An enormous sinkhole opened in the middle of a busy high street this morning, causing havoc for many people – but what is a sinkhole?
A cordon is in place on Godstone High Street and the road has been closed between Oxted Road and Bletchingley Road. A number of buildings have been evacuated and some homes are currently without water with businesses also impacted.
The problem afflicts several places across the UK, but what causes sinkholes? Weather and climate change and human activity are thought to be some of the causes of the problem, with many appearing at this time of the year when freezing temperatures hit.
The British Geological Survey says: “There are several different types of sinkhole, caused by different processes, including dissolution, collapse and erosion. Some sinkholes result from the surface dissolution of soluble rock. For example, limestone rocks dissolve when attacked by rainfall or groundwater that is acidic. Collapse dolines occur as consequences of the gradual collapse of a cave passage at depth.
“The collapse may gradually propagate up through the overlying strata to cause subsidence at the surface (a ‘collapse sinkhole’). These sometimes extend up into rocks which are not themselves prone to dissolution, creating a ‘caprock sinkhole’. Sinkholes of this type are common in parts of South Wales where sandstone rocks overlie cavernous limestone and in Ripon, Yorkshire, where sandstone and limestone overlie gypsum. Others may be buried by more recent deposits.
“Sinkholes can also form as a result of both dissolution and subsequent collapse. Where a thin covering of loose, superficial material (such as sand, clay or soil) covers the soluble rocks beneath, the soil can be washed into solutionally widened fissures or cavities below. If the cover material is sandy, it will tend to gradually slump into the fissures, slowly creating a sinkhole over time. However, if the material is more cohesive, like clay, then the cavity can grow quite large before suddenly collapsing.”
Sinkholes tend to appear next to buildings and other human constructions where the water is more concentrated. For example, when water drains off a roof. Some sinkholes are caused by the erosion of weak, unconsolidated material by flowing water.
The sinkhole that appeared in Godstone today is estimated to be at least 19m (62ft) long and about 3m (10ft) wide. SES Water said in a statement at 12.50am on Tuesday that it was aware of a burst water main pipe on Godstone High Street. In an update, a spokesperson said that repairs were still taking place – and confirmed that the burst had “impacted water supplies to homes in the area”.
Get email updates from our environment editor on green issues and actions you can take