Sinkholes can be both costly and deadly. The US Geological Survey estimates that sinkholes cause approximately $300 million in damage per year. Natural sinkholes form in Karst terrain—areas with bedrock that can be dissolved by groundwater, which are typically salt beds, limestone or other carbonate rock. Florida, which has large amounts of underground limestone, is particularly susceptible.
Natural sinkholes form when acidic water dissolves the bedrock, forming pathways and channels that are then filled with “overburden,” an upper layer of rock and soil. Man-made sinkholes can occur in any type of terrain, and may form when cracked or leaking pipes provide space for overburden to fall into a pipe and be carried away.