Sinkhole risk in Knox County, TN: Sinkhole country

Sinkhole country

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

On soluble rock: 95%
At or near the surface: 95%
Buried under cover: 0%

What to do about a house in Knox County

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

That works out to roughly 482 of Knox County's 508 square miles on soluble rock, 482 of them with the rock at or near the surface. With about 506,748 residents (997 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 603 map points about 0.9 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 Knox County

The closest county with no soluble rock mapped is Morgan County, TN, about 40 miles west. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Anderson County, TN 17 mi northwest · 50% at surface
Union County, TN 21 mi north · 89% at surface
Blount County, TN 21 mi south · 58% at surface
Sevier County, TN 27 mi southeast · 36% at surface
Loudon County, TN 28 mi southwest · 99% at surface
Jefferson County, TN 28 mi east · 100% at surface

What Knox County is built on

The largest mapped soluble unit here is the Unnamed (upper part of Knox Group), including Newala Formation, Mascot Dolomite, Kingsport Formation, Longview Dolomite, and Chepultepec Dolomite (dolostone (dolomite)), Ordovician in age, covering about 12% of the county. Next is the Ottosee Shale at 11%.

Against the rest of Tennessee

Knox County ranks 5 of 95 in Tennessee for soluble rock at the surface, and sits above 98% of US counties on that measure.