Around 16,000 years ago, the area surrounding Burn O'Vat was covered by a glacial ice sheet. As the area warmed everywhere 14 000 years ago, the ice sheet began to melt, resulting in a torrent of meltwater that carried with it debris previously caught up in the glacial ice. This debris, consisting of rocks and boulders, is thought likely to be the most important component of the formation of Burn O'Vat.
It is believed that a rock from the meltwater stream lodged in a small hollow on the river bed, causing the meltwater to flow around it in a spiraling motion. This spiraling motion caused the bed underneath the rock to erode over a long time, creating a pothole feature.
Around 13 500 years ago the volume of meltwater decreased to such a level that the stream began to deposit more than it was eroding. This change resulted in the deposition of sand and gravel into the bottom of the pothole. This sediment extends down around 5–7 meters, below the current ground level, though no-one can be sure of the actual value.
The pothole, known locally as 'The Vat', measures 18 meters across and 13 metres high, from the present ground level.
Approximately 12 000 years ago, the vat's entrance was exposed when the rock in front of it was undercut by the same stream that formed the vat, albeit in the form of a waterfall.