upland walks and deeply incised river gorges and waterfalls to rival any in the UK. The Brecon Beacons are the highest summits in the park, with Pen y Fan not quite making ‘Munro’ status, being just short of 3000ft. Although this area lacks the challenges of the narrow rocky ridges of the Lake District and Snowdonia, it does provide opportunities for a real mountain expedition in exciting winter conditions. Finally, the Black Mountains, on the English border, have a softer feel to them, without the coarse and rugged Welshness of Mynydd Du.
There is also a plethora of things to see and activities for visitors of all ages and tastes, making the park a great place for families to visit. Favourite attractions for children include Dan-yr-Ogof Show Caves in the Swansea Valley, Brecon Mountain Railway at Penderyn and Big Pit National Coal Museum near Blaenavon. Picturesque market towns on the edges of the park, such as Llandovery, Brecon, Crickhowell and Abergavenny, are also great places to explore.
Geology of the Brecon Beacons
The rocks that shape the park belong to the Old Red Sandstone and were deposited some 395–345 million years ago in the Devonian period of geological time. Old Red Sandstone is a generic term which refers to a group of sedimentary rocks laid down by rivers flowing across coastal plains. Three distinct rock types, conglomerates, sands and muds, were formed from river gravels, sands and muds respectively.
South Wales lay south of the equator in latitudes which are typically occupied by deserts. Prior to this, much of Britain was affected by strong earth movements which caused uplift and sharp folding, resulting in a tract of upland (St George’s Land) which probably extended from the Midlands through central and northern Wales and into Ireland.
Flash floods washed down red muds, sands and grits along ephemeral river channels, building an extensive river flood plain. To the south was the Devonian shoreline, approximately where the Bristol Channel is now, and the warm Devonian Sea where the first fish swam. Europe at this time was drifting northward and, when it crossed the equator, the semi-arid flood plains were gradually submerged beneath tropical Carboniferous seas.
The Old Red Sandstone in the Brecon Beacons can be split on geological grounds into Lower and Upper, the Middle being missing. The Lower Old Red Sandstone comprises a group of up to 850m of red marls followed by a group of sandstones divided into two formations – the Senni Beds, some 310m of dark green chloritic layers interbedded with red, and the Brownstones, 330m of very dark red and purple sandstones. The steep craggy slopes are formed from these regularly bedded Brownstones.
A secondary escarpment is well developed on the northern ridges of Cefn Cwm Llwch, Bryn Teg and Cefn Cyff where the ridge drops steeply from the main scarp, flattens between 540 and 600m and then drops again, the steeper slopes beneath this being cut in the Senni Beds which underlie the Brownstones.
The Upper Old Red Sandstone comprises three groups of rocks. The Plateau Beds are red quartzites and conglomerates up to 33m thick which unconformably overlie the Brownstones. The summits of Corn Du and Pen y Fan are capped by an isolated outlier of some 14m of overlying, massively bedded, Plateau Beds. The second group, the Grey Grits, are unfossiliferous sandstones and conglomerates up to 200ft thick and these pass laterally eastwards into the Quartz Conglomerates which comprise red and brown sandstones, quartzites and coarse conglomerates. Further earth movements during the mid-Devonian period uplifted South Wales, resulting in renewed erosion, creating a distinct break in the geological record, and forming the distinctive ridges and valleys that walkers enjoy today.
Pen y Fan from the Cribyn face path
Earth movements
Mountain building earth movements which took place at the base of the Old Red Sandstone and at the end of the Upper Palaeozoic have been named the Caledonian and Hercynian, respectively. Caledonian movements spanned a time interval of more than 100 million years, at least from latest Cambrian to post-Silurian, and were responsible for folding and faulting of rocks, resulting in geological structures aligned in a north-east–south-west direction. After these mid-Devonian movements died away, there was little mountain building until late Carboniferous times. At the end of the Coal Measures, the Brecon Beacons were on the southern flanks of a southward-moving continent which eventually collided with a northward-moving land mass to the south. Enormous compressive forces caused strong folding and faulting of Upper Palaeozoic rocks. The outstanding feature that resulted from these tectonic movements is the syncline of the South Wales coalfield and the regional southward tilt of the rocks of the Brecon Beacons originated as part of its northern limb. A major structure disrupts the northern rim of the coalfield and runs through the lower parts of the Waterfall Country. This is a complex fault system known as the Neath Disturbance which grew intermittently from Dinantian times, reaching its zenith in late-Carboniferous times.
Glacial origins of U-shaped valleys
The valleys were originally formed by streams cutting down through the Old Red Sandstone rocks, forming a V-shaped cross-section. For some two million years this area was in the grip of the Ice Age which ended about 10,000 years ago. Glacier ice carved out U-shaped valleys and towards the end of the Pleistocene, when climatic conditions were still sufficiently cold for significant quantities of snow to collect, many cwms were formed.
Changing Woodland
Trees started to recolonise the Brecon Beacons after the last Ice Age around 12,000 years ago. Arctic-alpine vegetation first established itself, and was then invaded by a scrubland of dwarf birch with some juniper. Taller birches and, to a lesser extent, Scots pine, followed.
Woodland flowers in Cwm Cumbeth
The climate continued becoming warmer and drier and, around 9000 years ago, pine and birch remained on lower hill slopes but the upland was covered in hazel, with valleys full of damp oak woodland with lime and elm. Woodland grew at much higher altitudes than it does today, up to 600m, above which grew alpine grassland.
Climatic conditions then became even warmer and more humid allowing the formation of blanket peats 7000–5000 years ago. Alder, elm and oak thrived in damp valleys. Drier conditions returned, elm disappeared and beech made its first appearance. The climate started to decline again and has continued to do so to the present day. Sessile oak, ash and beech woodland developed in this period and still dominate the landscape today.
Human Impact
The Brecon Beacons may appear to be a bleak and inhospitable place to live but prehistoric man is known to have settled here since Mesolithic times (Middle Stone Age c6000BC). The climate in Mesolithic, Neolithic (New Stone Age c3000–1800BC) and Bronze Age times (c1800–400BC) was much warmer and drier than today’s and the mountains were covered in oak, birch, alder and lime woodland, with an understorey of hazel and willow.
Woodland glades would have contained grasses, heathers, species of rose and various flowers. Prehistoric man fed, clothed and housed himself by hunting and gathering, and, by about 2500BC, woodland clearance and mixed farming was practised. During the very dry summer of 1976 when the water level was extremely low, many scrapers, arrowheads and knife blades were found in the Upper Neuadd reservoir.
An improvement in Britain’s climate from about 4500 years ago heralded the start of the Bronze Age and was associated with the spread of agriculture
