Sunday, 9 July 2017

Mapping Mountains – Hill Reclassifications – 30-99m Twmpau


Pt. 36.9m, Ynys Hir (SH 566 398) – 30-99m 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 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 1st 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 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 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 the hill is listed by is Pt. 36.9m, Ynys Hir and as its name implies it forms an island, which is attached to the higher hill known as Ynys Hir (SH 566 396) which is to the immediate south, with both hills now being landlocked, it is included as a 30-99m Sub-Twmpau as the survey with the Trimble GeoXH 6000 produced a summit height of 36.9m (converted to OSGM15) and a bwlch height of 11.1m (converted to OSGM15), with these values giving this hill 25.8m of drop.


The full details for the hill are:

Cardinal Hill:  Pt. 734m (SH 525 502)

Summit Height:  36.9m (converted to OSGM15)

Name:  Pt. 36.9m, Ynys Hir

OS 1:50,000 map:  124

Summit Grid Reference:  SH 56649 39840

Drop:  25.8m (converted to OSGM15)


The Trimble GeoXH 6000 set-up position at the summit of Pt. 36.9m (SH 566 398).  Phot:  Aled Williams


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

Myrddyn Phillips (July 2017)


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