In general, sinkholes form by the subsidence of unconsolidated materials or soils into voids created by the dissolution of the underlying soluble bedrock. The rock exposed in a collapsed sinkhole is usually weathered and rounded, but some sinkholes contain freshly broken rock along their steep sides. Where sinkholes and caves have formed by the dissolution of soluble rock, such as limestone, dolomite, and gypsum, surface water is uncommon and streams may sink into the ground. This type of topography, formed by dissolution, is referred to as karst terrain. In karst terrain, sinkholes are input points where surface water enters the groundwater system.
Sinkholes are the result of differential subsidence of the land surface.
The term subsidence is commonly used to imply a gradual sinking, but it also can refer to an instananeoust or catastrophic collapse. Although the formation of sinkholes is a natural process in karst terrains, man-made modifications to the hydrology of these areas commonly results in the acceleration of this process. The lowering of the water table in unconsolidated materials or soils, especially near the soil-bedrock interface, can result in the draining of voids caused by the dissolution of bedrock or the removal of soil by groundwater flow. Wet soil weighs more and has less strength than if it were dry. If the strength of the wet soil is insufficient the soil arch will fail.