Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

 

Pen Tyrau (SH 837 382) – Welsh Highland Sub addition 

There has been an addition 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. 

Pen Tyrau (SH 837 382).  Photo: Aled Williams

The criteria for the list that this addition 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 Aled Williams and Myrddyn Phillips

The name the hill is listed by is Pen Tyrau, and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road and the A4212 road to its north, and has the town of Y Bala towards the east south-east. 

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

The status of this hill has a convoluted history as it was originally listed with less than the required 10m minimum drop to qualify for sub status, and then included when the initial P10 sub list was completed in June 2020 and listed with 10.4m of drop, based on a basic levelling survey conducted by Myrddyn Phillips on the 14.09.98, and listed with a 697m summit height a 687m bwlch height, with an accompanying note stating that analysis of numerical data on various scales of Ordnance Survey maps give this hill an estimated c 9m of drop.  Therefore, it was included as a Welsh Highland Sub when the drop value of the subs was agreed upon and revised in July 2020. 

The Trimble GeoXH 6000 gathering data at the summit of Pen Tyrau.  Photo: Aled Williams

The hill was subsequently analysed via LIDAR by Aled Williams, resulting in a 697.8m summit height and a 688.1m bwlch height, with these values giving this hill 9.7m of drop, which is insufficient for it to be classified as a Welsh Highland Sub.  However, with the drop value relatively close to the qualifying criterion of 10m this hill was prioritised for a survey with the Trimble GeoXH 6000. 

The Trimble GeoXH 6000 gathering data at the bwlch of Pen Tyrau.  Photo: Aled Williams

Therefore, the addition of this hill to Welsh Highland Sub status is due to a Trimble GeoXH 6000 survey, resulting in a 697.4m summit height and a 687.4m bwlch height, with these values giving this hill 10.0m of drop, which is sufficient for it to be reinstated as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Arenig Fawr

Name:  Pen Tyrau           

OS 1:50,000 map:  124, 125

Summit Height:  697.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 83737 38250 (Trimble GeoXH 6000)

Bwlch Height:  687.4m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 83601 38142 (Trimble GeoXH 6000)   

Drop:  10.0m (Trimble GeoXH 6000) 

 

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 (November 2024)

Mapping Mountains – Trimble Surveys – Arenig Fawr

28.07.24  Pen Tyrau (SH 837 382) 

The early morning start provided negligible respite from the summer heat.  I stood forlornly upon the bank of Llyn Arenig Fawr as I eyed up the steep sections of the arm that would take me to Bwlch Blaen Nant.  The anxiety lapsed as I took in the beauty of the scene; abstract reflections of a rugged mountain framed by a cloudless sky, the calm intercepted momentarily by the shrieking calls of peregrine falcons.

The morning view from Llyn Arenig Fawr.  Photo: Aled Williams 

Ahead lay Pen Tyrau, which was the surveying objective of the day, having recently been deleted as a P10 Sub-Top within The Welsh Highlands list.  Analysis of LIDAR data indicated that the prominence of the hill only reached 9.7m, which is 30cm short of the qualifying threshold of 10m.  Armed with Myrddyn’s Trimble GeoXH 6000, my intention was to confirm the hill’s status by obtaining an accurate value for its drop.

Looking toward the summit area of Pen Tyrau.  Photo: Aled Williams 

Despite its modest credentials as a separate hill, the top caps an extensive crag-rimmed plateau that forms the north-eastern projection of Arenig Fawr.  This promontory is known locally as Pen Tyrau, a name that has suffered slippage on OS maps over the years.  Its elevated position is a wild place consisting of moorland dappled with small pools and dotted with rough outcrops and small glacial erratics. Having traversed through the bogs of Blaen Nant, I soon found myself standing beside the summit cairn where data was to be collected.

The view from the summit of Pen Tyrau.  Photo: Aled Williams

Surveying was not made easy by the clouds of midges that were swarming the plateau.  Having completed the first survey, I begrudgingly decided to take another set of measurements from a nearby rock that the Abney level had deemed to be close in height to the cairned high point.  As I waited for the Trimble to complete its measuring, I looked out to Arenig Fach and noted the similarities between the character and topography of that hill to that of Pen Tyrau.

The Trimble GeoXH 6000 gathering data at the summit of Pen Tyrau.  Photo: Aled Williams

I headed to the hill’s bwlch for the final survey of the day.  A characteristic of such places is the tricks they play on the eyes, with ups looking like downs and vice versa depending on where one stands.  This bwlch proved to be no exception and I unashamedly used the Trimble as a hand-held GPS to bring me to the point LIDAR had determined to be both the trough in the hill-to-hill line and the crest in the valley-to-valley traverse.

Gathering data at the bwlch of Pen Tyrau.  Photo: Aled Williams

The end of the surveying brought a sudden end to the veritable feast that the midges were enjoying.  I escaped via my inward route to Bwlch Blaen Nant and stopped atop the crags of Y Castell to admire the view down into the waters of Llyn Arenig Fawr.  Behind me towered the upper ridge of Arenig Fawr, which the midday sun would not entice me to visit.

Arenig Fawr from the descent of Pen Tyrau.  Photo: Aled Williams

Aled Williams (July 2024)

 

Survey Result: 

 

Pen Tyrau

Summit Height:  697.4m (converted to OSGM15)

Summit Grid Reference:  SH 83737 38250

Bwlch Height:  687.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 83601 38142

Drop:  10.0m (Welsh Highland Sub addition)

Dominance:  1.44%

 

For further details please consult the Trimble Survey Spreadsheet

 

 

 

  

Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru

DUE TO A TRIMBLE GEOXH 6000 SURVEY THIS HILL HAS SUBSEQUENTLY BEEN REINSTATED TO WELSH HIGHLAND SUB STATUS

Pen Tyrau (SH 837 382) – 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 LIDAR analysis conducted by Aled Williams. 

LIDAR image of Pen Tyrau (SH 837 382)

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 Pen Tyrau, and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road and the A4212 road to its north, and has the town of Y Bala towards the east south-east.

When the initial P10 sub list was completed in June 2020 this hill was listed with 10.4m of drop, based on a basic levelling survey conducted by Myrddyn Phillips on the 14.09.98, and listed with a 697m summit height a 687m bwlch height, with an accompanying note stating that analysis of numerical data on various scales of Ordnance Survey maps give this hill an estimated c 9m of drop.  Therefore, it was included as a Welsh Highland Sub when the drop value of the subs was agreed upon and revised in July 2020. 

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

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the deletion of this hill from Welsh Highland Sub status is due to LIDAR analysis, resulting in a 697.8m summit height and a 688.1m bwlch height, with these values giving this hill 9.7m of drop, which is insufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Arenig Fawr

Name:  Pen Tyrau

OS 1:50,000 map:  124, 125

Summit Height:  697.8m (LIDAR)

Summit Grid Reference:  SH 83744 38244 (LIDAR)

Bwlch Height:  688.1m (LIDAR)

Bwlch Grid Reference:  SH 83602 38147 (LIDAR)   

Drop:  9.7m (LIDAR) 

 

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 (July 2023)