Mapping Mountains – Summit Relocations – 30-99m Twmpau

Pt. 86.4m (SH 482 875) 

There has been a Summit Relocation to a hill that is listed in the 30-99m 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 Pt. 86.4m (SH 482 875)

The criteria for the list that this summit relocation applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 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. 

The 30-99m Twmpau by Myrddyn Phillips

The hill is being listed by the Point (Pt. 86.4m) notation as an appropriate name for it either from historic research or local enquiry has not been found, 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 the coast to its north-east, the A5025 road to its south-west and a minor road to its south-east, and has the village of Moelfre towards the east south-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 included in the Hills to be surveyed sub list, and included as a twin topped hill with the prioritised summit given at SH 484 876 with an accompanying note stating; Two tops of same height – other at SH 482 874. 

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 29m of drop, based on the twin 86m summit spot heights that appear on the Ordnance Survey 1:25,000 Explorer map and the 57m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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. 

LIDAR summit image of Pt. 86.4m (SH 482 875)

The summit height produced by LIDAR analysis for these two tops is 86.379m positioned at SH 48231 87520 and 86.169m positioned at SH 48453 87717.  As LIDAR has split these twin map heighted tops and as the higher was the previously listed non-priority top this comes within the parameters of the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies when the hill’s high point is found to be positioned; in a different field, within a different map contour, to a different feature such as in a conifer plantation, to a different point where a number of potential summit positions are within close proximity, a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct. 

Therefore, the summit height produced by LIDAR analysis is 86.4m and this is positioned at SH 48231 87520, this position is given an 86m spot height on contemporary Ordnance Survey 1:25,000 Explorer maps, and is approximately 240 metres south-westward from where the previously listed priority summit is positioned. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Pt. 86.4m 

OS 1:50,000 map:  114

Summit Height:  86.4m (LIDAR) 

Summit Grid Reference (New Position):  SH 48231 87520 (LIDAR)               

Bwlch Height:  57.0m (LIDAR) 

Bwlch Grid Reference:  SH 47995 86997 (LIDAR) 

Drop:  29.4m (LIDAR) 

 

Myrddyn Phillips (September 2021)