Mapping Mountains – Hill Reclassifications – Marilyns

Mynydd y Cwm (SJ 073 767) – Submarilyn reclassified to Marilyn

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 forthcoming 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 the hill reclassification appear below:

The name of the hill is Mynydd y Cwm, and it is situated in the Bryniau Clwyd group of hills in the north-eastern part of Wales, and is positioned with the A5151 road to its north and the A55 road to its south, and has the small city of Llanelwy (St Asaph) towards the south-west.

Prior to this hill’s reclassification to Marilyn status it was listed as a Submarilyn with 149m of drop based on the uppermost 305m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map and the 156m bwlch height that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.  

The Leica 530 set-up position during the first bwlch survey of Mynydd y Cwm

As its 149m listed drop was near the benchmark value of 150m it was prioritised for a GNSS survey and this took place on the 2^nd December 2008.  The summit and bwlch of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 with various collection times of data from 15 minutes to one hour taken.  As the resulting drop value was so close to the benchmark of 150m it was decided to re-visit the hill and gather further data.

The Leica 530 set-up position during the first summit survey of Mynydd y Cwm

The second survey was conducted on the 15^th January 2009 by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530, resulting in the average from each survey for the summit and bwlch of this hill to be 304.9m summit height and 154.9m bwlch height, with these values giving this hill 150.0m of drop.

The reclassification of this hill from Submarilyn to Marilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in April 2009.

The full details for the hill are:

Name:  Mynydd y Cwm

OS 1:50,000 map:  116

OS 1:25,000 map:  264, 265

Summit Height:  304.9m (converted to OSGM15)

Summit Grid Reference:  SJ 07307 76734

Bwlch Height:  154.9m (converted to OSGM15)

Bwlch Grid Reference:  SJ 17432 67786

Drop:  150.0m

Myrddyn Phillips (February 2020)