Ice Age Rivers
During the last one million years (the Pleistocene Epoch) Ice Ages gripped most of Britain. During the cold Glacial phases, sheets of ice up to two miles thick reached as far south as the Mendip Hills. During the warmer interglacial periods torrents of water were released as the ice melted and escaped south along existing river beds.
Each torrent of water swept along with it boulders and gravel which scoured out a deep channel, eventually cutting a Gorge 400 ft deep and 3 miles long out of the Hill.
The Carboniferous Limestone rock of which the Mendip Hills is formed contains many cracks which also allowed the river to work its way underground, enlarging the cracks into caves.
Courtesy www.cheddarcaves.co.uk