Glyn Tarell geotrail
A dramatic journey into Fforest Fawr Geopark.
This tough but illuminating route, which takes you to the plateau of Fforest Fawr, involves some walking off marked footpaths. At the end, you’ll know how ice shaped these landscapes and why the Brecon Beacons National Park is home to Wales’s first European Geopark.
Need to know
Length: 6¼ miles (10km)
Time: Around 3–4 hours
Start and finish: Storey Arms, on A470 between Brecon and Merthyr Tydfil
OS map ref: SO 982203
OS map: OL12 Explorer (1: 25 000 series)
Facilities: Car park at Storey Arms. Toilets are located at the next car park, a few hundred metres to the south.
Along the way
It’s a good starting point, not just for the walk but as an introduction to how glaciation during the last Ice Age – which ended around 10,000 to 12,000 years ago – shaped the Brecon Beacons we see before us today. You’re at the centre of the last great ice sheet that covered the region. The ice initially melted away around 15,000 years ago, though the high cwms were reoccupied by glaciers for a short-lived cold period around 10,600 years ago. Storey Arms stands in a critical spot at the saddle (or col) between the Tarell valley to the north and Taf valley to the south. Both valleys are glacial troughs with a classic and characteristic U-shape, scoured out by ice around 25,000 years ago, the col representing a former ‘ice-divide’ at the centre of the last glacier.
On the northern side of 734m-high Fan Fawr, in a shallow hollow at around 560m, you’ll see a collection of hummocks and ridges. These may reflect the existence of a small glacier or rockfalls that occurred over snow or ice on the flanks of Fan Fawr around 10,600 years ago. Look at the boulders or stones making up these ridges – you may find striations, scratch marks created by the scouring of ice.
This walk takes you into the area known as Fforest Fawr (The Great Forest), so called not because of its tree cover but to signify its ancient status as a hunting ground. Its high, wild moorland gives its name to Fforest Fawr Geopark, created in 2005..
Here’s one of the National Park’s most compelling, fascinating features. Although just a stone’s throw from the busy A470, this atmospheric amphitheatre of soaring, craggy cliffs seems a world apart, solitary and self-contained. It’s a National Nature Reserve (NNR) thanks to its fascinating range of arctic alpine plants. Craig Cerrig-Gleisiad’s dramatic, steep-sided crags and lumpy, bumpy lower slopes were created during the Ice Age when snow that collected in the north-facing slopes eventually turned into a glacier. The scooping and grinding action of the ice carved the 150m-high cliffs, and when the glacier eventually retreated it deposited the debris within it to create what are known as moraines – the mounds and hillocks that are clearly visible in the bowl beneath Craig Cerrig-Gleisiad’s dark crags. Given its genesis and shady, brooding character it’s somehow appropriate that the NNR is famous for its rare arctic-alpine plants such as purple saxifrage and serrated wintergreen. They survive here at or near their southern limit in Britain (and do not reappear again until the Alps), clinging to Craig Cerrig-Gleisiad’s ledges, gullies and crags. Their inaccessibility has also contributed to their survival, so you are asked not to climb the steep crags or screes for a closer view – please bring binoculars.