Geologic processes that act on the land's surface are described below. Surface geologic processes. Most young surface deposits of the deserts were created by water carrying sediment by alluvial and colluvial processes. The term landslide includes a wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Slow movement of landslides and gradual creep of rock and soil downslope can be as destructive as rapid landslides and debris flows but are not catastrophic, and cause less loss of life.
Landslides are much more likely to occur when the slopes are saturated by water.
Prolonged rainfall and rapid melt of thick snowpack can trigger landslides on steep slopes underlain by weak materials. Gros Ventre landslide , Wyoming. Photograph taken in 1931 of landslide triggered by rainfall and snowmelt in 1925. Landslide dammed the Gros Ventre River, creating a lake that later drained catastrophically when the landslide dam failed, killing people downstream. Madison slide , with Earthquake Lake behind it.