Sinkholes most commonly occur in karst terrain: regions where limestone, gypsum, salt beds, or other carbonate rock can be dissolved. Water eats away at the rock until a pit is formed. When the roof—the sediment layer that had been on top of the rock before it deteriorated—no longer supports itself, it collapses into the pit.
Sinkholes that occur on private property are the homeowner’s responsibility. Insurance may cover an evaluation and the repair if it is actually a sinkhole and not a subsidence incident—a manmade problem caused by things like collapsed or broken sewer pipes and drainpipes, broken septic tanks and buried trash, or soil that wasn’t properly compacted after excavation work.
There are two main types of sinkholes: cover subsidence and cover collapse.