The Slumgullian mudflow in the San Juan Mountains, Colorado. Some of the mass movement processes operating on cohesive materials occur over very long time spans. One of the most widespread of these processes is soil creep . The cyclical effects of temperature fluctuations, variations in moisture, and gravity on inclined soil sediments often cause this process. The following animation models the process of soil creep.
Soil creep can only occur on a slope.
It occurs when some mechanism causes the surface soil layer to expand and contract. Mechanisms that can cause this expansion and contraction include cyclical changes in soil temperature and mositure. Expansion moves soil particles upward and perpendicular to the angle of the slope. When contraction occurs the soil particles move downward under the influence of gravity. As depicted in the animation, the angle of this movement differs from the angle of the movement due to expansion.