Friday, 3 June 2016

Mapping Mountains – Significant Height Revisions – Y Pellennig, 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales

Emsger (SM 651 226)

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig30-99m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on the 14th May 2016 in good, bright conditions, perched beside a lighthouse on one of the most remote places in the whole of Wales.

The criteria for the three listings that this height revision affects are:

Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams.

30-99m Twmpau - These are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward, and the list is authored by Myrddyn Phillips. 

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  The list is authored by Myrddyn Phillips.

The hill is positioned on the island known as Emsger, which is also commonly known as South Bishop.  This island is positioned an approximate 8km (5 miles) west of St David’s Head in western Pembrokeshire, and unless being a competent and enthusiastic seal, it can only be approached by boat.  The island forms a part of the Bishops and Clerks chain of islands which form a compact groups of islets; all are rocky and are aligned northward to southward with North Bishop, Carreg Rhoson, Daufraich and Emsger being the main named island in each small group. 

The island is predominantly rock and if not for a series of steps leading up toward its summit its ascent would no doubt prove more problematic.  The upper part of Emsger has a lighthouse on it; this was built in 1839, and was converted to operating by electric in 1959, and demanned and automated in 1983.

The upper part of the island now has the lighthouse and associated buildings and platforms built on it, and therefore what once constituted the natural summit of the island is either buried under the lighthouse / platforms or it was destroyed during construction of the lighthouse.

I visited Emsger with Adrian Rayner, Ayako, Rob Woodall, Jon Glew, Sheila Glew, Sarah Kerr and Bob Kerr, and a quick assessment of what is left of natural ground pinpointed that this is situated just to the south-west of the main southerly corner of the lighthouse and its grounds.  This position was adjacent to steps leading down to the island’s helipad.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 37m summit height, which originates from the spot height on the Ordnance Survey 1:25,000 Explorer map, with the spot of this spot height positioned on the south-east part of the land immediately adjacent to the lighthouse.  This is on a part of the construction and is man-made; however natural ground exists close to this point but it is significantly lower.

Therefore this island’s new summit height is 33.8m (converted to OSGM15) which is 3.2m lower than its previously listed height of 37m which appears on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Island:  Bishops and Clerks

Summit Height:  33.8m (converted to OSGM15)

Name:  Emsger

OS 1:50,000 map:  157

Summit Grid Reference:  SM 65116 22619

Drop:  33.8m (converted to OSGM15)

Dominance:  100.00%

The Trimble GeoXH 6000 gathering data 0.99m above the highest remaining natural ground at the summit of Emsger, otherwise known as South Bishop (SM 651 226) which resulted in this island's significant height revision

Myrddyn Phillips and Aled Williams (June 2016)

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