A leading engineering geologist has called for the authorities to stop burying their head in the sand over sinkhole collapses in Ripon before tragedy strikes. Stuart Minting reports

"RIPON is now known as the sinkhole capital of Britain," says geologist Ross Nicholson, standing in Magdalen's Road and pointing to the numerous buildings which have moved because of dissolving underground gypsum deposits. Earlier this month, seven houses in the street were evacuated earlier after a 20 metre wide and nine metre deep sinkhole opened up in gardens, which left 74-year-old resident Frances O'Neill clinging to her washing line pole to avoid falling into the crater.

It is an area Mr Nicolson knows well as when he lectured at Sunderland university, he brought his students to examine the sinkholes, and the British Geological Survey (BGS) says the catastrophic ground collapses are "not unusual events for the Ripon area".

In fact, the city's sinkholes are thought to have inspired Lewis Carroll, whose father was a residentiary canon at the cathedral, to write in 1865 about Alice tumbling down a hole in Alice's Adventure in Wonderland. It is said that in 1860, a clergyman colleague of his father narrowly avoided a sinkhole collapse as he walked along the banks of the River Ure, a stone's throw from Magdalen's Road.

The highly dissolvable nature of permian gypsum deposits upon which many Ripon properties stand has been extensively documented, with the BGS last week describing it as one of the UK's most susceptible areas for sinkholes.

Mr Nicolson, principal geotechnical consultant with Stokesley-based firm Geoinvestigate, says investigatory drilling work has not been done to pinpoint the areas most at risk, but with technology advances "it is no longer acceptable to sit on our hands and wait for the next sinkhole collapse to occur".

"We know they are going to continue collapsing and with climate change and more regularly inundations of rain they are likely to be more frequent," he says. "If we carry on playing Russian Roulette with the sinkhole crisis in Ripon there could be serious injury or even loss of life."

For craters to suddenly appear on the surface, a large void, cavity or cavern must have been forming underground for a long time, but following the latest collapse, the City of Ripon Trust has warned that putting down probes to detect gypsum dissolution could create drains which would then activate more sinkholes.

Mr Nicolson says his firm's "relatively cheap" 45mm diameter Microdrill, which was launched last year, would not lead to significant amounts of water going beneath the surface and could detect holes forming 70 metres underground. He describes it as the "next best thing you can get to completely safe".

"In my opinion we are not doing enough drilling because we don’t really want to know how serious and extensive the problem is in Ripon," he says. "This is perhaps understandable in some ways given that the outcome is likely to raise very serious concerns with regard to public safety, property blight, insurance cover and ultimately liability and cost."

He says Microdrill was successfully used by the UK Coal Authority last year and also by a Hertfordshire council to investigate a chalk sinkhole outside sheltered housing.

"Given the especially serious and unique nature of the risks posed to the public in Ripon, central and local government and insurers have a duty of care to thoroughly investigate and establish the full extent of the sinkhole problem in the city as soon as possible," says Mr Nicolson.

"It’s similar to a molehill problem. We don’t know exactly where the next hole is going to pop-up, but as surely as night follows day more are going to appear unless drastic action is taken to prevent them or in the case of Ripon’s sinkholes to better predict their occurrence and take the necessary action. It is a question of public safety and locating the high-risk properties while there is time before a catastrophic collapse."

Mr Nicolson says authorities should fund a Microdrill trial in the city, and if it is successful, drill every property in Ripon, starting with the area most at risk.

He adds: "If my family lived in Ripon I would rather have drilling done than wake during the night to find out that large hole had collapsed beneath my house or that my garden had disappeared where the day before my kids had been playing during school holidays – and this could have been avoided by drilling."