SinkholeOdds

Sinkhole risk in Mahaska 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
46%
At or near the surface
0%
Buried under cover
46%

What to do about a house in Mahaska County

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

That works out to roughly 260 of Mahaska County's 571 square miles on soluble rock. With about 22,034 residents (39 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 391 map points about 1.2 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 46% under cover still counts.

Counties around Mahaska County

The nearest county rated sinkhole country is Clayton County, IA, about 124 miles northeast. 6 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 Meramec Series (limestone), Late Mississippian in age, covering about 44% of the county. Next is the Osage Series at 2%.

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

Mahaska County ranks 64 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.