As the ocean dropped Florida became covered by plants and soil, and subject to rainwater. As rain falls through the sky it absorbs carbon dioxide, making it slightly acidic. All stone is subject to this acid, but limestone dissolves especially rapidly, and its cracked, fractured structure lets the water seep down through it. Karstic areas have few streams. A sinkhole forms when the roof of an underground cave collapses and the rock and soil above it drop down to fill the void.
Sinkholes occasionally make the news by swallowing buildings, roads, and trucks.
Since water often lies just below the ground in Florida, these sinkholes often fill with water. They often have no streams leading in or out of them, steep sides, and a round shape. The phosphate mines We first noticed these mines in a photorevised map, not in Landsat images. This is not a full revision, but it makes for great change maps. Now look at the Homeland, Florida map from 1952, photorevised in 1986.