casing were designed to simulate the failure mode of slopes under the states of stable and unstable seepages according to catchment and penetration characteristics. It was revealed from the experiments that the initiation of granular deposits had two fundamental modes, that is, fire hose effect and static liquefaction. The former one generally happens at the unsaturated slope or the slope of high permeability while the latter case occurs at the soils containing fine particles. It was concluded that the fire hose effect could generate the deep and narrow eroded channel along with the runoff, the movement distance was related to the continuous hydrodynamic force, and the transporting capacity of solid substances was weak. In addition, slope fluidization was featured with slow seepage failure at the early stage, instantaneous shear failure at the late stage, and wider channel came out due to serious erosion.