A sinkhole is a hollow or hole that forms when the ground loses support from below. In the UK most natural sinkholes are linked to rocks that dissolve in water: limestone, chalk, gypsum and salt. Many of the collapses reported in the news, though, are caused by leaking pipes or old mine workings.
Four ways sinkholes form
The British Geological Survey groups sinkholes (also called dolines) by how they form:
- Dissolution sinkholes. Rainwater and slightly acidic groundwater slowly dissolve soluble rock at the surface, forming a hollow.
- Collapse sinkholes. A cave or void at depth fails and the collapse works its way up to the surface. Where it breaks through a layer of non-soluble rock above, this is called a caprock sinkhole.
- Suffosion and dropout sinkholes. Loose cover such as sand, soil or clay washes down into fissures in the rock below. Sandy cover tends to slump gradually (suffosion). Cohesive clay can bridge a growing cavity and then fail suddenly (dropout).
- Erosion sinkholes. Flowing water carries away weak, loose material through soil “pipes”, leaving voids behind.
Where they happen
| Rock | Typical areas | Notes |
|---|---|---|
| Gypsum (Permian) | Ripon, North Yorkshire | Gypsum dissolves much faster than limestone. BGS describes Ripon as the most susceptible area in the UK; in 1997 four garages collapsed into a subsidence hollow there. |
| Carboniferous limestone | Mendips, South Wales, Peak District, northern Pennines, Yorkshire Dales | Classic karst landscapes with caves, shakeholes and swallow holes. |
| Chalk | Dorset, Hampshire, the Chilterns and other chalk areas | Most common where chalk is covered by younger clay and sand, which can wash into solution pipes. |
| Salt | Cheshire | Natural dissolution and past brine extraction both cause subsidence, which can be hard to tell apart. |
| Durness Group limestone | Assynt, Scotland | The only notable sinkhole area in Scotland. |
What triggers a collapse
Underground cavities can exist for a very long time without reaching the surface. Collapse is usually triggered by a change, most often involving water:
- heavy rain or surface flooding, particularly where loose deposits overlie fissured rock
- leaking drains, burst water mains, soakaways or emptied swimming pools
- construction, new loads or changes to surface drainage
- pumping groundwater, which lowers the water table and removes the support it gives to cavities
- mining, through dewatering or by cutting into clay-filled voids
Not every “sinkhole” is natural. Many holes reported as sinkholes are ground collapsing into man-made voids, such as old mines, wells and tunnels, or soil washed out by a leaking pipe. In Norwich, for example, old chalk mines have caused collapses. In February 2025 several holes opened in a street in Godstone, Surrey; experts quoted at the time pointed to soil washed out by a burst water main, and to old sand workings nearby.
Warning signs
- a new circular dip or depression in a garden, field or road
- cracks in paths, driveways or walls that appear suddenly
- doors or windows that suddenly stick
- water draining unusually quickly from the surface, or a fall in pond levels
- a burst or leaking pipe on ground known to contain soluble rock
If a hole opens, keep people and pets away, and contact your local council (and your water company if a pipe may be involved). Tell your buildings insurer promptly.
Checking a property
Our postcode check shows whether soluble rock is mapped under a property at 1:625,000 scale, whether loose deposits cover it, and whether BGS records landslides, boreholes or mine plans nearby. For a purchase, a professional ground stability search uses more detailed BGS GeoSure soluble rocks data and, in coalfields, a mining report.