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 1st 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.
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)
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