Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Ynys Glog (SH 596 398) - Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales due to detail included on the Ordnance Survey enlarged mapping hosted on the Geograph website and which was first spotted by Aled Williams.  This has resulted in the hill being added to the Dominant list.  With the criteria for inclusion to this list being those Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The details relating to this hill’s inclusion as a Dominant hill are retrospective as it was added to the list shortly after Aled first proposed it as a new P30 in February 2014, and later appeared in the Moelwynion group of Dominant hills when published on Mapping Mountains on the 25^th February 2016.

Prior to Aled proposing this hill as a new P30 and its subsequent inclusion as a Dominant hill, it was not classified as contouring on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map implied that the hill did not have the required minimum 30m of drop to be considered for P30 and Dominant status.

The hill is in the Moelwynion group of hills and is placed in the Region of North Wales (Region A, Sub-Region A1) and is situated between the towns of Porthmadog to the west south-west and Penrhyndeudraeth to the east south-east.

The hill is not on open access land and therefore permission to visit should be sought.  For those wishing to do so the ascent is through undergrowth next to stunted deciduous trees to a summit which is slightly laid back from a large drop to fields below.

The name of the hill is Ynys Glog, and it was included as a Dominant hill based on detail from the Ordnance Survey enlarged mapping hosted on the Geograph website which gives the hill a 42m summit spot height and bwlch contouring between 5 – 10m, with an estimated bwlch height of c 8m, these values gave the hill c 34m of drop and 80.95% Dominance.  The hill has subsequently been surveyed using the Trimble GeoXH 6000 resulting in a 40.6m (converted to OSGM15) summit height and a 7.9m (converted to OSGM15) bwlch height, giving this hill 32.7m of drop and 80.44% Dominance.

The full details for the hill are:

Group:  Moelwynion

Name:  Ynys Glog

Dominance:  80.44%

OS 1:50,000 map:  124

Summit Grid Reference:  SH 59647 39826

Summit Height:  40.6m (converted to OSGM15)

Drop Summit to Bwlch:  32.7m

Drop Bwlch to ODN:  7.9m (converted to OSGM15) 

Ynys Glog (SH 596 398) now listed as a Dominant hill

For details on the survey that confirmed this hill’s Dominance

Myrddyn Phillips (April 2017)