SinkholeOdds

Sinkhole risk in Johnson 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
13%
At or near the surface
0%
Buried under cover
13%

What to do about a house in Johnson County

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

That works out to roughly 43 of Johnson County's 320 square miles on soluble rock. With about 170,614 residents (532 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 400 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Read next: why gypsum and salt move faster than limestone, and why the 13% under cover still counts.

Counties around Johnson County

The nearest county rated sinkhole country is Monroe County, IN, about 33 miles southwest, close enough that the same rock may run under the county line. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Which formation it is

The largest mapped soluble unit here is the Muscatatuck Group (limestone), Devonian in age, covering about 13% of the county.

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

Johnson County ranks 59 of 92 in Indiana for soluble rock at the surface, and sits above 0% of US counties on that measure.