Mapping Mountains – Summit Relocations – Y Pedwarau – The 400m Hills of Wales

Mynydd Pen y Fan (SO 191 021)

There has been a Summit Relocation to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Aled Williams.

LIDAR image of Mynydd Pen y Fan (SO 191 021)

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

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, the list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

The name the hill is listed by is Mynydd Pen y Fan 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 is positioned with the A4046 road to its north-east, the A4048 road to its west and the A467 road towards the south-east, and has the town of Coed Duon (Blackwood) towards the south.

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was listed with 56m of drop based on the 409m summit spot height adjoined to a 409.248m flush bracketed triangulation pillar which is positioned at SO 19201 02093 and a 353m bwlch height.

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

When the Y Pedwarau- The 400m Hills of Wales list was published on Mapping Mountains the summit position for this hill was given as the ten figure grid reference in the OS Trig Database adjoined to the flush bracket; SO 19201 02093.

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 summit image of Mynydd Pen y Fan

The summit height and position produced by LIDAR analysis is 407.2m at SO 19197 02179, and this 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 it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or 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 that is judged to be a relatively recent man-made construct.

The 407.2m summit height produced by LIDAR analysis for this hill is at odds with the 409.248m flush bracket height as the triangulation pillar is not positioned on a plinth, and if this height is accurate natural ground at its base would be approximately 408.9m in height.  The discrepancy is due to either a flush bracket height typo or subsidence due to the summit area being in the vicinity of old mine workings.  

Therefore, the new summit height for this hill is 407.2m and is positioned at SO 19197 02179, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and is approximately 90 metres northward from where the previously listed summit is positioned. 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Mynydd Pen y Fan

OS 1:50,000 map:  171

Summit Height:  407.2m (LIDAR)

Summit Grid Reference (new position):  SO 19197 02179 (LIDAR) 

 

Bwlch Height:  352.3m (LIDAR)

Bwlch Grid Reference:  SO 18568 03172 (LIDAR)

Drop:  54.9m (LIDAR)

Aled Williams and Myrddyn Phillips (April 2020)