Downhill creep
From Freepedia
Downhill creep is the slow progression of rock and other debris down a low grade slope; it can also refer to slow deformation of such materials as a result of prolonged pressure and stress.
Creep can be caused by the expansion of materials such as clay when they are exposed to water. Clay expands when wet, then contracts after drying. The expansion portion pushes downhill, then the contraction results in consolidation at the new offset.
Design engineers sometimes need to guard against downhill creeep during their planning to prevent building foundations from being undermined. Pilings are planted sufficiently deep into the surface material to guard against this behavior.
