Sinkhole risk in Harrison County, IN: Sinkhole country

Sinkhole country

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

On soluble rock: 96%
At or near the surface: 94%
Buried under cover: 2%

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 462 of Harrison County's 484 square miles on soluble rock, 454 of them with the rock at or near the surface. With about 39,978 residents (83 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 269 map points about 1.3 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 Harrison County

The closest county with no soluble rock mapped is Spencer County, IN, about 51 miles west. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Floyd County, IN 14 mi northeast · 29% at surface
Meade County, KY 16 mi south · 91% at surface
Crawford County, IN 20 mi west · 83% at surface
Jefferson County, KY 24 mi east · 59% at surface
Bullitt County, KY 26 mi southeast · 42% at surface
Washington County, IN 29 mi north · 62% at surface

Which formation it is

The largest mapped soluble unit here is the Blue River Group (limestone), Mississippian in age, covering about 73% of the county. Next is the Sanders Group at 12%.

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

Harrison County ranks 1 of 92 in Indiana for soluble rock at the surface, and sits above 98% of US counties on that measure.