How do sinkholes form and where do they occur?
A sinkhole is an enclosed depression formed by subsidence or dissolution at the land surface. In karst regions, voids within soluble rock may contribute. Not every depression develops at the same rate or through one mechanism.
Underground voids and the surface
Water enlarges fractures in rocks such as limestone. Overlying material may sag slowly into openings or collapse suddenly after losing support. Groundwater-level changes can affect stability in some settings, but water extraction alone does not explain every sinkhole. Rock type, cover and water circulation govern local risk.
Assessing risk
New cracks and settling may warn of trouble, but visible signs may also be absent. Geological mapping, drilling and suitable geophysical methods are combined. Mining or infrastructure collapse can produce similar-looking depressions through different processes. Dumping waste in karst hollows also threatens water sources because pollutants may move quickly underground.