Sinkhole risk in Polk 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: 28%
At or near the surface: 2%
Buried under cover: 26%

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 121 of Polk County's 439 square miles on soluble rock, 8 of them with the rock at or near the surface. With about 5,269 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 308 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 26% under cover still counts, and how these percentages are measured.

Counties around Polk County

The nearest county rated sinkhole country is Kearney County, NE, about 86 miles southwest. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

York County, NE 22 mi south · 0% at surface
Butler County, NE 23 mi east · 0% at surface
Merrick County, NE 24 mi west · 79% at surface
Nance County, NE 26 mi northwest · 31% at surface
Platte County, NE 27 mi north · 19% at surface
Seward County, NE 31 mi southeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 28% of the county.

Against the rest of Nebraska

Polk County ranks 29 of 93 in Nebraska for soluble rock at the surface, and sits above 57% of US counties on that measure.