A large sinkhole opened up on a residential street in Merthyr Tydfil on Sunday (December 1).

The sinkhole - located on a residential street in Nant Morlais, Pant - is several metres deep and spans the entire pavement and some of the road on a . 

It is unknown (at the time of writing) what caused the sinkhole to develop and people are being told to avoid the area.

How do sinkholes form?

Sinkholes are usually formed by "the natural erosion or gradual removal of slightly soluble carbonate bedrock", according to e.surv Chartered Surveyors.

This is caused by acidic rain gradually filtering through and dissolving the bedrock or the inward collapse of a cave roof.

e.surv added that Sinkholes are most common where the rock below the surface is:

  • Limestone
  • Gypsum or other carbonate rock
  • Other soluble rocks (including sandstone or quartzite)

This is because the rock can be dissolved naturally by circulating groundwater or acidic rain.

Do you know how sinkholes form?Do you know how sinkholes form? (Image: Eye In The Sky) e.surv continued: "As the rock dissolves, spaces and caves develop underground.

"Groundwater may dissolve the carbonates that hold the sandstone particles together and then carry away the free particles, gradually forming a void.

"These sinkholes can be dramatic because the surface land usually stays intact until there is not enough support then a sudden collapse at the surface can occur sometimes without warning."

Prolonged flooding and wet weather is said to be major factors in speeding up the creation of a sinkhole.

What triggers a sinkhole?

Sinkholes can occur rapidly and without warning anywhere "specific geological conditions exist", the chartered surveying experts explain.

While gradual erosion can cause a sinkhole, there are several factors that can trigger a collapse including:

  • Heavy rain or surface flooding
  • Leaking drainage pipes
  • Burst water mains or irrigation systems
  • Emptying a swimming pool
  • Building works
  • Past mining operations

When do you need planning permission?

e.surv added: "Sinkhole collapse can be very sudden, taking only a few seconds to a gradual inward slump over time."

Mining operations combined with bad weather have caused incidents in south Wales in the past.

Back in February 2020, unprecedented rainfall in Storm Dennis caused a landslip on the Llanwonno hillside.

While just last week torrential rain from Storm Bert led to a coal tip landslide in the former mining community of Cwmtillery, Blaenau Gwent.

These incidents follow on from the Aberfan disaster back in 1966.

How to spot a sinkhole?

"Anticipating the occurrence of a sinkhole collapse is not easy and there may be little surface evidence of its existence," the experts at e.surv said.

However, the primary indicator when looking out for sinkholes is location.

e.surv explains: "Sinkholes predominantly occur in locations where specific geological conditions exist and so the likelihood can be reasonably anticipated in areas where there is a history of previous sinkholes."

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Clues to indicate the possible existence of a sinkhole include:

  • External depressions in the ground level
  • Slumped or leaning trees, telephone poles, fences or road signs
  • Any obvious structural movement

If you think there may be a sinkhole near you, you can contact your local council.