Thursday 9 February 2023

Mapping Mountains – Trimble Surveys – Glyder Fawr


26.12.22  Tryfan (SH 664 594) and Tryfan (SH 663 593) 

It had been nearly eleven years since I had last stood on the summit of Tryfan.  The previous occasion had been my sixth ascent, made all the more memorable from the alpine-like conditions that I encountered as I tackled the mountain’s celebrated north ridge.  Today would be reminiscent of that experience, albeit with milder conditions, but would also be shared in the company of my oldest friend, Gwion Owens, who had climbed Tryfan only once before in the 1990s via our planned route. 

Early morning looking east (Photo: Aled Williams) 

A few weeks earlier, Myrddyn Phillips had loaned me the use of his Trimble over the winter months, with the idea being for me to measure a number of marginal candidates in Eryri for P10 Sub-Top status associated with our co-authored Welsh Highlands list.  Unbeknownst to Gwion, I had already planned to take advantage of his presence by asking him to become my surveying assistant for the day; a role he would perform admirably and with much stoicism! 

Looking down on Llyn Ogwen (Photo: Aled Williams)

Arriving just after dawn, we noticed that the upper portion of the mountain had received an overnight dusting of snow, with our surveying objectives, the north and south peaks, looking forlorn and formidable.  Our enthusiasm further ebbed as we booted up in the cold recesses of the car park, but as we climbed up through the maze of boulders to the start of the ridge we had warmed up considerably. 

Gwion on The Cannon (Photo: Aled Williams)

The first of many scrambling challenges then presented itself; a narrow crack that provided a line of weakness in an otherwise castellated bluff. Seeing this feature brought back memories of previous ascents and the awkward step up to attain the crack reminded me of how flexible I once was!  Having squeezed up to the next level a succession of further obstacles were then overcome until we arrived at the famous jutting rock affectionally referred to as The Cannon by the climbing and walking fraternities.  A customary photograph was mandated and Gwion gingerly crawled up the slab to reach its pinnacle.  However, a vicious south-westerly made a standing pose out of the question and so we settled on a crouching thumbs up instead! 

Typical territory on the north ridge of Tryfan (Photo: Aled Williams)

The next scramble was a harbinger of what was to come.  A mixture of snow and ice was now omnipresent on the key hand and footholds and the section leading up to the north top of the mountain looked a dangerous prospect.  Carefully negotiating exposed sections with cold hands and tired limbs we gradually made progress and arrived at the top of a gully. 

Gathering data at the northerly summit of Tryfan (Photo: Aled Williams)

A short icy section then led us to the gap between the summit of Tryfan and its north peak.  This spot was one of our surveying objectives, but we decided to first survey the summit of the north top.  Gwion was given a crash course in the use of an Abney level, he then proceeded to identify the highest point to be surveyed by the Trimble.  The ice, snow and wind made placing the Trimble a hazardous affair and data collection was performed by me sheltering beneath the pinnacle with a dog lead attached to the Trimble, thus ensuring that Myrddyn’s pride and joy did not plunge into the abyss of Cwm Tryfan. 

Delicately balanced but attached to a rucksack via its dog lead (Photo: Aled Williams)

Next to be surveyed was the critical col.  The wedged-like shape of this spot at the top end of a narrow gully proved difficult for the Trimble and a cold vigil awaited us as the Trimble gradually attained its 10cm accuracy level.  Four other adventurers passed us while we waited, asking us if we were alright; no doubt slightly perplexed as to why we were sitting in such a spot with a tape measure and an unusual yellow-coloured piece of kit! 

The northerly summit of Tryfan (Photo: Aled Williams)

Having collected data we then made our final push to the summit of Tryfan and visited those faithful biblical monoliths.  The views were inspiring and we pondered whether Tryfan was the most impressive mountain of southern Britain. 

The monoliths of Adam and Eve at the summit of Tryfan (Photo: Aled Williams)

However, our work was far from finished.  The south top remained to be surveyed and so we headed down to the notch that connected the two peaks.  Recent analysis of LIDAR data that I had undertaken had indicated that the prominence of the south top was less than 10m, but inspection of the terrain at the col revealed deep gaps between the boulders and the bedrock, which would not have been modelled by LIDAR. 

A flash of light on a winter scene (Photo: Aled Williams)

The conditions were not conducive for a prolonged assessment, but what was perceived as the most optimal position was selected with an offset of 5ocm taken between the receptor of the Trimble and what was deemed to be the bedrock.  Gwion duly assisted by counting down the two minutes of data collection as he stood among the freezing rocks.  In eleven years of surveying hills and mountains, these were the worst conditions I had operated in. 

The southerly summit of Tryfan (Photo: Aled Williams)

We then headed up to the summit of the ice-covered south peak.  This proved to be a flat-topped rock broken up by several deep fissures.  An almighty drop presented itself on the north side and so we decided that the saftest approach for surveying would involve me lying face-down on the highest point with one foot wedged in a fissure and the Trimble attached to my arm via the dog lead!  There was method to this madness, as the survey went smoothly albeit uncomfortably. 

A precarious position at the top of the southerly summit of Tryfan (Photo: Aled Williams)

Once the measuring was completed, we slipped and slided down the southern ridge, looping back around the mountain to the awaiting car.  It had been an exciting day out among spectacular scenery; all that remained was the drive home in time for our traditional Boxing Day celebrations at the local pub.

Aled Williams (December 2022) 

 

Survey Result: 

 

Tryfan

Summit Height:  900.0m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SH 66422 59485

Bwlch Height:  887.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 66385 59441

Drop:  12.5m

Dominance:  1.39%

 

 

Tryfan

Summit Height:  910.8m (converted to OSGM15)

Summit Grid Reference:  SH 66393 59332

Bwlch Height:  901.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 66378 59359

Drop:  9.2m (Welsh Highland Sub deletion)

Dominance:  1.01%


 

For further details please consult the Trimble Survey Spreadsheet

 

  

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