Showing posts with label Tryfan. Show all posts
Showing posts with label Tryfan. Show all posts

Wednesday, 22 March 2023

Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru


Tryfan (SH 663 593) – Welsh Highland Sub deletion 

There has been a deletion to the listing of the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Aled Williams. 

Tryfan (SH 663 593) (Photo: Aled Williams)

The criteria for the list that this deletion 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 Tryfan 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 south-east.

When the initial P10 sub list was completed in June 2020 this hill was not included.  Revision of the list based on basic levelling surveys conducted by Myrddyn Phillips was completed the following month and this hill was then listed with 10.0m of drop, based on a basic levelling survey conducted on the 01.05.98, and listed with a 910m summit height that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map and a 900m bwlch height, based on the basic levelling survey result compared to the summit spot height.

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

Due to the marginal nature in both listed drop and the accuracy of the surveying method that this was obtained from, this hill was prioritised for a Trimble GeoXH 6000 survey and this has now taken place resulting in its deletion from sub status. 

A precarious position for a survey - Trimble attached to a dog lead and held in situ (Photo: Aled Williams)

Therefore, the deletion of this hill from Welsh Highland Sub status is due to a Trimble GeoXH 6000 survey, resulting in a 910.8m summit height and a 901.6m bwlch height, with these values giving this hill 9.2m of drop, which is insufficient for it to be classified as a Welsh Highland Sub.

 

The full details for the hill are: 

Group:  Glyder Fawr

Name:  Tryfan

OS 1:50,000 map:  115

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 

 

For the additions, deletions and reclassifications to the Welsh Highlands – Uchafion Cymru reported on Mapping Mountains please consult the following Change Registers:

 

Welsh Highland P15s

 

Welsh Highland Subs

 

Aled Williams and Myrddyn Phillips (March 2023)

  

Sunday, 19 March 2023

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


Tryfan (SH 664 594) 

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 a Trimble GeoXH 6000 survey conducted by Aled Williams. 

Tryfan (SH 664 594) (Photo: Aled Williams)

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 Tryfan 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 south-east.

When the P10 sub list was compiled this hill was listed with 12.6m of drop, based on a basic levelling survey conducted by Myrddyn Phillips on the 01.05.98, with the summit height listed as 899m and the bwlch height as 886m, with both heights based on interpolation of contouring that appear on contemporary Ordnance Survey maps. 

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

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 900.0m summit height positioned at SH 66422 59485, 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 set-up position at the summit of Tryfan (SH 664 594) (Photo: Aled Williams)

The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 664 594) (Photo: Aled Williams) 

Therefore, the new listed summit height of this hill is 900.0m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 66422 59485 and is 1.0m higher than its previously listed height of 899m which was based on the drop value ascertained from a basic levelling survey compared to Ordnance Survey map contouring, and is 10.0m higher than the uppermost contour on the contemporary Ordnance Survey 1:25000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Glyder Fawr

Name:  Tryfan

OS 1:50,000 map:  115

Summit Height (New Height):  900.0m (converted to OSGM15)

Summit Grid Reference:  SH 66422 59485  

Bwlch Height:  887.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 66385 59441

Drop:  12.5m

 

Aled Williams and Myrddyn Phillips (March 2023)

 

 

  

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