Sinkhole risk in Smyth County, VA: Sinkhole country

Sinkhole country

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

On soluble rock: 55%
At or near the surface: 55%
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 246 of Smyth County's 451 square miles on soluble rock, 246 of them with the rock at or near the surface. With about 29,137 residents (65 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 537 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Smyth County

The closest county with no soluble rock mapped is Grayson County, VA, about 22 miles southeast. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Tazewell County, VA 20 mi north · 43% at surface
Grayson County, VA 22 mi southeast · 0% at surface
Washington County, VA 24 mi west · 62% at surface
Wythe County, VA 26 mi east · 64% at surface
Ashe County, NC 28 mi south · 0% at surface
Bland County, VA 30 mi northeast · 31% at surface

What Smyth County is built on

The largest mapped soluble unit here is the Shady Dolomite (dolostone (dolomite)), Cambrian in age, covering about 12% of the county. Next is the Rome Formation at 8%.

The county also lies over the Saltville, Virginia, 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 Virginia

Smyth County ranks 21 of 133 in Virginia for soluble rock at the surface, and sits above 88% of US counties on that measure.