A sinkhole is a depression or hole in the ground caused by the collapse of a surface layer, often due to the dissolution of underlying carbonate rocks such as limestone. Sinkholes are significant in karst geology for understanding subsurface erosion, groundwater flow, and the hazards associated with land subsidence.
Reference: Ford, D. C., & Williams, P. W. (2007). “Karst Hydrogeology and Geomorphology.” John Wiley & Sons.