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
Porth yr Ogof car park, at the time of writing,
is manned most days by an employee of the Brecon Beacons National Park.
There is a car park charge of £4 per day
for Motor Cars £7 for minibus..
Access to the cave entrance
is located just a few minutes walk from the car park. The ascent to
the cave from the car park is very steep. As the
footpath is formed
from the exposed limestone rock it is deeply grooved and uneven. Children
should be supervised and adults should also take particular care. This
foot path may not be suitable for everyone including young children, the
elderly, disabled or infirm.
National Park signs warn of the dangers of:
Porth yr Ogof:
Porth yr Ogof translates as the gateway to the cave.
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.
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:
Currently nearly 3 km of the cave system at Porth
has been explored. This cave system is very popular
with cavers and with groups from outdoor centres. It should be noted
that deaths have occurred and that passage through the cave system
should only be attempted by experienced cavers, who are well equipped,
and have local knowledge, or are being led by an
experienced caving instructor with local knowledge of this particular cave
system. It is essential that you verify the accreditation and local experience
of any instructor. Caving Guide to the Brecon Beacons
Only experienced cavers and with local
knowledge should attempt to explore the cave system at Porth yr Ogof.
- This cave system has claimed more lives than any other cave in
In periods of rainfall the cave entrance and the
passageways can fill with water very quickly.