Comments on the mechanism of soil detachment by rainfall

The mechanisms for the detachment of soil particles by raindrops can be described by a model based on three stages. In the first stage, the soil is still dry and detachment of particles results from collisions of elastic bodies. In the second stage, the soil is fluidized and impacting raindrops cause the splash of drops of the fluidized soil. In the third stage, the fluidized soil is covered by an overland flow and drops of fluidized soil may disintegrate in the overland flow. High hydration energies of soil minerals of small particle size lead to high chemical interactions between raindrop water and soil particles and a consequent decrease of detachment of particles during the first stage. During the second and third stages, high hydration energies of minerals lead to high surface tension of fluidized soil and reduce the splashing of droplets of this fluid. The present model gives an explanation for the observed fact that the rate of particle detachment is greatest in coarse- and medium-sand-size material and is reduced at either larger or smaller particle sizes. It appears that high hydration energies are responsible for the low relative detachability of small particles.