Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/landslides/whatsalandslide.shtml
A landslide is a sudden collapse of a large mass of hillside. There are many different types of landslides, where not only earth, but rock, mud, and debris flow down the side of a slope. A mudflow occurs when a slope is so heavily saturated with water that it rushes downhill as a muddy river, carrying down debris and spreading out at the base of the slope. They are faster than soil creeps but slower than landslides, but the wetter the material, the faster it moves. Mudflows are the fastest, wettest flows, while the slowest, driest ones are earthflows. Earthflows occur on clay, silt, or sand slopes, when the wet ground breaks up and falls down a mountainside, making a rounded, tongue-like shape. Another type of earth movement is the soil creep. Even on very shallow slopes, the loose, weathered material, or regolith, will eventually move downhill. It absorbs water and swells up, and when the water evaporates, the soil shrinks and moves downill a little more. Soil creeps are also known as heaves. You can tell that soil is creeping if you see tilted structures like fences, walls, power lines, and tree trunks.