A lot of “sinkholes” now appearing in Florida aren’t natural limestone sinkholes, although we certainly have plenty of those, this is karst country.
But there’s also the type of voids created some decades ago, when developers dozed up huge swaths of saw palmetto and other trees in low areas along the coast where instead of limestone there’s often just deep cypress dome peat bogs, and rather than burn these mountains of wood or haul it away it was used as fill in ponds, swamps and other spots that otherwise would have been too low to build on.
There could be football field size voids left this way that are far more unstable than a limestone sink. Filling with downed trees and brush was a cost saving effort for contractors since fill dirt isn’t cheap in Florida, plus it hid the tell-tale signs of a possible flood prone area by burying saw palmetto. Then they piled many feet of typical Florida sandy soil on top and built on it, and covered it with a thin layer of better soil so it could support lawns.
For decades the houses stood fine atop twenty foot tall piles of logs and branches, but eventually the buried wood rotted away and settled, leaving a void. The void might slowly sank with the weight of the house, especially if networks of big tree roots are allowed to grow, or they might collapse catastrophically if someone suddenly decides to cut old trees all at once and their roots decay, or if there’s a deluge.
In the case of the man-made sinkholes, several will often appear in the same neighborhood at roughly the same time because the houses were all built at the same time and so the hidden woodpiles beneath have rotted away at the same rate.
Which type of sinkhole this one is I don’t know, but I bet a lot of people will be looking closely at their foundations tomorrow before going to sleep.
I wonder if ground penetrating radar could detect such voids.
Wouldn't a competent inspecter be able to spot the possible problem?
Or would this “man made void” not be easily identified?