Sinkhole risk in Jefferson County, KY: Sinkhole country

Sinkhole country

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

On soluble rock: 60%
At or near the surface: 59%
Buried under cover: 1%

The next step for one property

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

That works out to roughly 229 of Jefferson County's 381 square miles on soluble rock, 223 of them with the rock at or near the surface. With about 793,881 residents (2,085 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 517 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Jefferson County

The closest county with no soluble rock mapped is Spencer County, IN, about 75 miles west. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Bullitt County, KY 15 mi south · 42% at surface
Floyd County, IN 16 mi northwest · 29% at surface
Oldham County, KY 18 mi northeast · 88% at surface
Clark County, IN 20 mi north · 3% at surface
Spencer County, KY 22 mi southeast · 56% at surface
Shelby County, KY 24 mi east · 68% at surface

What Jefferson County is built on

The largest mapped soluble unit here is the Louisville Limestone and Waldron Shale, undivided (limestone), Silurian in age, covering about 20% of the county. Next is the Drakes Formation at 15%.

The county also lies over the Illinois Basin, 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 Kentucky

Jefferson County ranks 29 of 120 in Kentucky for soluble rock at the surface, and sits above 89% of US counties on that measure.