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

Ynys Hir (SH 566 396) - Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales due to a survey with the Trimble GeoXH 6000.  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 surveyed on the 1^st February 2014 and later appeared in the Moel Hebog group of Dominant hills when published on the Mappingn Mountains site on the 28^th January 2016.

Prior to the survey with the Trimble this hill was unclassified as the Ordnance Survey 1:50,000 Landranger map, 1:25,000 Explorer map and the enlarged mapping hosted on the Geograph website all give the hill an uppermost 20m ring contour, implying that its height is not sufficient for P30 status and consideration as a Dominant hill.  However, it was Aled Williams who first proposed that this hill may attain P30 status and it was subsequently surveyed in his company.

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 communities of Porthmadog to its south and Tremadog to its north north-west, with the A 487 road to its immediate south.  The hill can be visited from this road where a lay-by gives access through a gate into the woodland that covers this and the other adjacent small hills.

The name of the hill is Ynys Hir and as its name implies it forms an island, which is now landlocked, it is included as a Dominant hill as the survey with the Trimble GeoXH 6000 produced a summit height of 37.3m, and with an estimated bwlch height of c 3m it gives this hill 91.21% Dominance.

The full details for the hill are:

Group:  Moel Hebog

Name:  Ynys Hir

Dominance:  91.21%

OS 1:50,000 map:  124

Summit Grid Reference:  SH 56695 39693

Summit Height:  37.3m (converted to OSGM15)

Drop Summit to Bwlch:  c 34m

Drop Bwlch to ODN:  c 3m 

Beyond the cliffs and immersed in woodland is the summit of Ynys Hir (SH 566 396) which is now classified as a Dominant hill

For details on the survey that confirmed this hill’s Dominant status

Myrddyn Phillips (February 2017)