Sinkhole risk in Jefferson 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: 21%
At or near the surface: 21%
Buried under cover: 0%

What to do about a house in Jefferson 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 232 of Jefferson County's 1,112 square miles on soluble rock, 232 of them with the rock at or near the surface. With about 664,744 residents (598 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 594 map points about 1.4 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 Jefferson County

The nearest county rated sinkhole country is Talladega County, AL, about 43 miles east. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Shelby County, AL 24 mi southeast · 30% at surface
Walker County, AL 28 mi northwest · 0% at surface
Blount County, AL 35 mi northeast · 23% at surface
St. Clair County, AL 36 mi east · 45% at surface
Bibb County, AL 39 mi south · 12% at surface
Cullman County, AL 40 mi north · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Chepultepec and Copper Ridge Dolomites undifferentiated (dolostone (dolomite)), Ordovician-Cambrian in age, covering about 5% of the county. Next is the Ketona Dolomite at 4%.

Against the rest of Alabama

Jefferson County ranks 30 of 67 in Alabama for soluble rock at the surface, and sits above 75% of US counties on that measure.