SinkholeOdds

Sinkhole risk in Webster 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
28%
At or near the surface
0%
Buried under cover
28%

What to do about a house in Webster County

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

That works out to roughly 197 of Webster County's 716 square miles on soluble rock. With about 36,909 residents (52 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 363 map points about 1.4 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 28% under cover still counts.

Counties around Webster County

The nearest county rated sinkhole country is Clayton County, IA, about 148 miles east. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

The rock underneath

The largest mapped soluble unit here is the Meramec Series (limestone), Late Mississippian in age, covering about 17% of the county. Next is the Ft. Dodge Beds at 6%.

6% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

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

Webster County ranks 95 of 99 in Iowa for soluble rock at the surface, and sits above 0% of US counties on that measure.