Mapping Mountains – Hill Reclassifications – 100m Twmpau

Cae Nesaf Glanrafon (SH 317 387) – 100m Sub-Twmpau addition

There has been an addition to the 100m Twmpau due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

100m Twmpau - Welsh hills at and above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at and above 100m and below 200m 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.

Prior to LIDAR analysis this hill was listed with an estimated c 18m of drop based on the 107m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 89m based on bwlch contouring at 5m intervals and between 85m – 90m on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

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

The bounded land where the summit of this hill is situated is named Cae Nesaf Glanrafon on the Tithe map and it is adjoined to the Pen Llŷn group of hills, which is situated in the north-west part of North Wales (Region A, Sub-Region A1), and is positioned to the immediate south of the B 4354 road and north-east of the A 497 road and has the small community of Nefyn to its north-west.

If wanting to visit the hill permission to do so should be sought as it is not a part of designated open access land and has no rights of way on it.

The addition of Cae Nesaf Glanrafon to 100m Sub-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 LIDAR analysis gives the hill the following details:

Cae Nesaf Glanrafon

Summit Height:  107.4m

Summit Grid Reference:  SH 31707 38723

Bwlch Height:  86.7m

Bwlch Grid Reference:  SH 31781 38801

Drop:  20.7m

LIDAR image of Cae Nesaf Glanrafon

Therefore, the 107.400m LIDAR analysis for the summit position at SH 31707 38723 and the 86.662m LIDAR analysis for the bwlch position at SH 31781 38801 gives this hill 20.738m of drop, which is sufficient for 100 Sub-Twmpau status.

The full details for the hill are:

Group:  Pen Llŷn

Name:  Cae Nesaf Glanrafon

Summit Height:  107.4m (LIDAR)

Summit Grid Reference:  SH 31707 38723 (LIDAR)

OS 1:50,000 map:  123

Drop:  20.7m (LIDAR)

Myrddyn Phillips (April 2018)