Myth busted: This is the REAL reason Norwich gets so many sinkholes

The sinkhole in March at Whistlefish Court is an extreme example of what can happen

Was the sinkhole in Whistlefish Court due to chalk mines beneath the city? Matthew Williams (inset) explains - Credit: Matthew Williams

For years gaping sinkholes yawning open across Norwich have been blamed on cavernous chalk mines buried beneath the city surface. 

However despite the blame frequently being placed on the mines, the caves are actually not the guilty party.

From the middle ages, through to the beginning of Second World War, Norwich was mined for chalk and flint and today many of the mines, believed to have been dug between the 12th and 18th centuries, still remain underneath the city.

The green space on Frere Road where is a sinkhole has appeared is popular with dogwalkers and childr

A sinkhole in Frere Road, Norwich - Credit: Archant

A geologist has now revealed the real reason why so many craters creep open in Norwich - clearing the besmirched reputation of the chalk quarries.

Geologist Matt Williams, 65, has explained that by building Norwich on notoriously unsteady material - sand - modern day city folk are now paying the price.

The 'rock star' said: “Norwich is largely built on just sand overlaying chalk. Neither are very strong and there are concentrated pockets of water running in and between those layers.

Whistlefish Court in Norwich where a sinkhole has oppened up. Picture: Danielle Booden

Whistlefish Court in Norwich where a sinkhole opened up - Credit: Archant

"But once Norwich started being known as the sinkhole capital it opened up all sorts of mythology with people thinking it was to do with the mines.

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"It's not collapsing into mines - the sand is just being washed away."

A bus which fell into a sinkhole on Earlham Road, Norwich in March 1988. Harrison Group Environmenta

A bus which fell into a sinkhole on Earlham Road, Norwich in March 1988. Harrison Group Environmental, which is based in the city, investigated the cause of the sinkhole. Picture: Archant archives - Credit: Archant

And like any city, Norwich is riddled with drains and water supplies which can burst within the layer of sand.

And Matt warned the city's current preoccupation with roadworks could cause even more issues: "When roads are dug up for any reason the trench it creates must be backfilled. 

"If it's not it will create pockets of empty space which sand then washes into and creates more issues later."

Past chalk mining areas in Norwich. Harford Hills. "A sandpot showing debris-flow and degradation of

Past chalk mining areas in Norwich. Harford Hills. "A sandpot showing debris-flow" - Credit: Archant Library

Warmer weather will spell yet more trouble: "This summer we could see more holes open up because road tarmac often bridges these holes.

"But when the tarmac gets hot it simply can't bridge that weak spot.

For eagle-eyed sinkhole spotters, he had a few tips on what to watch out for. 

The chalk mines below Norwich. Picture: Gavin Wilson

The chalk mines below Norwich. Picture: Gavin Wilson - Credit: Gavin Wilson

"You'll often see the start of a sinkhole as just a dip in the tarmac - particularly close to drains or sewers," the boffin explained. 

To find out more about the underground conditions Matt Williams has written a book called ‘Subterranean Norwich – The grain of the city’ which is available from city bookshops or from www.sctbooks.co.uk.   

Matt Williams has written a book about the ground beneath Norwich's feet called Subterranean Norwich

Matt Williams has written a book about the ground beneath Norwich's feet called Subterranean Norwich - The grain of the city. - Credit: Matt Williams

A short history of chalk mining in the Fine City

Chalk mined in Norwich and flint found out towards Thetford were two of the materials which were used to build walls and buildings folk still see today.

And while many of the chalk mines still exist, not all of them have been found.

Past chalk mining areas in Norwich. Rosary Road. "The main chamber showing relics of World war Two."

Past chalk mining areas in Norwich. Rosary Road. - Credit: Archant Library

No detailed maps of all the mines within the city boundary exist and thus a lot of independent research and exploring has been undertaken in attempt to uncover their exact locations. 

However the city council has asked people not to seek out the mines.

Many are also blocked up and others are inaccessible because they are on private land.  

The mines are dangerous and many are at risk of collapse.

The oxygen quality in the tunnels is also below safe levels.