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The science of sinkholes: Why does the ground open up?

PUBLISHED: 12:55 08 June 2019 | UPDATED: 15:51 09 June 2019

The day a bus fell down a hole in Earlham Road in Norwich - 3rd March 1988.
 Photo: Adrian Judd

The day a bus fell down a hole in Earlham Road in Norwich - 3rd March 1988. Photo: Adrian Judd

Archant

They disrupt to traffic, damage property and even force businesses to close.

Julian Andrews, professor of geology at the University of East Anglia. Picture: Supplied by Julian AndrewsJulian Andrews, professor of geology at the University of East Anglia. Picture: Supplied by Julian Andrews

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.

A bus which fell into a sinkhole on Earlham Road, Norwich in March 1988. Picture: Archant archivesA bus which fell into a sinkhole on Earlham Road, Norwich in March 1988. Picture: Archant archives

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 surveys

Prof 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.

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."

Terry Butler, owner of Crofters Restaurant, has had to close due to the sinkhole which opened up in the High Street of Sheringham. Picture: STUART ANDERSONTerry Butler, owner of Crofters Restaurant, has had to close due to the sinkhole which opened up in the High Street of Sheringham. Picture: STUART ANDERSON

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 continuing

Anglian 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

Workers inpsecting the sinkhole in Sheringham High Street. Picture: STEPH MENZIESWorkers inpsecting the sinkhole in Sheringham High Street. Picture: STEPH MENZIES

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.

Anglian Water are continuing with work to repair the sinkhole which opened up on the northbound carriageway of the A47 Bascule Bridge road at the junction between Station Square and Commercial Road in Lowestoft. Picture: Mick HowesAnglian Water are continuing with work to repair the sinkhole which opened up on the northbound carriageway of the A47 Bascule Bridge road at the junction between Station Square and Commercial Road in Lowestoft. Picture: Mick Howes

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.

Sarah and Jamie Clare at the site of the sinkhole which damaged their car on Rouen Road in Norwich in March 2018. Picture: DENISE BRADLEYSarah and Jamie Clare at the site of the sinkhole which damaged their car on Rouen Road in Norwich in March 2018. Picture: DENISE BRADLEY

The car stuck in a sink hole on Rouen Road, Norwich. Photo: ArchantThe car stuck in a sink hole on Rouen Road, Norwich. Photo: Archant

A sinkhole in Plumstead Road, Norwich, in 2016. Picture: Simon FinlayA sinkhole in Plumstead Road, Norwich, in 2016. Picture: Simon Finlay

A sinkhole in Spar Road, Norwich, in 2018. Picture: DENISE BRADLEYA sinkhole in Spar Road, Norwich, in 2018. Picture: DENISE BRADLEY

A sinkhole in Silver Road, Norwich, in 2016. Picture: DENISE BRADLEYA sinkhole in Silver Road, Norwich, in 2016. Picture: DENISE BRADLEY

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