Why sinkholes are opening up across the UK
For several days last week, AFC Wimbledon found itself unexpectedly in the front pages after staff arriving at the ground found a whole corner of the otherwise pristine pitch resembling a golf course. Sandy bunkers and grassy mounds had appeared after a weekend of torrential rain. It looked as if some burrowing animals had taken an interest in the south London side. Were the Wombles themselves to blame, at least one wag joked on social media.
More than a week later, it remained unclear precisely what had caused the Wimbledon “sinkhole”, as the ruptures were initially described. The rain was surely a factor in making the ground bubble and shift; tankers had to be called in to pump more than 100,000 litres of water out of Plough Lane, where the players’ tunnel and team shop had also been flooded after the nearby river Wandle burst its banks.
As earth movers carried out repairs and home games were postponed, the Dons’ supporters dug deep. One fan, Graham Stacey, raised almost £123,000 on a fundraising site before the club politely asked him to pause the appeal, which had already done enough to cover the excess for its insurance claim.
Britain was once again grappling with the impact of a problem that inspires fear and fascination. If we take for granted the stability of the ground we have shaped beneath our feet, then sinkholes and other earthly depressions and fissures are increasingly reminding us that we ignore the underworld at our peril.
And true sinkholes, which at their largest can swallow entire buildings and vehicles, are becoming more common in this country, partly as a result of extreme rainfall that scientists attribute to climate change. With a kind of cruel circularity, these deluges are in many cases weakening the geophysical scars of our industrialisation, infiltrating and weighing down on old mines and brickworks.
“I’m just surprised more people haven’t been killed,” says Mark Hudson, the managing director of Geoterra, a Cheshire-based land surveying firm where sinkhole-related inquiries have tripled in the past decade. “But it is going to happen, because the problem tends to be that you just don’t know where holes are going to appear.”
Regions built on layers of soluble rock such as chalk, gypsum or limestone are particularly vulnerable to erosion by groundwater. Heavy rain can also flush sediment through the vertical “dissolution pipes” created by this erosion, opening up space ready to swallow up the surface – and whatever sits above it.
“But I’d say the vast majority of sinkhole collapses in England have been anthropogenic,” that is, originating in human activity, says Andrew Farrant, a geologist at the British Geological Survey, which has a busy “shallow geohazards” team. Farrant says rain and poor drainage can cause the collapse of former mines, shafts, wells, sewers and even air raid shelters. In some cases, closed mines were poorly capped, sometimes with earth piled up on timber that was liable to rot and give way.
“There’s definitely a link between heavy rainfall and the likely occurrence of sinkholes, but we don’t know how many occur, partly because many just don’t get recorded,” adds Farrant, who says cycles of drought and heavy rain made worse by climate change can trigger the kind of movement that creates sinkholes. A warming atmosphere is capable of holding more moisture, leading to heavier downpours. Moreover, there is evidence that global heating is affecting the jet stream in a way that may be resulting in a “stalling” phenomenon, causing rainstorms to get stuck and dump larger quantities of rain on the same region.
Where holes open up in built-up areas, their disturbance extends far beyond the ground itself, tapping into primal fears of what lies beneath. Farrant says the last sinkhole deaths he is aware of happened in 1936, when a Mr Thomas Hall and his wife were swallowed up, along with most of their house, by a hole eight metres wide and almost five metres deep in Norwich, much of which is built on sandy soil above centuries-old chalk and flint mines.
More recently in Norwich, in 1988, the number 26 bus fell into another chalk-mine sinkhole in the city centre. The bus driver was able to lead passengers to safety, giving Cadbury’s the ethical leeway to run a newspaper ad to promote one of its chocolate bars. It showed a photo of the half-buried bus above the words: “Nothing fills a hole like a Double Decker.”
When holes appear these days, Hudson, who started his career as a coal mine surveyor, tends to be the specialist who local authorities or landowners call on to assess the damage. One of the most startling jobs he has done recently brought him to the affluent edge of Wooburn, a village near Marlow in Buckinghamshire. A hole six metres across had appeared on Sappers Field, a small common fringed by trees and huge houses. Much of a children’s playground had fallen into the hole, which opened up two metres from the bottom of a metal slide.
After advising the council to extend the exclusion zone around the hole, Hudson gingerly climbed on to a cherry picker basket and positioned it over the opening. He could see the bottom of the hole, about 10 metres down. “But then there was this perfectly circular hole about one and a half metres across,” he recalls. Hudson lowered a video camera on a rope into the hole within the hole. “And it just went down, down, down… 35 metres later, it hit the bottom.”
Hudson then lowered in a laser scanner to create a 3D image of the vast hollow, revealing its stretched, bell-like shape. The hole was indeed a rudimentary 19th-century “bell pit”. Miners dug these narrow shafts to the required depth and then began extracting rock or clay outwards, as far into the depths as they dared, before leaving via the shaft and capping the pit.
“Wasn’t it lucky that there were no kids on the playing field or the swings when it collapsed?,” says Hudson, who had scanned an earlier hole on the same field in 2020. He says surveys then revealed further anomalies of concern, yet the council had only just filled the first hole and reopened the field when the second hole opened up.
