Mapping Mountains – Trimble Surveys – Glyder Fawr

17.08.24  Elidir Fach (SH 603 613) 

A chilly early morning walk through the upper portion of Chwarel Dinorwig brought me onto the open hillside beneath the summit of Elidir Fach.  Shortly after the release of new Welsh LIDAR data in early 2023, this hill was deleted from the Subs of The Welsh Highlands list due to the resultant 9.8m drop failing the 10.0m qualification threshold.  Ever since, this hill has been high on the priority list for an accurate Trimble GeoXH 6000 survey.

The first survey for summit position and height.  Photo: Aled Williams.

The summit of Elidir Fach consists of a shelter-cairn built around small outcrops of rock, one of which being a contender for the high point of the hill.  Beside the cairn on the north side is another contender, a small outcropping rock, seemingly at the central point of the summit dome.  A third contender is a larger boulder found to the south of the cairn among a collection of weathered outcrops.  I checked each out from various angles with an Abney level, but struggled to definitively rule out one of the others.  There was only one thing for it – three summit surveys were necessary!

The second survey for summit position and height.  Photo: Aled Williams.

I thankfully had the summit all to myself for the duration of the surveying, free of distraction and interruption.  This proved unusual as over the next hour no fewer than eight people would come and go from this minor top.

The summit area with the Trimble at the third summit contender.  Photo: Aled Williams.

The next phase was to survey the bwlch, which I knew in advance would entail two sets of measurements given that LIDAR data gave two positions of equal height.  I was however glad of LIDAR positioning, as the flat expanse of the bwlch made judging the low point by eye extremely difficult.

The bwlch backed by the upper slope of Elidir Fawr.  Photo: Aled Williams.

As data collected on the bwlch, I looked upon the continuation of the Eryri peaks either side of it with the pastoral lands of Môn stretching on beyond the Menai.  I felt glad to be born a Welshman!  I packed up the equipment and headed back down to the car.  It had been an enjoyable morning on the hill and I was looking forward to know the outcome of the surveying work.

Surveying one of the two options for the critical bwlch.  Photo: Aled Williams.

Surveying one of the two options for the critical bwlch.  Photo: Aled Williams.

 

Aled Williams (August 2024)

 

Survey Result: 

 

Elidir Fach

Summit Height:  794.2m (converted to OSGM15)

Summit Grid Reference:  SH 60377 61341

Bwlch Height:  784.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 60556 61279

Drop:  10.0m (Welsh Highland Sub reinstatement)

Dominance:  1.26%

 

 

For further details please consult the Trimble Survey Spreadsheet

 

 

 

  

Mapping Mountains – Trimble Surveys – Glyder Fawr

14.08.24  Pt. 914.9m (SH 659 585) 

My expectations were high as I admired the rocky bulk of Glyder Fawr from the warm cradle of Cwm Bochlwyd.  I had previously been thwarted in an attempt to survey the largest of the pinnacles situated on the north-east ridge of Glyder Fach.  On that occasion, I had come ill-equipped for winter conditions, which precluded a direct ascent of the ridge from Bwlch Tryfan.  Revising the plan, I had then tried to descend to the pinnacle from the summit plateau of the mountain, but owing to the ground conditions, was forced to dampen my ambitions and be content with surveying just the higher of two significant pinnacles found on the ridge.

Glyder Fach from the shore of Llyn Bochlwyd.  Photo: Aled Williams

Arriving at the base of the ridge provided welcome respite from the sun.  After a short break, I started climbing the gully that provides the easiest route to the upper ridge.  The coned-profile of Tryfan basking in evening light dominated the view out from its confines.  The scrambling was entertaining and brought back good memories of various ascents made during the last 20 years.

The view down the gully.  Photo: Aled Williams

The distant sound of walkers heading back to civilisation confirmed my hopes that I would have the ridge to myself.  This would greatly help the task of surveying, which was now imminent.  The view of the pinnacled upper ridge was as impressive as I recalled and I began to wonder what surveying challenges would be presented.

The continuation of the ridge toward Glyder Fach.  Photo: Aled Williams

Thankfully, the summit of the pinnacle was relatively easy to survey.  I used my rucksack to create a platform whereby the receiver of the Trimble GeoXH 6000 was mounted on the highest point of rock.  As I secured it in place, I noted the drop on the eastern side and a sense of dread hit me as I thought of Myrddyn’s expensive surveying equipment plunging down into the upper recess of Cwm Tryfan!

