Sinkhole risk in Des Moines 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: 99%
At or near the surface: 3%
Buried under cover: 96%

What to do about a house in Des Moines County

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

That works out to roughly 410 of Des Moines County's 416 square miles on soluble rock, 10 of them with the rock at or near the surface. With about 38,411 residents (92 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 275 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Des Moines County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 112 miles northeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Henderson County, IL 15 mi southeast · 0% at surface
Henry County, IA 19 mi west · 0% at surface
Louisa County, IA 21 mi north · 0% at surface
Lee County, IA 24 mi southwest · 2% at surface
Warren County, IL 30 mi east · 0% at surface
Mercer County, IL 31 mi northeast · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Osage Series (dolostone (dolomite)), Early Mississippian in age, covering about 55% of the county. Next is the Yellow Spring Group at 24%.

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

Des Moines County ranks 9 of 99 in Iowa for soluble rock at the surface, and sits above 59% of US counties on that measure.