Porth yr Ogof

The main river entrance to Porth yr Ogof cave

Porth yr Ogof is a cave located near the village of Ystradfellte, near the southern boundary of the Brecon Beacons National Park in Wales. In 1998 the cave's passageways had been measured as over 2.25 km in length. Among the cave's fifteen entrances is the largest cave entrance in Wales and one of the largest in the UK standing at nearly 20m wide and 8m tall^[1] (but many of those entrances are only accessible to cave divers). The cave was used as a show cave many years ago, but it does not have the attractions of more decorated caves such as Dan yr Ogof, and so today the cave is more often used to introduce people to the enjoyment of the exploration of caves.

Inside the cave

Entry to Porth yr Ogof is most often made through the wide Main Entrance, either using a dry ledge on the left or by wading through the knee-deep river to the centre and right. Cavers are presented various challenges inside, including The Wormhole (a curving crawl tube on the right wall of the Main Entrance), The Letterbox (a rectangular space in the passage) and The Creek, home to Death Ledge on its nearside wall. There are also two features named the Washing Machine - both feature large expanses of water.

Porth yr Ogof is now uncommercialised, and is also invaluable as a learning resource for caving. Along with the other attractions in the cave, two short potholes are easily accessible by amateur potholers. The cave is generally wet, however; White Horse Pool, named so because of the shape of the calcite deposit on the back wall, is several metres in depth despite the shallowness of the edges, and there are many sumps (completely flooded passageways), the majority of which exist in the portions of the cave north of the Trademan's Entrance.

Deaths

There have been eleven deaths at Porth yr Ogof since 1957,^[2][3] and all but one have lost their lives in the cold, fast-flowing and 4-5 metre deep Resurgence Pool at the far end of the cave, where the river Mellte resurges (emerges).

No one should attempt to cross this pool or leave the cave by this route unless they are properly equipped, are excellent swimmers, and have the training and experience to do so safely.^[4]

Geological and human history

'Porth yr Ogof' means 'the mouth of the cave' in Welsh, most notably because of the gaping maw that is the Main Entrance. The cave lies on the Afon Mellte and is located in a comparatively narrow band of carboniferous limestone. The river bed is dry from Ystradfellte onwards, the river only rising to the surface again just before the cave.

The cave has been known to humans for many centuries , as it is not easily overlooked once one is in the valley, but because of the passageway's susceptibility to severe flooding there has been no evidence found of any prehistoric human habitation. The cave and its many visible fossils was mentioned in the writings of Edward Lhuyd, and in the 19th century it was mentioned again by the first pioneers of caving.

References