Sinkhole risk in Brown County, NE: Not karst, but voids possible

Not karst, but voids possible

No soluble bedrock; some pseudokarst (piping or lava-tube ground).

On soluble rock: under 1%
At or near the surface: under 1%
Buried under cover: 0%

What to do about a house in Brown County

Not true karst, but soil piping or lava tubes can still open voids - mention it to an inspector.

That works out to roughly 7 of Brown County's 1,221 square miles on soluble rock, 7 of them with the rock at or near the surface. With about 2,877 residents (2 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 351 map points about 1.9 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Brown County

The nearest county rated sinkhole country is Boyd County, NE, about 69 miles northeast. None of the 6 closest counties land in the same band, so Brown County stands out from its surroundings.

Rock County, NE 26 mi east · 5% at surface
Blaine County, NE 30 mi south · 0% at surface
Keya Paha County, NE 37 mi north · 21% at surface
Loup County, NE 38 mi southeast · 0% at surface
Thomas County, NE 46 mi southwest · 0% at surface
Holt County, NE 59 mi east · 15% at surface

Which formation it is

The largest mapped soluble unit here is the Pierre Shale (shale), Late Cretaceous in age, covering about under 1% of the county.

Against the rest of Nebraska

Brown County ranks 32 of 93 in Nebraska for soluble rock at the surface, and sits above 53% of US counties on that measure.