Authorities burying head in sand over Ripon sinkhole collapses, says geologist

FORMER University of Sunderland lecturer Ross Nicolson has returned to Ripon, a place he used to bring his students to, to examine sinkholes.

"Ripon is now known as the sinkhole capital of Britain", he says as he points out a plethora of buildings that have moved and landforms created by dissolving underground gypsum deposits.

We're standing in Magdalens Road, where seven houses were evacuated earlier this month after a 20m-wide and 9m-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.

The British Geological Survey (BGS) says catastrophic ground collapses, yards from where another sinkhole appeared beneath a 100-year-old building in 2014, are "not unusual events for the Ripon area".

The city's sinkholes, which are thought to have inspired Lewis Carroll to write in 1865 about Alice tumbling down a hole in Alice's Adventure in Wonderland. It is said in 1860, a clergyman colleague of the author's 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 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."

Engineering geologist Ross Nicolson points towards a historic sinkhole off Magdalens Road, Ripon

For craters to suddenly appear, a similarly large void, cavity or cavern must have been forming beneath the surface for a long time, but following the latest collapse The City of Ripon Trust warned probes to detect gypsum dissolution could create drains, activating 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 70m 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 met with their full approval, before being used 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."