The Trimble GeoXH 6000 gathering data at the summit of Pt. 914.9m (SH 659 585).  Photo: Aled Williams

The Trimble GeoXH 6000 gathering data at the bwlch of Pt. 914.9m (SH 659 585).  Photo: Aled Williams

A short bit of down-climbing brought me to the bwlch.  The low point was found to be a notch close to the base of the pinnacle.  As I anticipated that the Trimble would struggle to reach its accuracy level in such a tight spot, I decided to elevate the equipment on my rucksack and took an offset using a tape measure.  No problems occurred during measurement and after 8 minutes of data gathering I closed the Trimble off.

A fine addition to the ranks of Welsh Highland Subs.  Photo: Aled Williams

The Trimble GeoXH 6000 set-up position at the bwlch.  Photo: Aled Williams

I then sauntered up the remainder of the ridge, passing over the lower prominence, albeit higher in elevation, pinnacle that I had surveyed the previous year.  As I arrived on the summit plateau of Glyder Fach, signs were apparent that the weather was changing.  A bank of cloud was rapidly filling in Nant Gwynant and a chilling breeze was picking up in strength from the south-west.  My visit was well timed.  By the time I returned home, rain and high winds had set in.

Wisps of evening mist gathering around Castell y Gwynt

Aled Williams (August 2024) 

 

Survey Result: 

 

Pt. 914.9m

Summit Height:  914.9m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SH 65981 58563

Bwlch Height:  904.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 65982 58556

Drop:  10.5m (Welsh Highland Sub addition)

Dominance:  1.15%

 

 

For further details please consult the Trimble Survey Spreadsheet

 

 

 

  

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

 

Mapping Mountains – Trimble Surveys – Glyder Fawr

04.03.23  Pt. 924.4m (SH 659 585), Castell y Gwynt (SH 653 581), Pt. 929.0m (SH 656 579) and Pt. 872.3m (SH 658 577) 

Today I wanted to survey a number or rocky peaks on Glyder Fach.  Early travel writers would often overuse the word stupendous to describe the natural features of Eryri, but this mountain truly deserves the adjective.  I set off from Pen y Gwryd under leaden skies.  The conditions were mild and the mist was confined to elevations above 900m.  Upon reaching the plateau above Llyn Caseg Fraith, I noticed that my surveying plans may be compromised by the presence of snow that was earlier blanketed by the clouds.  This was unexpected and I was not equipped with winter mountaineering gear. 

The mist enshrouded ridge (Photo: Aled Williams)

My original plan was to first descend to Bwlch Tryfan to then ascend the north ridge of the mountain, thus allowing the surveying of some of its impressive pinnacles.  However, the snow conditions looked threatening.  Knowing that the most difficult scrambling was found on the lower half of the ridge, I decided that I would first ascend to the top of Glyder Fach and then investigate whether a descent to the pinnacles on the ridge was possible.  As the upper slopes of Glyder Fach were gained, the prospect became increasingly ominous!

An expanse of mist and snow (Photo: Aled Williams) 

By the time I had reached the high plateau of the mountain, I was in cloud.  It was a monochrome scene, the whiteness of the snow and sky interrupted by the dark outlines of naked rock.  The absence of wind provided a quiet stillness; another world to that found below the cloud.  The top of the north ridge came into view, which signalled decision time.  Would I venture down along its serrated snow-clad edge?

Top of the ridge (Photo: Aled Williams)

My feet awkwardly crested the first few boulders.  I slipped slightly and sensed the plunge that waited down to the recesses of Cwm Bochlwyd.  Compensating my weight to the right, another wave of exposure greeted me as I spied the rime-encrusted rocks disappearing into the void of Cwm Tryfan.  Luckily, there was no ice and this provided me the confidence to move forward slowly and carefully.

Looking down the upper section of the ridge (Photo: Aled Williams)

I eventually arrived at my first survey point of the day.  This was a narrow gap in the ridge at the top of a steep gully, which provided the land bridge between the highest pinnacle and the bulk of the mountain.  The pinnacle itself looked inaccessible and I doubted whether I would be able to climb it in the conditions for the purpose of measuring its height.  The primary target of the day was immediately behind the highest pinnacle, a peak that stood a chance of making P10 status and therefore inclusion into the Subs of The Welsh Highlands list.  Unfortunately, it soon became apparent that I would not be able to survey it, since the routes to it were too dangerous in the conditions.

