Mapping Mountains – Hill Reclassifications – 500m Twmpau

Craig Stwlan (SH 667 446) – 500m Sub-Twmpau addition

There has been an addition to the listing of the 500m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Aled Williams. 

The Trimble GeoXH 6000 gathering data at the summit of Craig Stwlan (SH 667 446) (Photo: Aled Williams)

The criteria for the list that this addition applies to are:

500m Twmpau - Welsh hills at or above 500m and below 600m in height with 30m minimum drop, with an accompanying sub list entitled the 500m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains. 

The 500m Twmpau by Myrddyn Phillips

The name the hill is listed by is Craig Stwlan and it is adjoined to the Moelwyn Mawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A2), and it is positioned with the B4410 road to its south-west, the A487 road to its south and the A496 road to its east, and has the town of Blaenau Ffestiniog towards the east north-east.

When the list that became known as the 500m Twmpau was first compiled, this hill was listed with an estimated c 20m of drop, based on the 568m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 548m bwlch height, based on interpolation of 10m contouring between 540m – 550m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

The hill was subsequently deleted from 500m Sub-Twmpau status due to initial LIDAR analysis, resulting in a 568.2m summit height and a 548.5m bwlch height, with these values giving this hill 19.7m of drop.  However, the hill has now been surveyed with the Trimble GeoXH 6000 and it is this result that is being prioritised.

Therefore, the addition of this hill to 500m Sub-Twmpau status is due to a Trimble GeoXH 6000 survey, resulting in a 568.4m summit height and a 548.3m bwlch height, with these values giving this hill 20.1m of drop, which is sufficient for it to be classified as a 500m Sub-Twmpau.

 

The full details for the hill are:

Group:  Moelwyn Mawr

Name:  Craig Stwlan

OS 1:50,000 map:  124

Summit Height:  568.4m (converted to OSGM15)

Summit Grid Reference:  SH 66736 44654

Bwlch Height:  548.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 66693 44717

Drop:  20.1m

 

Myrddyn Phillips (March 2023)