SinkholeOdds

Sinkhole risk in Adams County, IL: 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
55%
At or near the surface
under 1%
Buried under cover
54%

What to do about a house in Adams County

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

That works out to roughly 471 of Adams County's 855 square miles on soluble rock, 7 of them with the rock at or near the surface. With about 64,109 residents (75 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 354 map points about 1.6 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and why the 54% under cover still counts.

Counties around Adams County

The nearest county rated sinkhole country is Calhoun County, IL, about 63 miles southeast. 4 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 Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series (limestone), Mississippian in age, covering about 21% of the county. Next is the Lower Valmeyeran (Keokuk-Sedalia) Series at 15%.

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 Illinois

Adams County ranks 21 of 102 in Illinois for soluble rock at the surface, and sits above 54% of US counties on that measure.