Mapping Mountains – Summit Relocations – Y Trichant

Foel Gron (SH 583 621)

There has been a Summit Relocation to a hill that is listed in the Y Trichant, and which was initiated by LIDAR analysis and confirmed by a survey with the Trimble GeoXH 6000, both of which were conducted by Myrddyn Phillips, with the latter taking place on the 06 & 10.10.18.

Foel Gron (SH 583 621)

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

Y Trichant – Welsh hills at or above 300m and below 400m in height with 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Foel Gron and it is adjoined to the Glyderau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by minor roads with the A4244 road to the north-west and the A4086 road and Llyn Padarn to the south-west, and has the villages of Deiniolen towards the north and Llanberis towards the south.

LIDAR image of Foel Gron

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 353m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map which is positioned at SH 58390 62231 on the eastern side of a stone wall that crosses the upper part of this hill.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website with the cursor indicating the position of the relocated summit

Three positions on the summit area of this hill were surveyed with the Trimble GeoXH 6000, resulting in:

1^st position: 351.577 at SH 58388 62224

2^nd position:  351.482m at SH 58403 62175

3^rd position:  351.585m at SH 58359 62170

The Trimble GeoXH 6000 gave the third position as the higher, and this corresponds with LIDAR analysis.

LIDAR summit image of Foel Gron

The summit height produced by the Trimble GeoXH 6000 is 351.6m and is positioned at SH 58359 62170 and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or 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 the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

The summit height produced by the Trimble GeoXH 6000 survey is 351.6m and is positioned at SH 58359 62170, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 65 metres south south-westward from where the 353m spot height appears on the Ordnance Survey 1:25,000 Explorer map.  

Gathering data with the Trimble GeoXH 6000 at the summit of Foel Gron (on right) with the old position of the summit on the left

The full details for the hill are:

Group:  Glyderau

Name:  Foel Gron

OS 1:50,000 map:  114, 115

Summit Height:  351.6m (converted OSGM15)

Summit Grid Reference (new position):  SH 58359 62170

Bwlch Height:  319.3m (LIDAR)

Bwlch Grid Reference:  SH 58675 62194 (LIDAR)

  

Drop:  32.3m (Trimble summit and LIDAR bwlch)

For details on the survey that relocated the summit position of this hill

Myrddyn Phillips (March 2019)