Mapping Mountains – Significant Height Revisions – Welsh Highlands – Uchafion Cymru

 

Castell y Gwynt (SH 653 581) 

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from two Trimble GeoXH 6000 surveys conducted by Myrddyn Phillips on the 16.05.14 and Aled Williams on the 04.03.23. 

Castell y Gwynt (SH 653 581)

The criteria for the list that this height revision applies to are:

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Castell y Gwynt and it is adjoined to the Glyder Fawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A5 road to its north and the A4086 road to its south, and has the village of Capel Curig towards the east.

When the list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 16m of drop, based on a series of basic levelling surveys conducted by Myrddyn Phillips and listed with a 972m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and a 956m bwlch height, based on the height difference between the summit spot height and the drop value ascertained from the basic levelling survey. 

Extract from the Ordnance Survey 1:25,000 Explorer map

The summit of this hill has now been surveyed twice with the Trimble GeoXH 6000 and it is the average of these results that is being taken, resulting in a 975.7m summit height positioned at SH 65397 58181, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

The Trimble GeoXH 6000 gathering data at the summit of Castell y Gwynt on the 16.05.14

Therefore, the new listed summit height of this hill is 975.7m and this was derived from the average of two Trimble GeoXH 6000 surveys, this is positioned at SH 65397 58181 and is 3.7m higher than its previously listed height of 972m which was based on the summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Glyder Fawr

Name:  Castell y Gwynt

OS 1:50,000 map:  115

Summit Height (New Height):  975.7m (converted to OSGM15)

Summit Grid Reference:  SH 65397 58181  

Bwlch Height:  959.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 65419 58194

Drop:  16.0m

 

Myrddyn Phillips and Aled Williams (May 2023)

 

 

 

 

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

 

  

Mapping Mountains – Trimble Surveys – Glyder Fawr

16.05.14  Glyder Fach  (SH 656 582) and Castell y Gwynt (SH 653 581)

Glyder Fach (SH 656 582)

With the weather set fine Ed wanted to indulge in a warm weather scramble, and we decided upon Y Gribin, a rocky ridge that crests the Glyderau plateaux between Glyder Fawr and Glyder Fach.  I’d been on this ridge a few times with Ed, and it never disappoints, easier routes can be found on its west side but the crest of the ridge is enjoyable, with enough exposure for caution and excitement.

We parked beside Ogwen Cottage (SH 649 603), the small café and toilet block has changed since my last visit as it has been re-built, it now looks very swish with outdoor seating, disabled parking bays and nicely arranged wooden boards with contouring displaying each hill and its height.   

The cafe and toilet block at Ogwen has now been re-built

Would the 994m height be retained after being Trimbled?

We left the car at 9.50am and estimated the walk would take us 6 – 6½ hours, the main path from Ogwen heads toward Llyn Idwal with a narrower path leaving it shortly after the bridge that spans the Afon Idwal, it is this narrower path that we followed as it headed up toward Llyn Bochlwyd (SH 654 592).  From the lake the main path heads south-east towards Bwlch Tryfan, the last time I’d been this way was with Ted Richards when he celebrated his completion of the Welsh Nuttalls on Tryfan.  We now branched west on a narrow path that aims for the lower grassed section of Y Gribin.

Y Garn (SH 630 595) seen from the approach to Llyn Bochlwyd

The view from Llyn Bochlwyd with the top of Y Gribin in centre of photo

As the lower section of Y Gribin is reached the direction of the path swings southward and heads up gaining ground as the panorama of peaks opens up, to the west is Y Garn rising above the waters of Llyn Idwal while to the east is Tryfan, majestic in its dominance above Llyn Bochlwyd.

Y Garn rising above the waters of Llyn Idwal

Tryfan majestic in its dominance above Llyn Bochlwyd

About half way up the ridge the ground opens up on to a relatively flat grassed area, similar to a football field, above is the ridge proper, looking rather daunting in its upper section as it thrusts up to the Glyderau.  The path keeps to the right of the ridge crest, by far the safer option.  However, I’ve always found that getting on to (or near to) the crest of the ridge as soon as the rock appears is the best option.

The upper section of Y Gribin

During the time we’d been making our way up from Ogwen wind-blown cloud sometimes descended on the higher Glyder peaks,  this quickly disappeared before the next batch arrived, all pushed by what seemed like a strengthening keen wind.  Hopefully our arrival on the summits would be timed when the heat of the day burnt off the residue of cloud.  

As height was gained we slithered our way over rock and up steep gullies, I hadn’t done anything like this since my visit to the Cuilin to survey Knight’s Peak last September.  When scrambling isn’t a weekly occurrence it can become quite dramatic in its impact, and we soon found that although this ridge is fairly easy it was enough to thrill.

