Dispersive soils subside by actual soil-mass loss through erosion and the formation of subsurface pipes and fissures, which collapse at the surface to create sinkholes and other pseudo-karst landforms (see figure at lower right).  Certain soil and rock contain soluble minerals like gypsum.  Dissolution and removal of the soluble mineral constituents of these types of soil or bedrock can also cause ground settlement.

Road damage from a sinkhole near Olathe, Colorado.  Photo by Jon White.