The study of sinkholes has attracted considerable media attention since the tragic death of a man at Seffner near Tampa, Florida, on 1 March 2013 — Sinkhole swallows up Florida man Jeffrey Bush | BBC News
A sinkhole, that had formed beneath Mr Bush's house, 'swallowed' him when the house floor collapsed.
Later in March 2013, a golfer was injured when a sinkhole opened up on the fairway of an Illinois golf course.
Increased incidence of sinkholes and collaspse subsidence features:
An example of how ancient mine workings can lead to collapse subsidence.
‘Sinkhole’ in the middle of the M2: February 2014
The sustained period of wet weather is suspected to be the trigger for the recent spate of sinkholes and collapse subsidence features that have been reported in the south and south-east.
Dr Anthony Cooper, gives an account of the most recent sinkhole to appear in the Ripon area.
Report a sinkhole near you with our online form.
There are several different types of sinkhole — sometimes called dolines:
Some result from the surface dissolution of the soluble rock (solution sinkholes) — for example limestone rocks dissolve when attacked by rainfall or groundwater that is acidic.
Sinkholes also occur where a thin covering of loose superficial material such as sand, clay or soil covers the soluble rocks beneath. In this setting, the soil can be washed into solutionally widened fissures below, leading to the development of a cavity within the overlying material.
If the cover material is sandy, it will tend to gradually slump into the fissures, slowly creating a sinkhole over time (suffosion sinkhole).
However, if the material is more cohesive, like clay, then the cavity can grow quite large before suddenly collapsing; a process termed a 'drop out' sinkhole. It is these more spectacular collapses that sometimes hit the headlines.
In other cases, it is the gradual collapse of a cave passage at depth that can trigger a sinkhole.
The collapse can gradually propagate up through the overlying strata to cause subsidence at the surface (a 'collapse sinkhole'). These sometimes extend up into rocks that are not themselves prone to dissolution, creating a 'caprock sinkhole'.
These are common in parts of South Wales where sandstone rocks overlie cavernous limestone and in Ripon where sandstone and limestone overlie gypsum. Others may be buried by more recent deposits.
Some sinkholes are caused not by dissolution of limestone, but the erosion of weak unconsolidated material by flowing water. Loose material can removed by a process called ‘soil piping’, creating large voids within the sediment.
One of the most spectacular examples of this type of collapse is the event that occurred in May 2010 in Guatemala City. Here, cavities developed in weak, unconsolidated, volcanic deposits following a tropical storm. These then collapsed, creating a shaft approximately 100 m deep and 20 m wide.
Several things can trigger sinkholes. The simple process of gradual dissolution can cause a sinkhole to form at the surface.
However, other factors, including humans can induce sinkholes to form, such as:
Construction and development are also potential triggers. Modifying surface drainage or altering the loads imposed on the ground without adequate support can caused sinkholes to develop.
In some parts of the world, drought or groundwater abstraction can cause sinkholes by changing the level of the water-table. This removes the buoyant support water provides to a cavity. Draining these cavities can cause them to collapse.
Mining can be a factor in causing sinkholes, either by dewatering and lowering of the water-table, or by intercepting clay filled voids which subsequently collapse. Several sinkholes in Norwich have been caused by old chalk mines intercepting otherwise stable sediment-filled voids.
Areas prone to sinkhole formation occur throughout the UK, although most are relatively small or are in upland rural locations.
These include areas underlain by Carboniferous limestones, notably the Mendips, parts of Wales, the Peak District, and the northern Pennines including the Yorkshire Dales.
The Chalk is also susceptible, especially where it is covered by younger clay and sand deposits (the 'Clay-with Flints' and Palaeogene strata), notably in parts of Dorset, Hampshire and the Chilterns.
However, the most susceptible area in the UK is the Permian gypsum deposits of north-east England, particularly around Ripon.
Many large sinkholes have developed around Ripon, some of which have affected property and infrastructure. This is because gypsum is far more soluble than limestone, and thus dissolves more rapidly.
Sinkholes also occur over salt deposits, commonly in areas such as Cheshire where brine has been extracted making it difficult to separate naturally formed sinkholes from those created by man.
In Scotland, sinkholes are generally rare except in parts of Assynt underlain by the Cambrian Durness limestone.
The hazards associated with sinkholes can be mitigated by appropriate planning, good site investigation (with geophysics and boreholes), appropriate design and proper maintenance of infrastructure such as drains and services.
Care is required when installing any structures that could affect the local groundwater flow or groundwater levels including soakaways (sustainable drainage systems or SUDs) and open loop ground source heat pumps; in some places on soluble rocks these may be impractical.
The BGS provides information regarding the susceptibility of the ground to dissolution and mining. This does not include information on the associated likelihood. The likelihood of occurrence is also linked to the history of the development of a site, for example many sites will have been remediated. Additionally, the distribution of medieval workings is poorly documented and the available information on mines is limited.
If you wish to know whether your area is prone to sinkholes, you can find out by visiting our Caves, subsidence and soluble rocks pages or by using GeoSure data to access information on these geological hazards.
The methodology behind the development of the GeoSure dissolution hazard layer is outlined in the document below:
Farrant, A R, and Cooper, A. 2008 Karst geohazards in the UK: the use of digital data for hazard management. Quarterly Journal of Engineering Geology and Hydrogeology, 41 (3), 339–356.