Sinkhole risk in Grand Isle County, VT: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 47%
At or near the surface: 1%
Buried under cover: 46%

What to do about a house in Grand Isle County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 38 of Grand Isle County's 82 square miles on soluble rock. With about 7,528 residents (92 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 248 map points about 0.6 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 46% under cover still counts, and how these percentages are measured.

Counties around Grand Isle County

The nearest county rated sinkhole country is Union County, PA, about 326 miles southwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Franklin County, VT 20 mi east · under 1% at surface
Clinton County, NY 20 mi west · under 1% at surface
Chittenden County, VT 26 mi southeast · 0% at surface
Lamoille County, VT 35 mi east · 0% at surface
Washington County, VT 50 mi southeast · 0% at surface
Orleans County, VT 51 mi east · under 1% at surface

What Grand Isle County is built on

The largest mapped soluble unit here is the Stony Point Formation (black shale), Ordovician in age, covering about 34% of the county. Next is the Iberville Formation at 4%.

Against the rest of Vermont

Grand Isle County ranks 1 of 14 in Vermont for soluble rock at the surface, and sits above 56% of US counties on that measure.