A small hole around the size of a dinner plate was first reported beside the Inland Coast Path on Bronkham Hill, West Dorset, in February this year.
It was investigated by Dorset Council’s Ranger Team and then geologists, who found that the small hole was covering a chasm that has the potential to be up to 30 metres wide and 15 metres deep. A barrier was put up and the restricted byway was temporarily closed.
That small surface hole has since opened up to a huge sink hole. While it may look alarming, the hole does appear to be stable, according to assessments.
John Sellgren, Executive Director for Place at Dorset Council said: “When this hole was first reported we took action as we knew it could indicate a chasm of unknown depth. Safety precautions were taken, and an investigation was carried out.
“I am happy to report that the sink hole now appears stable and the National Trail is open. Sink holes occur naturally, but our advice is always take care and if you have concerns report them to Dorset Council.
Sink holes are rare in Dorset, but have occurred throughout history at BronkhamHill, which is north-east of Portesham. They occur naturally when the surface layer of land collapses into ancient hollows formed during the last ice age. This particular sink hole is believed to have been caused during the last major glacial period where meltwater dissolved the rocks below.
At Bronkham Hill, which is part of the Dorset Area of Outstanding Natural Beauty (AONB), rainwater seeps through the surface flint and gravel and dissolves the porous chalk beneath.
Around 200 steep-grass lined pits can be found nearby, known as ‘elliptical dolines’. These are sink holes of the past which have now grassed over.