SinkholeOdds

Sinkhole risk in Pulaski 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
24%
At or near the surface
7%
Buried under cover
17%

What this means before you buy

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

That works out to roughly 47 of Pulaski County's 199 square miles on soluble rock, 13 of them with the rock at or near the surface. With about 4,879 residents (24 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 253 map points about 0.9 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 17% under cover still counts.

Counties around Pulaski County

The nearest county rated sinkhole country is Union County, IL, about 20 miles north, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

What Pulaski County is built on

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 13% of the county. Next is the Upper Valmeyeran (Aux Vases, Ste. Genevieve, St. Louis) Series at 6%.

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

Pulaski County ranks 13 of 102 in Illinois for soluble rock at the surface, and sits above 65% of US counties on that measure.