Another wild camp

Garreg Las is a minor summit on Y Mynydd Du, with extensive areas of glaciated pavement and periglacial landforms, a geology map shows an interesting outcrop pattern of geology and faulting, The OS map shows some topographic relief, open access upland and the time of year with the azimuth of sunrise to the north of the Carmarthen Fans. All in all sufficient inspiration for a wild camp trip to explore the dusk/dawn potential with a reasonable forecast and good visibility.

A window into the Y Mynnyd Du geology and faulting @ British Geological Survey

Parking up and it was good to see an absence of litter and information boards installed, even the limekilns and quarries were receiving some TLC, part of the Calch project on the areas long history of Lime production. The walk in was warm and I ended up pitching the tent near a small 'peat' pool on the NE flank of Foel Fraith, the level mossy turf almost negated the benefit of an inflatable mat. With the tent pitched, myself foddered and watered, I made my way over to Garreg Las, to record the geology and see what unfolded for sunset.

Foundered glaciated pavement

The sandstone outcropping on Garreg Las, is classed as a quartz arenite, a hard, durable sandstone and its competence is indicated by the outcrop exposure. Large areas show evidence of being scoured and quarried by glacial ice and there is evidence for periglacial processes breaking up the pavement and movement of loose material downslope into lobes and sheets. In places the quartz sandstone has foundered, presumably where the underlying limestone has dissolved away. Erratics resting on the foundered rock point to collapse after deglaciation.

Weathered surface

The sandstone pavement on the western side, appears extensively weathered, there is an absence of fresh striae and chatter marks and intriguingly there are some sizeable weathering pits/pot holes, landforms I have also seen on bedrock in the hills of the Cairngorms and Norway. It is thought that the formation of weathering pits is an erosion phenomena associated with high wind and the scouring or abrasive action by loose rock/grains and water. Field studies in the Cairngorms revealed limited formation of weathering pits/pot holes in recently glaciated areas and deeper weathering pits were confined to relict surfaces. Cosmogenic radiation dating of the Cairngorm bedrock surfaces with weathering pits revealed an exposure age range of ~ 21,000 - 79,000 years for glaciated areas and ~50,000 - 250,000 years exposure age for unglaciated areas. The vertical joint/fracture surfaces also displayed 'cavernous' weathering on the west side of Garreg Las, whereas I didn't notice any weathering on vertical surfaces on the eastern side, features that suggest two episodes of pavement break up. To my eyes, the weathered appearance and presence of weathering pits does suggest that some surfaces on Garreg Las have been exposed for a long period of time, on the other hand, it may just be a less competent area of sandstone.

Weathering pit 

The summit of Garreg Las, Twyn swnd, is adorned with a pair of large bronze age cairns, Carnau'r garreg las, and visible on the skyline from a number of directions, mostly from higher ground/upland areas.

Carnau'r garreg las

I'd hoped for a view to the north for sunset, but haze reduced visibility and on the NW horizon a solid band of cloud was evident with streamers of cirrus clouds. I was also beginning to question my wisdom at leaving a tele zoom out of the bag. Considering the options I headed back downslope to an area on Cefn y Garreg Las where there were some larger erratics and an area of flowering bog cotton.

Weak sunlight and Incoming cloud at sunset

Returning to the tent, I reflected on my inability to find a composition on Garreg Las that convincingly illustrated a down faulted block of younger geology against older geology. I made a note that the geological faulting of Garreg Las, would probably be better photographed later in the year towards the winter solstice using the low angle of light to model the geology and from a viewpoint elsewhere on Y Mynydd Du. Still, there was the promise of dawn and a view of the Welsh Borderland Fault System to north.

Sunrise

A look out the tent in the gloaming of dawn revealed the depressing sight of clear skies overhead and to the south, with a band of cloud to the north and north east. The 3rd successive photography trip at dawn with clear blue sky overhead and the sun rising into cloud, deep sigh. So, twilight photography bite the dust for a start, sunrise seemed destined to follow suit and when the sun eventually cleared the cloud, any shadows would be an unappetising blue shade, the colour cast courtesy of the overhead clear sky, not the best as grey rock would really accentuate the 'blue' shade. I had a dark suspicion that the band of cloud responsible for masking sunset, was the very same cloud mass which would now obscure sunrise. Still there was some mist around in the valleys and pretty good visibility, which gave some hope.

100mm field of view of Welsh Borderland Fault System

Reaching the northern slope of Garreg Las and a look out to the NE horizon gave confirmation that there would be no warm side lighting at sunrise.  Things looked more positive to the North with colour in the clouds and valley mist highlighting the Welsh Borderland fault system. I now wished I'd packed a telephoto zoom, as 100mm was too wide on the vertical angle of view and needed a vertical crop to get the view sans foreground. The Welsh Borderland fault system delineates a terrane boundary separating the Cymru and Wrekin terranes, stretching from Pembrokeshire to Shropshire.

Desired crop

On up into the boulder field and with neutral coloured rock, I really would have liked the warm light of sunrise and cloud overhead. Instead it was matter of trying to find a view that showed the extent of the periglacial breakup and mass movement of debris downslope and keep enough warm light rock to offset the blue shade.

A powder blue sky and harsh summer light, meant my inspiration dried up shortly afterwards and it was a case of recording some geology outcrops on the way back to the tent and the journey back home reflecting on events.