Mapping Mountains – Summit Relocations – Yr Uchafion and 600m Twmpau

Cefn Gwyntog (SH 975 266)

There has been a Summit Relocation to a hill that is listed in the Yr Uchafion and the 600m Twmpau, with the summit height and drop of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips which took place on the 16^th August 2018.

Cefn Gwyntog (SH 975 266)

The criteria for the two listings that this summit relocation applies to are:

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

600m Twmpau – Welsh hills at or above 600m and below 700m in height that have 30m minimum drop, with an accompanying sub category entitled the 600m Sub-Twmpau consisting of all Welsh hills at or above 600m and below 700m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips.

The name of the hill is Cefn Gwyntog, and it is adjoined to the Y Berwyn range of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned to the north of Llyn Efyrnwy (Lake Vyrnwy) and has the town of Y Bala towards the north north-west.

As the summit of the hill is a part of designated open access land it can be approached from various directions.  However, the easiest approach is from the north where a track contours the moorland and a narrow path leaves this track toward an old gate and continues toward the summit of this hill.

When this hill was first included in the lists that would later be known as the Yr Uchafion and the 600m Twmpau the summit position was given to where the 615m spot height appeared on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day, this is at SH 97602 26597.  This position is close to where a small cairn with an upright stone is placed on the ground.

However, having visited this summit 19 times prior to the survey with the Trimble GeoXH 6000 I knew that there were two other positions that vied for the highest point of this hill, and therefore I wanted to conduct three separate surveys from the area of its summit.

The results from these three surveys are given below:

1^st survey:  613.766m at SH 97596 26696

2^nd survey:  613.299m at SH 97604 26598

3^rd survey:  613.104m at SH 97655 26618

The first survey was to featureless ground two metres from where the narrow path crosses the summit area of this hill.

Gathering data at the summit of Cefn Gwyntog with the old summit position in the right background of this photograph

The second survey was to the highest ground close to where the small cairn with an upright stone is placed, and within two metres matches the position of the 615m spot height.

Gathering data during the second summit survey on Cefn Gwyntog with the new summit position of this hill in the left centre background of this photograph

The third survey was to ground beside a small cairn on the eastern part of the uppermost 610 metre ring contour that appears on contemporary Ordnance Survey maps.

Gathering data during the third summit survey on Cefn Gwyntog

The 613.8m summit height produced by the Trimble GeoXH 6000 survey and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website showing the new summit position in relation to where the spot height is positioned. 

The summit height produced by the Trimble GeoXH 6000 survey is 613.8m and is positioned at SH 97596 26696, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 100 metres north from where the old listed summit is positioned.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Y Berwyn

Name:  Cefn Gwyntog

OS 1:50,000 map:  125

Summit Height:  613.8m (converted to OSGM15)

Summit Grid Reference (new position):  SH 97596 26696

  

Bwlch Height:  587.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 97493 27338

Drop:  26.7m (converted to OSGM15)

For details on the survey that confirmed the summit relocation of this hill

Myrddyn Phillips and Aled Williams (January 2019)