Downhill creep
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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 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.
[edit] Modeling Regolith Diffusion
For shallow to moderate slopes, diffusional sediment flux is modeled linearly as (Culling, 1960; McKean et al., 1993)
<math>q_s = k_d S \,\!</math>
where <math>k_d\,\!</math> is the diffusion constant, and <math>S\,\!</math> is slope. For steep slopes, diffusional sediment flux is more appropriately modeled as a non-linear function of slope (Roering et al., 1999)
<math>q_s = \frac{k_d S}{1 - (S/S_c)^2}\,\!</math>
where <math>S_c\,\!</math> is the critical gradient for sliding of dry soil.
[edit] Bibliography
- Culling, 1960.
- McKean et al., 1993.
- Roering, Kirchner and Dietrich, 1999. Evidence for nonlinear diffusive sediment transport on hilslopes and implications for landscape morphology. Water Resour. Res., 35:853-887.