On the lower section of the rock crest of Y Gribin

Ed on Y Gribin with Llyn Ogwen and Llyn Bochlwyd in the background

In one of the steep gullies on Y Gribin

The arrival on the plateaux heralded a rest from the exposure and excitement, I wanted to survey the critical bwlch for Glyder Fach, this was only a short descent south-east from the point of the top of Y Gribin, while I headed towards the bwlch Ed shot off to visit Glyder Fawr.

The bwlch consists of boulders interspersed amongst grass, the spot I identified as the point of the bwlch was directly under the side of quite a large rock, I measured a height offset of 0.74m from point of critical bwlch to point of placement for the Trimble on the large rock and proceeded to gather six minutes of data.

The Trimble GeoXH 6000 gathering data on a rock 0.74m above the critical bwlch for Glyder Fach, with the jumble of rock named on the map as Castell y Gwynt in the background

Directly above the bwlch is a jumble of rock that culminates in the summit of Castell y Gwynt.  We’d provisionally arranged for me to wait on its summit for Ed as he dashed back and forth to Glyder Fawr.  The hill is a relatively new addition to the Nuttalls listing and makes a fine addition as few hills in Wales can compare to its sudden up thrust of rock.  As I touched its highest point it was another hill ticked off for my 18^th round of the Welsh 2,000ft’s, just another 29 to go.

Many of my previous ascents had resulted from this hill being included in the Nuttalls list.  This was due to a number of basic levelling surveys that Dewi Jones and I conducted, all of which had given this hill over 15m of prominence.  This resulted in this hill being surveyed with a Leica Disto A8, this was conducted by John Barnard, Dewi and myself.  The result was forwarded to John and Anne Nuttall and Castell y Gwynt was duly included in their list.  

Gathering data at the summit of Castell y Gwynt

However, the hill remained without an accurate summit height produced by GNSS receiver, and one of the objectives of today’s walk was to do just this.  Therefore, as Ed scampered off to visit the summit of Glyder Fawr, I assessed the summit rocks of Castell y Gwynt and positioned the internal antenna of the Trimble aligned with the high point of the hill and set the equipment to gather data.

As I sat on top I kept a look out on the path heading this way from Glyder Fawr for any sign of young Edward, couldn’t see him anywhere, the first sign was when I saw him half way up the jumble of rock seemingly appearing out of nowhere.

Relaxing at the Castell y Gwynt bwlch

The next surveying objective was the Castell y Gwynt bwlch and we lazed in the sunshine as the Trimble gathered its allotted data.  We then headed toward the even larger boulder strewn summit of Glyder Fach.  Nothing like this exists anywhere else in Wales as boulders of all sizes, arranged in all ways are piled one atop another until the highest point is reached.

The next summit to survey - the boulder strewn Glyder Fach

The highest point is easily identifiable and can be reached by an undignified straddle across the crest of its slightly pointed boulder until the rounded high point is reached.  Ed directed me to the high point as I placed the Trimble down and tried to make sure that its position was firmly on the rock, we then sat below it on its eastern side, the only problem with this was that if the strengthening wind was sufficient to dislodge the equipment it would roll down on the western side, below lay Trimble oblivion as clefts between some of these summit boulders are dark and extremely uninviting, if it was dislodged and fell in to one of these it would probably expire its battery life trying to measure the inner depths of a dark recess!

The Trimble GeoXH 6000 gathering data on the high point of Glyder Fach

Once five minutes of data was collected I thankfully grabbed the Trimble and packed it away safely in its holster bag.  As we set off down, Ed found what looked like the Ordnance Survey datum point for their measurement of this hill.  Glyder Fach is given a spot height of 994m on Ordnance Survey maps, this height has been rounded up from a 993.648m height to bolt in rock that appears in the OS Trig Database. 

The high Eryri peaks from Glyder Fach

We paid the customary visit to the Cantilever rock and took a series of photos before finding the top of the scree path that steeply descends toward Bwlch Tryfan.  By now the sun was giving pleasant warmth and the wind of earlier now no more than a slight breeze, we sat in the sunshine and I scoffed a couple of butties, life was good! I tried getting data from Bwlch Tryfan which would have given an accurate drop value for Tryfan, unfortunately the Trimble never achieved the 0.1m of accuracy required before data is logged, and this was probably due to it being positioned next to a large cairn and the steepness of mountain sides above the bwlch.

The balanced Cantilever rock

The descent back to Ogwen from bwlch Tryfan is pleasant on good paths; we rested close to Llyn Bochlwyd for a few minutes before joining our inward route back to Ogwen.  Six hours and twenty minutes after setting out we arrived back at the car having had a great day in the hills.

Survey Result:

Glyder Fach

Summit Height:  994.3m (converted to OSGM15)

Summit Grid Reference:  SH 65641 58286

Bwlch Height:  919.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 65272 58156

Drop:  74.5m

Dominance:  7.49%

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) (from subsequent Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 65419 58194 (from subsequent Trimble GeoXH 6000 survey)

Drop:  16.0m

Dominance:  1.64%

For details on the 2nd survey of Castell y Gwynt

For further details please consult the Trimble survey spreadsheet click {here}