SinkholeOdds

Sinkhole risk in Hillsborough County, FL: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock
94%
At or near the surface
29%
Buried under cover
65%

What to do about a house in Hillsborough County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

Standard Florida homeowners policies cover only catastrophic ground cover collapse; full sinkhole coverage is a separately priced option insurers must offer.

That works out to roughly 961 of Hillsborough County's 1,023 square miles on soluble rock, 300 of them with the rock at or near the surface. With about 1,581,426 residents (1,547 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 348 map points about 1.7 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: what Florida insurers have to cover, and why gypsum and salt move faster than limestone.

Counties around Hillsborough County

The nearest county rated sinkhole country is Sarasota County, FL, about 46 miles south. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Hawthorn Group, Arcadia Formation, Tampa Member (limestone), Eocene in age, covering about 36% of the county. Next is the Hawthorn Group, Peace River Formation at 24%.

The county also lies over the Floridan shelf, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Florida

Hillsborough County ranks 44 of 67 in Florida for soluble rock at the surface, and sits above 79% of US counties on that measure.