Wednesday, 27 July 2016

Mapping Mountains – Significant Height Revisions – Y Pedwarau


Penmaen Mawr (SH 698 755)

This is the thirtieth post under the heading of Significant Height Revisions, and the Trimble survey that resulted in this height revision was conducted on the 14th July 2016 in good, clear conditions.

The thirtieth major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the northern Carneddau in the company of Aled Williams who had suggested the walk.

The hill is positioned above and to the immediate south of the busy A 55 as it heads westward between the towns of Penmaenmawr and Llanfairfechan, which are situated to the hill’s east and west respectively.

The hill is named Penmaen Mawr and its summit area has been quarried.  Before the first quarry opened in 1830 and the subsequent resulting expansion of operations the hill was substantially higher, with a 1,550ft (472m) map height given it on the Ordnance Survey Popular and New Popular One-Inch maps, with this height also appearing on the Ordnance Survey Six-Inch map published in 1888.

The quarrying of this hill has created two summits with a gaping hole between, the westerly summit is higher than the easterly, although the latter is more impressive due to a shear rock face leading up to its high point.  Both tops were Trimbled with the following results:


Penmaen Mawr:  390.4m (converted to OSGM15) at SH 69865 75523

Pt. 384.9m, Penmaen Mawr:  384.9m (converted to OSGM15) at SH 70200 75727


Over recent years the summit area of this hill has appeared without any uppermost contours as is the norm for quarried ground on Ordnance Survey maps, with the highest contour being 370m which appears on the upper western part of the hill.

Therefore this hill’s new summit height is 390.4m (converted to OSGM15) which is 20.4m higher than its uppermost contour on current Ordnance Survey maps.


The full details for the hill are:

Cardinal Hill:  Carnedd Llywelyn

Summit Height:  390.4m (converted to OSGM15)

Name:  Penmaen Mawr

OS 1:50,000 map:  115

Summit Grid Reference:  SH 69865 75523

Drop:  26.9m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data 0.39m above the summit of Penmaen Mawr (SH 698 755) which resulted in this hill's significant height revision



Myrddyn Phillips and Aled Williams (July 2016)






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