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Porth yr Ogof in Waterfall Country
Brecon Beacons Geology and Cave
This southern edge of the Brecon Beacons National Park contains a belt of carboniferous limestone wedged between Old Red sandstone to the north and the Millstone Grit containing coal deposits to the south. One of the characteristics of carboniferous limestone is that it is susceptible to the action of slightly acidic water. Rain falling in this locality absorbs carbon dioxide from the air thus creating a mild solution of carbonic acid. As this slightly acidic water passes through the naturally occurring cracks and fissures in the carboniferous limestone over geological time it has created the extensive cave systems found along this southern edge of the Brecon Beacons National Park.
Safety and Access from the Car Park:
Brecon Beacons National Park signs warn of the dangers of:
Porth yr Ogof is the largest cave entrance in Wales and one of the largest anywhere in the United Kingdom. It is nearly 20 m wide and some 3 m high.
The cave was at onetime referred to as the "White Horse Cave". The name is derives from Calcite streaks just inside the cave which resemble the head of a horse. Calcite is a crystalline form of calcium carbonate in the same way that ice is a crystalline form of water.
On the surface to the south of the cave entrance (below the minor road) it is possible to walk (albeit with some difficulty) along the original riverbed of the Afon Mellte prior to its collapse upstream and submergence in the Porth yr Ogof cave system.
Caving and Safety:
In periods of rainfall the cave entrance and the passageways can fill with water very quickly.
A Mountain Hut Production
Keith Rapado © 2002 All rights reserved.
Revised: 23 June 2009 This non profit making website is independent
(of the Brecon Beacons National Park Authority) & supports National Park aims regarding recreation, conservation & the local economy.
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