Torrential rain over the festive period may have caused a 130ft-deep and 160ft-wide sink-hole to form in the Peak District.
The growing hole that was part of the Nether Slaters Mine in Foolow, caved in overnight after water eroded the earth underneath, causing the whole area to collapse.
Caver Mark Noble, 58, from Eyam, said he saw the hole during a walk on Christmas Day, but believes the land began to fall a couple of days before.
He said: “I heard about it in the pub on Christmas Eve so had a walk up there the next day.
“It pretty much appeared over night, in a couple of hours.”
Mark said he has explored the caves at Foolow in the past as huge cavities were left in the area from an old lead mine.
He added: “It’s a massive hole and it’s getting bigger all the time.
“It’s probably increased by about ten per cent since it opened up.”
Mark said: “It is quite interesting but there are two other similar large holes that appeared about half a mile away from this one in the 1970s. It’s not uncommon.”
Electrical engineers assessed the site on Monday to decide how to re-route electric cables, after two poles were left dangling either side of the gaping hole.
Although there has not been any official reason for the ground collapsing yet, according to the British Geological Society, mining can be a factor in causing sinkholes.
The process can cause the ground to fall in either by de-watering and lowering the water-table, or by intercepting clay filled voids which go on to collapse.
The sinkhole lies over old mine workings which date back to 1705 and the area has been worked for lead and fluorspar since then.
Mark said ground water or collapse of ancient supports can cause the ground to collapse.
He added: “The area is currently being worked at much greater depth, from Milldam Mine in Great Hucklow, but the collapse does not appear to have affected operations there.”
Most areas in the UK susceptible to sink-holes are relatively small or are in upland rural locations such as the Peak District.