Mapping Mountains – Summit Relocations – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

The Mount (ST 258 848)

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height derived from the OS Trig Database and the bwlch height derived from interpolation of 5m contouring.

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is The Mount and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it has minor roads to its north-west and north-east and the M4 motorway to its south, and is positioned between the city of Caerdydd (Cardiff) to the south-west and Casnewydd-ar-Wysg (Newport) to the north-east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 124m summit height, based on the spot height positioned at ST 25276 84738 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating that the Ordnance Survey 1:50,000 Landranger map dated 1986 has a 127m spot height adjoined to a triangulation pillar and which is positioned at ST 25869 84831.  As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 124m spot height appears on the 1:25,000 Explorer map.

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

Since publication of these P30 lists on Geoff Crowder’s v-g.me website the heights on different scaled Ordnance Survey maps can be cross referenced against a number of sources that are now available online, and 1:25,000 map data is no longer prioritised for summit heights over that of 1:50,000 map data, each is now assessed individually.

The summit height adjoined to the old triangulation pillar 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.

Therefore, the listed summit height of this hill is 127m and this was derived from the 127.247m flush bracket height adjoined to a triangulation pillar that once stood on the summit of this hill and which was destroyed in September 1985, this position is approximately 550 metres eastward from the previously listed summit position where the 124m spot height appears on the Ordnance Survey 1:25,000 Explorer map.  

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  The Mount

OS 1:50,000 map:  171

Summit Height:  127m

Summit Grid Reference (new position):  ST 25868 84839

Bwlch Height:  c 66m

Bwlch Grid Reference:  ST 24800 87551

Drop:  c 61m

Dominance:  48.03%

Myrddyn Phillips (August 2019)