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Sinkholes: what karst is and why the ground gives way

Sinkholes form where soluble rock — limestone, gypsum, salt — dissolves underground and leaves a void that eventually collapses. The regions tracked here are all karst or evaporite landscapes, and the trigger is usually water: heavy rain, drought breaking, a burst main, or groundwater pumping.

  • 4High risk
  • 6Medium
  • 0Low
  • 10Zones tracked

The warning signs

Circular depressions appearing in a lawn or field. Fence posts, signs or trees starting to tilt or sink. Stair-step cracks in walls and foundations, doors and windows that stop closing, and cracks in floors or paving. Water pooling somewhere new, or a well or pond suddenly muddying or draining. Most collapses that injure people are preceded by days or weeks of these signs.

Where it matters for a visitor

Central Florida, the Kentucky and Missouri karst, and Texas Hill Country in the United States; the Ripon gypsum belt, Cheshire salt field, Mendips and Peak District limestone in Britain. For a traveller this is mostly context rather than a daily risk — but it explains why some parking areas, caves and show-cave paths are fenced off without obvious reason.

How to avoid it

  • Take fenced-off ground, closed paths and cordons in karst country seriously.
  • Report new depressions, tilting posts or stair-step wall cracks to the property owner or local authority.
  • Avoid entering undeveloped caves and shafts without proper equipment and training.
  • Be more alert after prolonged heavy rain, after a long drought breaks, and around any burst water main.
  • If ground starts to subside beneath you, move off it immediately and keep others back.

Where we track it

10 zones in the Dangers Here hazard database, by danger level.

High

  • Central Florida Sinkhole Belt, USA
  • Cheshire Salt Subsidence Zone, UK
  • Kentucky Karst (Mammoth Cave Region), USA
  • Ripon Gypsum Sinkhole Zone, UK

Medium

  • Mendip Hills Karst, Somerset, UK
  • Ozarks Karst, Missouri, USA
  • Peak District Limestone, Derbyshire, UK
  • Pennsylvania Carbonate Valley Sinkholes, USA
  • South Wales Carboniferous Limestone, UK
  • Texas Hill Country Karst (San Antonio), USA

Questions

Where are sinkholes a risk?

We track 10 zones for this hazard. 4 are rated high risk, including Central Florida Sinkhole Belt, USA, Cheshire Salt Subsidence Zone, UK, Kentucky Karst (Mammoth Cave Region), USA, Ripon Gypsum Sinkhole Zone, UK. 6 are rated medium and 0 low.

How do you avoid sinkholes?

Take fenced-off ground, closed paths and cordons in karst country seriously. Report new depressions, tilting posts or stair-step wall cracks to the property owner or local authority. Avoid entering undeveloped caves and shafts without proper equipment and training.

The warning signs

Circular depressions appearing in a lawn or field. Fence posts, signs or trees starting to tilt or sink. Stair-step cracks in walls and foundations, doors and windows that stop closing, and cracks in floors or paving. Water pooling somewhere new, or a well or pond suddenly muddying or draining. Most collapses that injure people are preceded by days or weeks of these signs.

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