Ripon's sinkholes: Experts have their say on what can cause them in our city
Ripon has been informally described as "the sinkhole capital of the UK," and ever since a new sinkhole appeared behind Sainsbury's yesterday, readers have been wondering just how many more we are going to see, and how bad it could get.
The Ripon Gazette contacted the British Geological Survey to find out more about what can contribute to a sinkhole's formation in our city.
Dr Vanessa J Banks of the British Geological Survey, said: "The process of sinkhole occurrence in the Ripon area is largely attributable to the dissolution of gypsum in the Permian rocks that underlie the city. The natural rate of occurrence of these features appears to be in the order of one every three to five years.
"However, the ability of water to dissolve gypsum depends on how much gypsum is already dissolved in the water such that fast flow paths of fresh water will dissolve gypsum more readily than slowly moving groundwater that is partially saturated with gypsum.
"As a consequence, the ground conditions in Ripon are particularly vulnerable to increased volumes of infiltrating water. An increase in the rate of sinkhole formation may be a natural occurrence due to intense rainfall, particularly in conjunction with any desiccation and cracking of the ground facilitating water ingress; or a consequence of any damage to any water bearing services.
"Inflexible service pipes are very susceptible to fracture as a consequence of any ground movement. Extremes of weather can result in ground movement and shrinkage and therefore this may have a direct or indirect consequence in terms of the rate of sinkhole formation."