Sinkhole risk in Seward County, KS: 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 Seward County

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

That works out to roughly 3 of Seward County's 640 square miles on soluble rock, 3 of them with the rock at or near the surface. With about 21,276 residents (33 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 399 map points about 1.3 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 ground with no limestone still opens up.

Counties around Seward County

The nearest county rated sinkhole country is Clark County, KS, about 57 miles east. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Stevens County, KS 25 mi west · 0% at surface
Haskell County, KS 26 mi north · 0% at surface
Meade County, KS 28 mi east · 15% at surface
Grant County, KS 35 mi northwest · 0% at surface
Beaver County, OK 36 mi southeast · 5% at surface
Gray County, KS 45 mi northeast · under 1% at surface

Which formation it is

The largest mapped soluble unit here is the Ogallala Formation (arkose), Miocene in age, covering about under 1% of the county.

The county also lies over the Permian Basin, Anadarko Basin,Dalhart Basin, Palo Duro Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Kansas

Seward County ranks 91 of 105 in Kansas for soluble rock at the surface, and sits above 53% of US counties on that measure.