Sinkholes form in karst terrain principally from the collapse of surface sediments into underground voids and cavities in the limestone bedrock. Slightly acidic ground water slowly dissolves cavities and caves in the limestone over a period of many years. When the cavity enlarges to the point that its ceiling can no longer support the weight of overlying sediments, the earth collapses into the cavity.
Karst terrain is a type of topography that is formed by dissolution of bedrock in areas underlain by limestone, dolostone or, as in some western states, gypsum. Such terrain has underground drainage systems that are reflected on the surface as sinkholes, springs, disappearing streams or even caves.