Erosion includes all processes that result in the physical wearing down of the surface of the earth. Erosion processes are complex, consisting of "natural" {geological) erosion and "accelerated" {~an induced) erosion. Natural erosion rates are very high in Nepal because of the constant tectonic uplifting of the major mountain ranges and consequent down cutting of the river systems. The net result of these unrelenting forces are unstable slopes that cannot maintain their river-canyon form. Natural erosion is characterized by different forms of mass wasting, particularly rock failures, landslides, slumps, riverbank cutting and gullying.