Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Ynys Hir (SH 566 396) – 30-99m Twmpau addition

There has been an addition to the Twmpau (thirty welsh metre prominences and upward) list with this hill being included in the 30-99m height band.  Accompanying all the 100m height band of hills within the Twmpau are sub lists with the one attached to this list being entitled the 30-99m Sub-Twmpau.

The criteria for 30-99m Twmpau status is all Welsh hills at or above 30m and below 100m in height with 30m minimum drop, whilst the criteria for 30-99m Sub-Twmpau status is all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop.

The details relating to this hill’s addition are retrospective as it was proposed as a possible new P30 by Aled Williams, and subsequently surveyed with the Trimble GeoXH 6000 on the 1^st February 2014.

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.

The hill is in the Moel Hebog group of hills and is placed in the Region of North Wales (Region A, Sub-Region A1) with its Cardinal Hill being Pt. 734m (SH 525 502) 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 woodland that covers this and 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 30-99m Twmpau as the survey with the Trimble GeoXH 6000 produced a summit height of 37.3m (converted to OSGM15), and with an estimated bwlch height of c 3m it gives this hill c 34m of drop.

The full details for the hill are:

Cardinal Hill:  Pt. 734m (SH 525 502)

Summit Height:  37.3m (converted to OSGM15)

Name:  Ynys Hir

OS 1:50,000 map:  124

Summit Grid Reference:  SH 56695 39693

Drop:  c 34m

Beyond the cliffs and vegetation is the summit of Ynys Hir (SH 566 396) which has been confirmed as a 30-99m Twmpau

For details on the survey that confirmed this hill’s 30-99m Twmpau status

Myrddyn Phillips (July 2017)