Collapse Sinkholes

Collapse sinkholes are the most dramatic of the three sinkhole types; they form with little warning and leave behind deep, steep-sided holes. One mechanism for the formation of a collapse sinkhole is illustrated below. Notice that the geologic conditions include soluble bedrock (such as limestone) covered by relatively thick deposits of sediments. This type of sinkhole can form naturally but is often affected by human activities.

Formation of a collapse sinkhole (1).

(1) There is no evidence of land subsidence, but small- to medium-sized cavities have already formed in the bedrock.

Formation of a collapse sinkhole (2).

(2) Cavities in the bedrock continue to grow larger but remain filled with groundwater. Water pressure helps to support the thinner, weaker roof of a large cavity.

Formation of a collapse sinkhole (3).

(3) As groundwater levels drop naturally during the dry season (or are drawn down by pumping), the cavities become dewatered. The weight of overburden now exceeds the strength of the cavern roof, and the overburden collapses into the cavern, forming a sinkhole.

source: Hydrology of Central Florida Lakes--A Primer.