SinkholeOdds

Sinkhole risk in Ottawa 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
25%
At or near the surface
0%
Buried under cover
25%

What to do about a house in Ottawa County

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

That works out to roughly 139 of Ottawa County's 564 square miles on soluble rock. With about 306,235 residents (543 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 304 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 25% under cover still counts.

Counties around Ottawa County

The nearest county rated sinkhole country is Muskegon County, MI, about 28 miles north, close enough that the same rock may run under the county line. None of the 6 closest counties land in the same band, so Ottawa County stands out from its surroundings.

The rock underneath

The largest mapped soluble unit here is the Michigan Formation (black shale), Mississippian in age, covering about 24% of the county. Next is the Bayport Limestone at under 1%.

24% 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

Ottawa County ranks 73 of 83 in Michigan for soluble rock at the surface, and sits above 0% of US counties on that measure.