Solution holes form in the Miami Limestone of the Florida Everglades when water acidifies as it steeps in ground vegetation, and then chemically reacts with the calcium carbonate contained in the bedrock. One of the plant materials most important to this acidification process is the pine needle of the Florida Slash Pine aka Dade County Pine. As rain water pools up as seen in the above photo, over thousands of years, a millimeter at a time, solution holes form through the dissolution of the limestone.
Want to know more. Read my book Hidden Springs of The Everglades.