Mapping Mountains – Hill Reclassifications – 200m Twmpau

Mynydd Pant y Carneddau (SN 661 997) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been a reclassification of a hill in the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mynydd Pant y Carneddau (SN 661 997)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Mynydd Pant y Carneddau, and this was derived from the Tithe map, and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its south and the A493 road farther to its south-east, and has the town of Machynlleth towards the east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 28m of drop, based on the 246m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 218m bwlch height, based on interpolation of 10m contouring between 210m – 220m. 

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

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the reclassification of this hill from 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 247.8m summit height and a 216.6m bwlch height, with these values giving this hill 31.2m of drop, which is sufficient for it to be classified as a 200m Twmpau. 

 

The full details for the hill are: 

Group:  Tarren y Gesail 

Name:  Mynydd Pant y Carneddau 

OS 1:50,000 map:  135

Summit Height:  247.8m (LIDAR) 

Summit Grid Reference:  SN 66184 99721 & SN 66185 99722 (LIDAR) 

Bwlch Height:  216.6m (LIDAR) 

Bwlch Grid Reference:  SN 66410 99840 (LIDAR) 

Drop:  31.2m (LIDAR) 

 

Myrddyn Phillips (June 2025)