SinkholeOdds

Sinkhole risk in Alcona County, MI: 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
4%
At or near the surface
under 1%
Buried under cover
3%

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 25 of Alcona County's 675 square miles on soluble rock, 3 of them with the rock at or near the surface. With about 10,624 residents (16 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 380 map points about 1.3 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 how these percentages are measured.

Counties around Alcona County

The nearest county rated sinkhole country is Iosco County, MI, about 19 miles south, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Bedford Shale (shale), Upper Devonian in age, covering about 4% of the county.

The county also lies over the Michigan Basin; Ohio Basin; Appalachian 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 Michigan

Alcona County ranks 6 of 83 in Michigan for soluble rock at the surface, and sits above 53% of US counties on that measure.