Creep

From GeoClasses

Downhill creep, or commonly just creep, is the slow progression of rock and soil down a low grade slope; it can also refer to slow deformation of such materials as a result of prolonged pressure and stress. The rate of soil creep down a slope depends on the steepness of the slope itself - the steeper the slope, the faster the creep. This is responsible for the rounded shape of hilltops.

creep of the slope over a sidewalk

trees showing the presence of creep on a hillside (the smaller trees are more obvious)

Gay Head cliffs on Martha's Vineyard, almost entirely made of clay. Notice the shape of the slopes.

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 creep during their planning to prevent building foundations from being undermined. Pilings are planted sufficiently deep into the surface material to guard against this behavior.

• From Wikipedia Downhill_creep, 19:19, 6 March 2006

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