Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Glan y Morfa (SH 438 679) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau

There has been a reclassification to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Glan y Morfa (SH 438 679)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Glan y Morfa and this was derived from the Tithe map, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north and the A4421 to its south-east, and has the village of Llangaffo towards the north-east. 

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 27m of drop based on twin tops both with a 59m summit spot height (59m at SH 43811 67899 on the Ordnance Survey 1:25,000 Explorer map and 59m at SH 45087 68972 on the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map) and a bwlch height of 32m that appears as spot height on the Ordnance Survey 1:25,000 Explorer map. 

LIDAR summit image of Glan y Morfa

However, just to the north of where the 32m bwlch spot height is positioned is a railway cutting and it was not until LIDAR became available that an accurate height for this and the summit could be determined.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR bwlch image of Glan y Morfa

The details produced by LIDAR analysis for the height and position of the railway cutting and a remaining natural bwlch are given below: 

 

Railway Cutting Bwlch:  27.9m at SH 45679 69377 

Remaining Natural Bwlch:  31.8m at SH 45155 69373 

 

Therefore, the reclassification of this hill from 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 59.2m summit height and a 27.9m bwlch height, with these values giving this hill 31.3m of drop, which is sufficient for it to be classified as a 30-99m Twmpau.  With the caveat that the remaining natural bwlch is 31.8m in height and positioned at SH 45155 69373, which if taken along with the 59.2m summit height would give this hill 27.3m of drop.  But as cuttings on the hill to hill traverse are taken as a part of a hill’s drop value in listings I author this hill is now confirmed as a 30-99m Twmpau. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Glan y Morfa 

OS 1:50,000 map:  114, 115

Summit Height:  59.2m (LIDAR) 

Summit Grid Reference:  SH 43819 67923 (LIDAR) 

Bwlch Height:  27.9m (LIDAR) 

Bwlch Grid Reference:  SH 45679 69377 (LIDAR) 

Drop:  31.3m (LIDAR) 

 

Myrddyn Phillips (March 2021)