Sinkhole risk in Northumberland County, PA: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 37%
At or near the surface: 26%
Buried under cover: 11%

What to do about a house in Northumberland 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 170 of Northumberland County's 458 square miles on soluble rock, 119 of them with the rock at or near the surface. With about 90,027 residents (197 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 422 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Northumberland County

The nearest county rated sinkhole country is Union County, PA, about 20 miles northwest, close enough that the same rock may run under the county line. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Montour County, PA 13 mi north · 40% at surface
Union County, PA 20 mi northwest · 53% at surface
Snyder County, PA 20 mi west · 38% at surface
Columbia County, PA 21 mi northeast · 4% at surface
Schuylkill County, PA 28 mi east · 2% at surface
Dauphin County, PA 31 mi south · 8% at surface

Which formation it is

The largest mapped soluble unit here is the Hamilton Group (shale), Devonian in age, covering about 22% of the county. Next is the Wills Creek Formation at 5%.

Against the rest of Pennsylvania

Northumberland County ranks 21 of 67 in Pennsylvania for soluble rock at the surface, and sits above 78% of US counties on that measure.