Sinkhole risk in Madison County, NE: 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: 34%
At or near the surface: 4%
Buried under cover: 29%

What to do about a house in Madison County

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

That works out to roughly 194 of Madison County's 573 square miles on soluble rock, 25 of them with the rock at or near the surface. With about 35,579 residents (62 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 391 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 29% under cover still counts, and how these percentages are measured.

Counties around Madison County

The nearest county rated sinkhole country is Knox County, NE, about 52 miles north. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Stanton County, NE 22 mi east · 0% at surface
Platte County, NE 24 mi south · 19% at surface
Pierce County, NE 25 mi north · 0% at surface
Boone County, NE 28 mi southwest · 0% at surface
Antelope County, NE 30 mi northwest · 0% at surface
Wayne County, NE 32 mi northeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 34% of the county.

Against the rest of Nebraska

Madison County ranks 26 of 93 in Nebraska for soluble rock at the surface, and sits above 62% of US counties on that measure.