In insurance terms it's called a 'catastrophic ground collapse' and in 2007 Florida passed a law that all homeowners insurance policies in Florida are required to include it. Sink Hole coverage is not mandatory but must be offered. However, it covers different problems, not the one we are referring to. Sink hole coverage is more for a gradual happening such as settling and cracks in the foundation. The sudden opening of the earth is covered by the Catastrophic coverage, which we all have in our policy.
Florida Sinkhole Insurance Facts | Earth Tech