Sinkhole risk in Howard 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: 11%
At or near the surface: 11%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 64 of Howard County's 569 square miles on soluble rock, 64 of them with the rock at or near the surface. With about 6,572 residents (12 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 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 gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Howard County

The nearest county rated sinkhole country is Kearney County, NE, about 54 miles southwest. None of the 6 closest counties land in the same band, so Howard County stands out from its surroundings.

Sherman County, NE 24 mi west · 0% at surface
Hall County, NE 24 mi south · 33% at surface
Greeley County, NE 24 mi north · 0% at surface
Merrick County, NE 25 mi east · 79% at surface
Nance County, NE 30 mi northeast · 31% at surface
Valley County, NE 34 mi northwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Pierre Shale (shale), Late Cretaceous in age, covering about 7% of the county. Next is the Niobrara Formation at 5%.

7% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of Nebraska

Howard County ranks 23 of 93 in Nebraska for soluble rock at the surface, and sits above 69% of US counties on that measure.