The upper pinnacle (Photo: Aled Williams)

Having accepted that the lower pinnacles were out of reach, I focused on surveying the highest pinnacle.  The critical bwlch was quickly located and the Trimble was placed in position.  It took around ten minutes for the equipment to attain its optimal accuracy levels, hampered by the enclosed nature of the location.  This wait provided time for devising a strategy that would allow the top of the pinnacle to be measured for absolute height.  The strategy was duly executed and it quickly became apparent that I would not be able to place the Trimble at the highest point of rock.  However, by jamming my body in a cleft between two rocks and awkwardly contorting upwards, I was able to attain a position where the equipment could be held in place just below the summit.  A long two minute wait ensued as data was collected, at the end of which I had lost all sensation in my fingers!  The offset between he Trimble antenna and the highest point was taken before I gingerly descended to the relative safety of the bwlch.

Back on relative terra-firmer (Photo: Aled Williams)

I then re-traced my route upwards along the ridge.  I was glad to reach the high plateau again, happy that the morning’s adventure was at an end.  The next objective was Castell y Gwynt, although a quick visit to the summit of Glyder Fach provided a prelude.  

The summit area of Glyder Fach (Photo: Aled Williams)

Castell y Gwynt (SH 653 581) (Photo: Aled Williams)

The climb up Castell y Gwynt was completed with relatively little difficulty and the Trimble was soon gathering data on the highest rock.  I felt perched as I looked down on the plateau below.  Once descended the critical bwlch was located and the equipment was soon beeping away again as yet another data set was collected.  As I sat waiting, I admired the rock architecture of this fine top with its cathedral-like spires seemingly piercing the sky above.  However, my ruminations were suddenly interrupted by two ice-axe-equipped individuals creeping up towards the Trimble as they contemplated a route up the peak.  I greeted them with: “If you could steer clear of the yellow thing that would be appreciated”, to which one replied: “what is it?”, and without explanation I shouted “a GPS”!  Nothing more was said apart from a “thank you” as they retreated on to other things.

The bwlch of Castell y Gwynt (Photo: Aled Williams)

The penultimate tor to gather data from (Photo: Aled Williams)

There were two other tors that I wanted to survey on the way back to Pen y Gwryd.  These have always caught my attention when travelling along the road from the south and their surveys were long overdue.  The first proved to be another dramatic top, with a pleasing view down to Cwm Ffynnon.

One of the two rock tors surveyed on the descent (Photo: Aled Williams)

The last surveying objective of the day (Photo: Aled Williams)

The second top stood at the limit of the snowline.  Its form consisted of a terrace made up of huge pillars, permeated by deep cracks and chimneys.  Two summits were investigated with data gathered on each, despite the eye having judged the western point to be comfortably higher.  All that remained was a steady plod back to the car to bring another good day on the hill to a close. 

Aled Williams (March 2023) 

 

Survey Result:

 

Pt. 924.4m

Summit Height:  924.4m (converted to OSGM15)

Summit Grid Reference:  SH 65975 58541

Bwlch Height:  917.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 65971 58536

Drop:  6.6m

Dominance:  0.72%

Castell y Gwynt

Summit Height:  975.7m (converted to OSGM15) (average of two Trimble GeoXH 6000 surveys) (significant height revision)

Summit Grid Reference:  SH 65397 58181

Bwlch Height:  959.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 65419 58194

Drop:  16.0m

Dominance:  1.64%

Pt. 929.0m

Summit Height:  929.0m (converted to OSGM15)

Summit Grid Reference:  SH 65625 57979

Bwlch Height:  921.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 65639 57995

Drop:  7.9m

Dominance:  0.85%

Pt. 872.3m

Summit Height:  872.3m (converted to OSGM15)

Summit Grid Reference:  SH 65867 57758

Bwlch Height:  867.0m (converted to OSGM15)

Bwlch Grid Reference:  SH 65876 57793

Drop:  5.3m (Welsh Highland Sub deletion)

Dominance:  0.61%

For details on the 1st survey of Castell y Gwynt

For further details please consult the Trimble Survey Spreadsheet