Mapping Mountains – Hill Reclassifications – Marilyns

Moel Oernant (SH 742 340) – Submarilyn addition

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for this addition appear below:

The name of the hill is Moel Oernant, and it is situated in the Arenig group of hills in the central part of north Wales, and is positioned with the A4212 road to its north and the A470 road to its west, and has the village of Trawsfynydd towards the west north-west.

Prior to the addition of this hill to Submarilyn status it was listed with c 138m of drop, based on the 503m summit height which is adjoined to a triangulation pillar and which appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 365m based on interpolation of 10m contouring between 360m – 370m.

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

The details for this hill were examined during a re-assessment of the 500m Twmpau list and forwarded to the list author of the Marilyns; Alan Dawson.  The area of this hill’s bwlch was assessed using mapping on the OS Maps website.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This mapping has bwlch contours between 360m – 365m with interpolation placing the height of this bwlch at c 362m, resulting in this hill having an estimated drop of c 141m.

Extract from the OS Maps website

These details were forwarded by Myrddyn Phillips via email to the list author of the Marilyns on the 2^nd August 2019, and notification received from Alan Dawson via email on the 17^th August 2019 that the drop was likely to exceed that required for Submarilyn status.

LIDAR image of Moel Oernant (SH 742 340)

The Submarilyn status of this hill has subsequently been confirmed via LIDAR analysis conducted by Aled Williams, resulting in a 502.9m summit height and a 362.2m bwlch height, with these values giving this hill 140.7m drop.

 

The full details for the hill are: 

Name:  Moel Oernant 

OS 1:50,000 map:  124

OS 1:25,000 map:  18

Summit Height:  502.9m (LIDAR) 

Summit Grid Reference:  SH 74223 34006 (LIDAR) 

Bwlch Height:  362.2m (LIDAR) 

Bwlch Grid Reference:  SN 76025 35044 (LIDAR) 

Drop:  140.7m (LIDAR)

 

Myrddyn Phillips (April 2020)