Sinkhole risk in Blount County, AL: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 23%
At or near the surface: 23%
Buried under cover: 0%

What to do about a house in Blount County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 150 of Blount County's 645 square miles on soluble rock, 150 of them with the rock at or near the surface. With about 60,163 residents (93 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 512 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Blount County

The nearest county rated sinkhole country is Morgan County, AL, about 37 miles northwest, close enough that the same rock may run under the county line. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Cullman County, AL 20 mi northwest · 0% at surface
St. Clair County, AL 23 mi southeast · 45% at surface
Marshall County, AL 27 mi northeast · 29% at surface
Etowah County, AL 31 mi east · 46% at surface
Jefferson County, AL 35 mi southwest · 21% at surface
Morgan County, AL 37 mi northwest · 56% at surface

The rock underneath

The largest mapped soluble unit here is the Bangor Limestone (limestone), Mississippian in age, covering about 6% of the county. Next is the Tuscumbia Limestone and Fort Payne Chert undivided at 5%.

Against the rest of Alabama

Blount County ranks 29 of 67 in Alabama for soluble rock at the surface, and sits above 76% of US counties on that measure.