Wednesday, 14 December 2016

Mapping Mountains – Hill Reclassifications – Y Pedwarau

Moel Tryfan (SH 517 559) - 400m Sub-Pedwar addition

There has been a new 400m Sub-Pedwar added to the list by analysis of LIDAR data by Aled Williams.  The hill is one that Aled first proposed as a prospective 400m Sub-Pedwar approximately two years ago and it then waited to be Trimbled, but as of now this has not occurred and in the meantime as LIDAR data is proving highly accurate we are using the data that Aled has obtained.  The 400m Sub-Pedwarau are the Welsh hills at or above 400m and below 500m in height with a drop between 20m and below 30m.

The hill is situated in the group of hills known as Moel Hebog with its Cardinal Hill being Mynydd Mawr (SH 539 546) and is placed in the Region of North Wales (A-1).  The hill is positioned above the small communities of Nantlle to its south and Groeslon towards its west, and is immediately above the remains of the Moel Tryfan Slate Quarry and the Alexandra Slate Quarry, and can be easily accessed from either a track leading up through the slate spoil from the south or a track from the north-west that contours round the northerly part of the hill before heading toward its summit.

The name of the hill is Moel Tryfan and this name is shared with its higher adjacent summit positioned at SH 515 561 which is 429.0m in height.  The hill is of interest as it is only now listed as a 400m Sub-Pedwar through the quarrying activities of past years, as the quarry now separates the 400m Sub-Pedwar from its 429.0m higher adjacent peak which is already listed as a Pedwar.  In essence the new 400m Sub-Pedwar consists of a man-made natural summit as the quarrying activity has created two new bylchau and split the summit plateau of Moel Tryfan in two parts.

The current Ordnance Survey map details give this hill an uppermost 400m ring contour that has no spot height and bwlch contours that are not continuous due to the remains of the quarry, and which are either between 380m – 390m or 390m – 400m. 

Aled’s analysis of LIDAR data gives the hill the following details:

Moel Tryfan

Summit Height:  405.4m

Summit Grid Reference:  SH 51781 55927

Bwlch Height:  383.9m

Bwlch Grid Reference:  SH 51523 55909

Drop:  21.5m

With the alternate bwlch position to the north at SH 52022 56309 as 372.9m in height.

Therefore, the 405.4m LIDAR data produced for the summit position at SH 51781 55927 and the 383.9m LIDAR data produced for the bwlch position at SH 51523 55909 is sufficient for this hill to be included in the list of 400m Sub-Pedwarau with 21.5m of drop, and therefore Moel Tryfan is included in the listing of 400m Sub-Pedwar hills and the list of the Y Pedwarau will be updated accordingly.  The list of Pedwar hills is available from the Haroldstreet website.

The full details for the hill are:

Cardinal Hill:  Mynydd Mawr

Summit Height:  405.4m (LIDAR data)

Name:  Moel Tryfan

OS 1:50,000 map:  115

Summit Grid Reference:  SH 51781 55927 

Drop:  21.5m (LIDAR data)

The list of additions, reclassifications and deletions from the 400m Sub-Pedwar list since the 1st edition of the Y Pedwarau was published by Europeaklist are as follows:


Moel Tryfan (LIDAR data) (SH 517 559) 21.5m drop



Looking across at the man-made northern bwlch with the lower slopes of the new 400m Sub-Pedwar of Moel Tryfan on the right

Myrddyn Phillips and Aled Williams (December 2016)

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