“It really brought home the reality of sinkholes to see the children’s slide pretty much ending in a 35-metre-deep hole,” says James Mortimer, a parish councillor in Wooburn, who also happens to be a geotechnical engineer who has studied sinkholes. He says the local resident’s association had been planning a picnic to celebrate the field’s reopening when the playground disappeared.
A spokesperson for Buckinghamshire Council, which owns the field, tells me that surveys after the first hole did not indicate “any further significant issues” and that the capping above the shaft inside the second hole, which has now been filled, did not show up in those earlier scans. “A more detailed geotechnical survey has been undertaken that appears to indicate that there might potentially be several more man-made capped voids,” the council says. New surveys are ongoing, it adds, and the field remains shut. Meanwhile work on both holes has so far cost the council more than £600,000.
More broadly, Hudson thinks ignorance of often unmapped earthworks combine with a fear of the huge consequences and costs of facing up to and dealing with holes to result in inaction and delay, often leaving residents in the lurch as local authorities, landowners and insurers fight over what can be astronomical bills.
Mat Pritchard has lived for almost 30 years in Ripon in North Yorkshire. When he moved in, he had no idea that the cathedral city has a reputation as Britain’s sinkhole capital. Water is slowly dissolving large underground deposits of gypsum, creating hollows that in some cases aren’t strong enough to support the city above.
In recent years, houses and a branch of Sainsbury’s have had to be evacuated where holes have appeared. There have been at least 30 collapses in the city in the past 150 years, according to the Geological Society.
In 2000, Pritchard, 55, bought a two-bedroom flat for £50,000 in a newbuild development yards from Ripon Cathedral, latterly using it as a home for his father, who’s now in his eighties. Cracks started to appear in the building in 2008. They grew only slowly at first, until rapid growth triggered a comprehensive survey in 2020.
“Up until that point, the civil engineers were saying, ‘it’s still sound, you’ve just got a bit of cracking’,” Pritchard recalls. “But then it got to the point, in 2020, when they said, ‘Not only do I think you should get everyone out of here now, but I also don’t want to go into that building anymore’.”
Residents of four flats in the affected building moved out within weeks, straining already fraught relations between them and their insurance company over who should pay out, and accusations of shoddy work despite what Pritchard says was clear evidence that the block sat above gypsum.
Pritchard, who runs a research consultancy in the aid sector, represented residents in a fight that caused him huge stress and, he says, contributed to the breakdown of his marriage. “I can’t tell you the number of evenings and weekends I spent working on this,” he tells me. “That flat was a big chunk of our retirement planning and the stress of dealing with this was a significant weight on our marriage. If you put a heavy load over a weak bridge, what’s going to happen?”
Pritchard, who rents a home in Ripon and has two children at university, eventually ran out of options. In March of last year, bulldozers demolished the whole block, leaving a void that he says remains empty. He was one of 29 residents at the whole property, which includes unaffected buildings, who had to pay an estimated £180,000 in total for work including demolition. “Every time I drive past it, I can still feel the remnants of the bitterness and stress,” he says. “It felt like part of my future had been erased.”
He thinks a culture of “agreed silence” hangs above areas of Britain that are vulnerable to sinkholes, where in some cases the solutions are hard to fathom. “Geologically, the best thing for Ripon would be to pick it up and move it about two miles west where there isn’t any gypsum,” he says. “But of course you can’t do that.”
British sinkholes tend to be relatively modest in size but big enough to cause problems and risk lives. Farrant remembers a spate of sinkholes in 2014, when record rains weakened ground all over the country. In High Wycombe, Liz and Phil Conran’s 19-year-old daughter Zoe was hysterical after waking up one morning to find that her prized VW Lupo had fallen into a 4.5-metre hole in their driveway. Auto Trader later paid for a replacement.
But there are warning signs in other countries, where tropical rains and more extreme weather are creating conditions ripe for larger holes. In August, a pair of shoes were the only trace of an Indian tourist who vanished into a hole on a pavement in Kuala Lumpur in Malaysia.
In 2022, heavy rain may have hastened the sudden opening of a geothermal hole in Rotorua in New Zealand, which left an Australian woman in hospital with serious injuries.
In Naples, rescue dogs searched for victims of a giant sinkhole that swallowed an entire hospital car park but no injuries were reported. And there have been multiple deaths in Guatemala City, where holes the size of city blocks have opened up after tropical storms.
This week, AFC Wimbledon were heading to Newcastle to play their postponed Carabao Cup third-round tie at St James’s Park after their opponents offered to host the match. Their ground staff may want to seek advice from the owners of Gordon Moore Park in Alton, Illinois. In June, a 30-metre wide and nine-metre deep sinkhole took out the centre of a football training ground.
The Alton parks and recreation director, Michael Haynes, told a local news station that the collapse “looks like something out of a movie, right? It looks like a bomb went off.”
When AFC Wimbledon’s managing director James Woodroof first saw images of the damage to his pitch, he assumed they had been made by artificial intelligence. But, all over Britain, as extreme weather puts a strain on our fragile subterranean world, such scenes are becoming all too real.