Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Ynys Fadog (SH 564 398) – Double Sub-Twmpau addition

There has been an addition to the Twmpau (thirty welsh metre prominences and upward) list with this hill being included in the Double Sub-Twmpau that accompanies 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.  There is a second sub category that accompanies the 30-99m height band and which is entitled the Double 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, 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, whilst the criteria for Double Sub-Twmpau status is all Welsh hills at or above 20m and below 30m 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, with the current Ordnance Survey 1:50,000 Landranger map, 1:25,000 Explorer map and the enlarged mapping hosted on the Geograph website all giving the hill an uppermost 20m ring contour, which implies that the hill does not have sufficient prominence for P30 status but may attain Double Sub-Twmpau status with 20m or more of drop.

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-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 Fadog and as its name implies it forms an island, which is attached to two higher hills both of which are known as Ynys Hir (SH 566 396 and SH 566 398) which are to the south-east and east respectively, with all three hills now being landlocked, it is included as a Double Sub-Twmpau as the survey with the Trimble GeoXH 6000 produced a summit height of 27.8m (converted to OSGM15) and with an estimated bwlch height of c 3m, it gives this hill c 25m of drop.

The full details for the hill are:

Cardinal Hill:  Pt. 734m (SH 525 502)

Summit Height:  27.8m (converted to OSGM15)

Name:  Ynys Fadog

OS 1:50,000 map:  124

Summit Grid Reference:  SH 56464 39823

Drop:  c 25m

The wooded summit of Ynys Fadog (SH 564 398)

For details on the survey that confirmed this hill’s Double Sub-Twmpau status

Myrddyn Phillips (July 2017)