Sinkhole risk in Madison County, AL: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock: 59%
At or near the surface: 59%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 476 of Madison County's 802 square miles on soluble rock, 476 of them with the rock at or near the surface. With about 423,355 residents (528 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 313 map points about 1.6 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Madison County

The closest county with no soluble rock mapped is Cullman County, AL, about 47 miles southwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Limestone County, AL 25 mi west · 50% at surface
Lincoln County, TN 26 mi north · 62% at surface
Morgan County, AL 27 mi southwest · 56% at surface
Jackson County, AL 32 mi east · 60% at surface
Marshall County, AL 34 mi southeast · 29% at surface
Franklin County, TN 37 mi northeast · 66% at surface

The rock underneath

The largest mapped soluble unit here is the Tuscumbia Limestone (limestone), Mississippian in age, covering about 37% of the county. Next is the Monteagle Limestone at 16%.

Against the rest of Alabama

Madison County ranks 6 of 67 in Alabama for soluble rock at the surface, and sits above 90% of US counties on that measure.