Mapping Mountains – Trimble Surveys – Glyder Fawr

 

11.08.24  Craig Cwrwgl (SH 615 615) 

One of the most obscure and esoteric of Welsh summits is a great pillar of rock that forms part of the evocatively named Craig Cwrwgl, ‘coracle crag’.  These rocks front the north-eastern face of Elidir Fawr, and eventually give way to steep slopes that plunge into the dark waters of Marchlyn Mawr.

Craig Cwrwgl (SH 615 615).  Photo: Aled Williams

The detachment of the pillar from the bulk of Elidir Fawr is unusually complex.  In addition to the original bwlch (col, pass) that consists of bedrock and defines the traditional separation of a top from its parent mountain, the gap above the bwlch is also spanned by two rock-bridges, one being lower than the other.  These rock-bridges are the suspended remnants of towers that fell from the pillar and were held from falling further by the adjacent hillside.  Remarkably, the higher of the two towers fragmented upon impact into three large boulders and the cracks between each of them are permeated by small holes.

The upper rock bridge above the natural bwlch.  Photo: Aled Williams

Typically, a bwlch between mountains, hills or tops represents both the apex in the valley-to-valley traverse as well as the trough in the hill-to-hill traverse.  In this case and at the present time, it may be argued that the original bwlch only represents the valley-to-valley apex, while the higher of the two rock-bridges represents the hill-to-hill trough.  Conversely, it is fact that the rock-bridge does not, and never did, represent the valley-to-valley apex, whereas the original bwlch has unequivocally represented both at one time in natural history.  Does this matter?  Well, it does if the prominence of the pillar is to be measured, and it was for this purpose that I intended to climb Craig Cwrwgl.

Gearing up for the climb.  Photo: Aled Williams

The first-recorded ascent of Craig Cwrwgl was by J. M. Archer Thomson and W. J. Williams in April 1900, and because a name had not been recorded by the Ordnance Survey, Thomson initially referred to it as the ‘Pillar of Elidr’.  However, by the time Thomson published his guide-book ‘Climbing in the Ogwen District’ in 1910, he had discovered its actual name through local enquiry to be Craig Cwrwgl.  124 years later, the plan for the day was to climb up the pillar in one-pitch via its easiest route that first ascends to the bwlch along the westward-draining gully and then across the upper rock-bridge to the feature referred to by Thomson as the ‘Rift’, which is one of the several deep fissures that divide the upper half of the pillar into separate towers.  The climb would be led by the safe-hands of experienced local climber Gwyn Jones, as kindly arranged by Eric Jones, who accompanied us to the foot of the pillar.

Climbing to the bwlch.  Photo: Aled Williams

Gwyn led confidently up the gully and made it look easy until a slippery slab slowed his progress three-quarters of the way up.  After a bit of gardening he soon overcame the slab and quickly disappeared into the alcove underneath the upper rock-bridge.  He re-emerged and swiftly shifted up and across the wedged boulders, and within another 5 minutes he was standing on top of the pillar.  The gauntlet had been laid!  After some sound advice from Eric I followed Gwyn’s route up the gully.  All went relatively well until I arrived at the slippery slab, which was smooth, muddy and slimy, dotted with woodrush plants that would slide off the rock upon any attempt to use them as climbing aids!  After a good few minutes of undignified dithering I stretched up and found the key hold, and with a sturdy pull upwards I was soon above the slab and into the relative safety of the bwlch.  The next set of moves involved gaining the upper rock-bridge, which was done by climbing a short chimney on the Elidir Fawr side of the bwlch.  An easy walk over the suspended boulders brought me to the bottom of Thomson’s ‘Rift’.

Thomson's 'Rift' and the view from the upper rock bridge.  Photo: Aled Williams

As I squeezed into the fissure, Gwyn’s voice echoed down from above advising me to freestyle with the use of any body parts to inch my way up it.  Despite a couple of awkward places, the chimney proved enjoyable; no doubt helped by the reduced exposure felt within its claustrophobic structure.  As described by Thomson in 1910, emergence from the fissure onto the summit rocks of the pillar did indeed prove to be ‘somewhat of a coup de théâtre’!

The summit of Craig Cwrwgl.  Photo: Aled Williams

We were not alone on the summit, as two other climbers were in the process of finishing their climb on the east side of the pillar.  The views were stunning and unusual, with a distant Mynydd Hiraethog framed in by the rugged precipices of Pen yr Ole Wen and Foel Goch.  Perched on a luxurious mat of grass and crowberry, it was easy to forget the encircling precipices when looking out at such a vista.  I peered over the edge and waved down to Eric to inform him that we had made it.

Eric from the summit.  Photo: Aled Williams

It was now time to survey the summit.  The high point was easy to locate and having asked Gwyn and the other two climbers as to their opinion, we all agreed on the point to be surveyed.  As the other climbers prepared to abseil down, I hopped over a deep and wide crack between the summit towers and set the Trimble up for measurement.  Once sufficient data was collected, we waited for the climbers to complete their abseil before Gwyn prepared the gear for our likewise descent to the bwlch.

Surveying the summit with the Trimble GeoXH 6000.  Photo: Aled Williams

A short abseil brought me back down to the upper rock-bridge.  I set the Trimble up on the boulder closest to Elidir Fawr, immediately above the low-point of the upper rock-bridge, taking a 106cm offset with a tape measure.

Returning to the bwlch.  Photo: Aled Williams

By the time a full dataset had been collected by the Trimble, Gwyn was also down and was free to help me with the surveying.  I descended to the alcove underneath the rock-bridge to take the measurement offset from the Trimble position to the low point of the original bwlch, which came to 405cm.  Gwyn then set up another abseil point and brought us down safely and quickly to the base of the pillar.  By early evening we were back at the vehicles after a great day out on the hill.  With great gratitude I thanked Gwyn and Eric for getting me up Craig Cwrwgl and for their unwavering patience with the time-consuming surveying.

How the bwlch was surveyed: the red ‘X’ marks the spot where elevation was measured with the Trimble GeoXH 6000, the yellow line roughly represents the 106cm offset from the Trimble GeoXH 6000 to the hill-to-hill bwlch (i.e. the rock-bridge) and the white line roughly represents the 405cm offset from the Trimble GeoXH 6000 to the valley-to-valley bwlch (i.e. the original bwlch)

 

Aled Williams (August 2024) 

 

Survey Result:

 

Craig Cwrwgl

Summit Height:  761.2m (converted to OSGM15)

Summit Grid Reference:  SH 61544 61586

Bwlch Height:  746.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 61546 61584

Drop:  14.5m

Dominance:  1.90%

 

Note: if taking the rock-bridge as the bwlch, the drop comes to 11.5m

 

 

For further details please consult the Trimble Survey Spreadsheet