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}