Sinkhole risk in Alpena 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: 44%
At or near the surface: 0%
Buried under cover: 44%

The next step for one property

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

That works out to roughly 250 of Alpena County's 572 square miles on soluble rock. With about 28,903 residents (51 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 332 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 why the 44% under cover still counts.

Counties around Alpena County

The nearest county rated sinkhole country is Iosco County, MI, about 35 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.

Alcona County, MI 18 mi south · under 1% at surface
Presque Isle County, MI 25 mi north · under 1% at surface
Iosco County, MI 35 mi south · 0% at surface
Montmorency County, MI 36 mi west · 0% at surface
Oscoda County, MI 37 mi west · 0% at surface
Ogemaw County, MI 52 mi southwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Traverse Group (limestone), Middle Devonian in age, covering about 44% 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

Alpena County ranks 15 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.