Sinkhole risk in Emmet County, MI: Sinkhole country

Sinkhole country

Fast-dissolving gypsum or salt beds under a large part of the county.

On soluble rock: 91%
At or near the surface: 0%
Buried under cover: 91%

What this means before you buy

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 424 of Emmet County's 468 square miles on soluble rock. With about 33,949 residents (73 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 286 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 91% under cover still counts.

Counties around Emmet County

The closest county with no soluble rock mapped is Clare County, MI, about 111 miles south. None of the 6 closest counties land in the same band, so Emmet County stands out from its surroundings.

Cheboygan County, MI 25 mi east · 1% at surface
Charlevoix County, MI 27 mi west · 11% at surface
Antrim County, MI 41 mi south · 0% at surface
Mackinac County, MI 43 mi north · under 1% at surface
Otsego County, MI 44 mi southeast · 0% at surface
Chippewa County, MI 55 mi northeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Traverse Group (limestone), Middle Devonian in age, covering about 39% of the county. Next is the Detroit River Group at 39%.

39% 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 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

Emmet County ranks 32 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.