Mapping Mountains – Hill Reclassifications – 200m Twmpau

Tŵr Glas (SH 672 164) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification to the 200m Twmpau list due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

200m Twmpau - Welsh hills at and above 200m and below 300m in height with 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 and above 200m and below 300m in height with 20m and more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

This hill was listed in the Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website as it did not meet the criteria then used for the main P30 list; however this list has now been standardised and interpolated heights and drop values also included, resulting in this hill being listed with an estimated c 30m of drop, based on the 227m summit spot height that appears on Harvey maps and an estimated bwlch height of c 197m based on bwlch contouring between 190m – 200m.  The details for this hill were later amended when the Ordnance Survey Interactive Coverage Map hosted on the Geograph website became available online and it was then listed with an estimated c 32m of drop based on the 228m summit spot height appearing on this map and re-interpolation of bwlch contouring giving an estimated bwlch height of c 196m.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The name of the hill is Tŵr Glas and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), it is positioned overlooking the A 493 road which is to its north-west and has the small community of Arthog towards the south-west and the town of Dolgellau towards the east.

The summit and southern section of the hill is a part of designated open access land with a public footpath approaching the hill from the west probably being the most convenient ascent route, this follows the lower northern section of the hill before entering the open access land toward the east of the summit.

The confirmation of the reclassification of Tŵr Glas to 200m Twmpau status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The 1m DTM LIDAR analysis gives the hill the following details:

Name:  Tŵr Glas

Summit Height:  227.4m

Summit Grid Reference:  SH 67218 16437

Bwlch Height:  193.6m

Bwlch Grid Reference:  SH 67439 16279

Drop:  33.8m

LIDAR image of Tŵr Glas

Therefore, the 227.4m LIDAR analysis for the summit position at SH 67218 16437 and the 193.6m LIDAR analysis for the bwlch position at SH 67439 16279 gives this hill 33.8m of drop, which confirms its reclassification to 200m Twmpau status.

The full details for the hill are:

Group:  Cadair Idris

Name:  Tŵr Glas

OS 1:50,000 map:  124

Summit Height:  227.4m (LIDAR)

Summit Grid Reference:  SH 67218 16437 (LIDAR)

Bwlch Height:  193.6m (LIDAR)

Bwlch Grid Reference:  SH 67439 16279 (LIDAR)

Drop:  33.8m (LIDAR)

Myrddyn Phillips (June 2018)