Sinkhole risk in Henry County, IA: 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: 100%
At or near the surface: 0%
Buried under cover: 100%

What to do about a house in Henry County

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

That works out to roughly 432 of Henry County's 434 square miles on soluble rock. With about 19,361 residents (45 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 400 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Henry County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 118 miles northeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Des Moines County, IA 19 mi east · 3% at surface
Jefferson County, IA 22 mi west · 0% at surface
Louisa County, IA 22 mi northeast · 0% at surface
Lee County, IA 24 mi south · 2% at surface
Washington County, IA 26 mi north · 0% at surface
Van Buren County, IA 27 mi southwest · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Osage Series (dolostone (dolomite)), Early Mississippian in age, covering about 56% of the county. Next is the Meramec Series at 34%.

The county also lies over the Forest City 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 Iowa

Henry County ranks 50 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.