Tuesday, 21 February 2017

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


Geirth Mawr (SH 535 393) - Dominant deletion

There has been a deletion 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.  This has resulted in the hill being taken out of 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 deletion as a Dominant hill are retrospective as it did not appear in the Moel Hebog group of hills when published on Mapping Mountains on the 28th January 2016.

The hill had been listed in the ‘Hills to be surveyed’ sub-list that accompanied the original Welsh P30 lists when published on Geoff Crowder’s v-g.me website, however when drop values were added to the hand written Master List this hill’s details were re-evaluated and it was catalogued with c 30m of drop based on a summit height of c 58m and a bwlch height of 28m, these values were sufficient for it to be included in the original listing of Y Trechol – The Dominant Hills of Wales with 30m of drop and 51.72% Dominance.

The hill is in the Moel Hebog group of hills and is placed in the Region of North Wales (Region A, Sub-Region A1) and is situated between the small communities of Pentrefelin to its west north-west and Penmorfa to its north-east, with the town of Porthmadog situated to its east.

The hill can be relatively easily accessed from its north-west starting from the A 497 as it makes its way from Porthmadog to Cricieth, the ascent is through deciduous woodland but is not on open access land so permission to visit should be sought.

The name of the hill is Geirth Mawr and it has been deleted from the Dominant list as the Ordnance Survey enlarged mapping hosted on the Geograph website gives the hill a summit spot height of 56m and with a 28m spot height appearing on the area of the connecting bwlch on Ordnance Survey 1:25,000 Explorer maps, it gives this hill 28m of drop, which is insufficient for it to qualify as a Dominant hill.


The full details for the hill are:

Group:  Moel Hebog

Name:  Geirth Mawr

Dominance:  N/A

OS 1:50,000 map:  124

Summit Grid Reference:  SH 53512 39361

Summit Height:  56m

Drop Summit to Bwlch:  28m

Drop Bwlch to ODN:  28m 


Myrddyn Phillips (February 2017)




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