USGS photo by Gerald Wieczorek (fair use policy)
A saturated layer of clay finally had enough on April 27, 1993, and this farmland in Tully Valley in upstate New York gave way, like so much soggy cereal, in a slump. (The U.S. Geological Survey has a full report on the landslide online.)
Slumps are landslides in which the moving material moves in a block, more or less. In the center of this photo you can see a piece of wooded land that moved downhill in one piece. The layer of clay, acting as a lubricant, allowed the land to move without falling completely apartalthough much of this slide did indeed turn to mush.
The slump below formed in shale of the Moreno Formation in central California. It is actually several slumps. Typically slumps occur in sediment, not consolidated rock, but this shale is practically clay already. (This picture is also available as a free wallpaper image.) Learn more from Landslides in a Nutshell.
Smaller slumps are found almost everywhere. The one below occurred where a stream eroded into a hillside; the flat streambed appears at the bottom of the image.
Images (c) 2002 and 2005 Andrew Alden, licensed to About, Inc. (fair use policy)
See more slumps in the Landslide Picture Gallery.