Matthew Budd Radley College – OX14 2HR CHEDDAR GORGE

Matthew Budd
Radley College – OX14 2HR
My visit to Cheddar Gorge enabled me to get to grips with the geological structures that are usually
only seen on computer screens or in books. I went to Cheddar Gorge to broaden my knowledge of
these geological structures.
I learnt that the entire area is underlain with Burrington Oolite, Black Rock slate and Clifton Down
Limestone from the Carboniferous. This rock contained ooliths and fossil debris, either broken or
disarticulated. This is all on top of Old Red Sandstone. There is even evidence for Variscan orogeny
due to the sheared rock and cleaved shales. Weathering of these rocks and strata has led to the
formation of immature calcareous soils.
Whilst at the site I learnt that the gorge itself is 137m deep in places and was formed by meltwater
floods during the periglacial periods over a time period of 1.2million years. During the ice ages the
caves that formed due to the erosive power of the meltwater were filled with ice and mud which
made the limestone impermeable. Therefore, when the glaciers melted, the water could not
permeate into the limestone and drain away but became surface run-off which, in turn, carved out
the gorge. In modern-day terms this has led to multiple floods such as the Great Flood of 1968 which
washed boulders down into the gorge, damaging the buildings there and washing away cars. In 2012
the road at the bottom of the gorge was closed for several weeks due to damage of the road surface
due to extensive flooding.
When Somerset was in a warmer period, the mud and ice would melt and cause the limestone to
become permeable again. The water would flow underground and began to carve out the caves and
left the gorge dry. Now the river runs under much of the gorge, only emerging in the lower part from
Gough’s Cave (above).
Photograph taken: Spring 2012