Sinkhole risk in Monroe County, IN: Sinkhole country

Sinkhole country

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

On soluble rock: 58%
At or near the surface: 54%
Buried under cover: 4%

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 Monroe County's 395 square miles on soluble rock, 213 of them with the rock at or near the surface. With about 140,702 residents (357 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 334 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Monroe County

The closest county with no soluble rock mapped is Brown County, IN, about 16 miles east. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Brown County, IN 16 mi east · 0% at surface
Owen County, IN 20 mi northwest · 16% at surface
Lawrence County, IN 22 mi south · 71% at surface
Morgan County, IN 23 mi north · 2% at surface
Greene County, IN 27 mi west · 20% at surface
Jackson County, IN 31 mi southeast · 2% at surface

What Monroe County is built on

The largest mapped soluble unit here is the Sanders Group (limestone), Mississippian in age, covering about 29% of the county. Next is the Blue River Group at 19%.

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

Monroe County ranks 6 of 92 in Indiana for soluble rock at the surface, and sits above 88% of US counties on that measure.