SinkholeOdds

Sinkhole risk in Union County, FL: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock
100%
At or near the surface
50%
Buried under cover
50%

The next step for one property

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

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 244 of Union County's 244 square miles on soluble rock, 122 of them with the rock at or near the surface. With about 15,738 residents (65 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 247 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: what Florida insurers have to cover, and why gypsum and salt move faster than limestone.

Counties around Union County

The closest county with no soluble rock mapped is Gulf County, FL, about 174 miles west. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

The rock underneath

The largest mapped soluble unit here is the Hawthorn Group, Coosawhatchie Formation (sand), Miocene in age, covering about 50% of the county. Next is the Hawthorn Group, Coosawhatchie Formation at 47%.

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

Union County ranks 26 of 67 in Florida for soluble rock at the surface, and sits above 87% of US counties on that measure.