Sinkhole risk in Clark County, IN: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 44%
At or near the surface: 3%
Buried under cover: 41%

What this means before you buy

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 165 of Clark County's 372 square miles on soluble rock, 11 of them with the rock at or near the surface. With about 127,479 residents (342 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 514 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Clark County

The nearest county rated sinkhole country is Oldham County, KY, about 15 miles east, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Scott County, IN 14 mi north · 2% at surface
Oldham County, KY 15 mi east · 88% at surface
Floyd County, IN 15 mi southwest · 29% at surface
Jefferson County, KY 20 mi south · 59% at surface
Trimble County, KY 22 mi northeast · 16% at surface
Washington County, IN 23 mi west · 62% at surface

Which formation it is

The largest mapped soluble unit here is the Muscatatuck Group (limestone), Devonian in age, covering about 24% of the county. Next is the Louisville Limestone through Brassfield Limestone at 13%.

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 Indiana

Clark County ranks 20 of 92 in Indiana for soluble rock at the surface, and sits above 60% of US counties on that measure.