The science of sinkholes: Why does the ground open up?
- Credit: Adrian Judd © Archant
They disrupt to traffic, damage property and even force businesses to close.
And as recent incidents in Sheringham's High Street and the A47 in Lowestoft show, we're no closer to putting a lid on the problem of sinkholes.
But what causes this phenomenon, which once famously swallowed a double-decker bus on a Norwich street?
Professor Julian Andrews from the University of East Anglia's school of environmental science said East Anglia was prone to two main types of sinkholes: smaller ones under roads, and bigger, naturally occurring sinkholes which occur where chalk bedrock is near the surface.
Prof Andrews, 59, said 'natural' sinkholes could be tens of metres across and could cause houses to collapse.
He said: "Examples include Kett's Hill in Norwich.
"Chalk is a type of limestone that dissolves in rainwater, the water flows into fissues in the chalk and gradually enlarges them until a hole is formed or the top of the chalk collapses."
MORE: Sheringham sinkhole tee shirts set to go on sale as workers continue underground surveysProf Andrews said smaller sinkholes, including those in Sheringham and Lowestoft, were usually caused by running water dissolving the ground beneath the surface, creating a cavity with only a thin layer on top, which then collapses.
- 1 'Once in a lifetime catch' - man lands monster fish in Norfolk
- 2 Doctors baffled by teenager's horrific long Covid symptoms
- 3 Norfolk man amongst UK's 12 most wanted
- 4 Norfolk village named among poshest places to live in the UK
- 5 Pub near Dereham has its first winners of steak-eating challenge
- 6 Couple explores Norfolk homes in Escape to the Country
- 7 Tucked-away house in same family for over 100 years up for sale
- 8 MAPPED: Where thousands of homes could be built in north Norfolk
- 9 Drunk student crashed into hotel wall after drinking tequilas
- 10 'Fantastic, loving, cheeky' 19-year-old killed in motorbike crash
He said: "In Lowestoft the chalk is deep below the surface, so in this case it is probably water from a leaking pipe or sewer that is undermining the made-ground below the road. In the case of Sheringham the chalk is not so far below the surface - in fact you can see it on the beach at low tide - so it could be disturbance of the made ground but with chalk dissolving below that."
Although it may seem like our region gets more thank its fair share of sinkholes in roads, Prof Andrews said they could happen anywhere the 'made' ground was poorly prepared or not well packed.
He said: "Sewers and water pipes are routed under roads, so when they leak we have the problem. The picture of the Sheringham sinkhole shows it directly in line with a manhole cover."
MORE: 'This is a complex investigation': A47 sinkhole repairs continuingAnglian Water teams are still hard at work repairing both the Sheringham and Lowestoft sinkholes - with diversions in place around the affected roads.
Sinkholes: They keep happening
East Anglia has a long history of sinkholes, but the most famous is the one that appeared in Earlham Road in 1988.
That sinkhole, which occurred after a medieval chalk mine collapsed, swallowed a double-decker bus and made headlines around the world.
The driver and passenger managed to scramble off before more damage was caused.
But that was by no means the biggest sinkhole the city has suffered.
Merton Road resident Thomas Hall and his wife were killed when an 80ft-deep sinkhole swallowed theirs and two other homes on May 11, 1936.
In 2016 a six-metre-deep (20ft) sinkhole large enough to swallow a small car appeared in Plumstead Road, near Kett's Hill.
And in the same year a garden in Thetford was destroyed by a sinkhole.
That hole - which was 15ft wide and about 8ft deep - caused two walls to collapse and swallowed a double garden gate.