Sinkhole risk in Northumberland County, VA: 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: 12%
At or near the surface: 12%
Buried under cover: 0%

What to do about a house in Northumberland County

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

That works out to roughly 24 of Northumberland County's 191 square miles on soluble rock, 24 of them with the rock at or near the surface. With about 12,397 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 395 map points about 0.7 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Northumberland County

The nearest county rated sinkhole country is Hertford County, NC, about 108 miles south. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Lancaster County, VA 11 mi south · 4% at surface
Middlesex County, VA 19 mi southwest · 14% at surface
Richmond County, VA 20 mi west · 23% at surface
St. Mary's County, MD 27 mi north · 15% at surface
Westmoreland County, VA 29 mi northwest · 20% at surface
King and Queen County, VA 30 mi west · 37% at surface

Which formation it is

The largest mapped soluble unit here is the Chesapeake Group (sand), Tertiary in age, covering about 12% of the county.

Against the rest of Virginia

Northumberland County ranks 53 of 133 in Virginia for soluble rock at the surface, and sits above 70% of US counties on that measure.