Mapping Mountains – Summit Relocations – 200m Twmpau

 

Pen y Garn (SN 314 371) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Garn (SN 314 371)

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

200m Twmpau - Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Garn and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the A484 road farther to its north and the B4333 road farther to its east, and has the town of Castellnewydd Emlyn (Newcastle Emlyn) towards the north.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 category and listed with a 289m summit height, based on the spot height positioned at SN 31452 37211 that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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.

LIDAR analysis gives the highest ground on this hill as 290.4m positioned at SN 31405 37181.  However, this is a part of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Pen y Garn (SN 314 371)

The height produced by LIDAR analysis to the natural summit of this hill is 289.0m and this is positioned at SN 31415 37188, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, 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.

Therefore, the summit height produced by LIDAR analysis is 289.0m and this is positioned at SN 31415 37188, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 37 metres west south-westward from the previously listed summit position and approximately 10 metres north-eastward from the high point of the raised field boundary. 

 

The full details for the hill are: 

Group:  Mynydd Pencarreg 

Name:  Pen y Garn 

OS 1:50,000 map:  145

Summit Height:  289.0m (LIDAR) 

Summit Grid Reference (New Position):  SN 31415 37188 (LIDAR) 

Bwlch Height:  226.4m (LIDAR) 

Bwlch Grid Reference:  SN 32309 36820 (LIDAR) 

Drop:  62.6m (LIDAR) 

 

Myrddyn Phillips (October 2024)