Sunday, 31 July 2016

Mapping Mountains – Significant Height Revisions – Y Trichant

Penmaen Mawr (SH 704 752)

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 that was conducted on the 14th July 2016 to a hill that is listed in the Y Trichantwith the hill subsequently analysed with LIDAR data by Aled Williams and it is the latter result that is being detailed in this Significant Height Revisions post.

The criteria for the listing that this height revision affects are:

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.  Sub-Trichant - Welsh hills at and above 300m and below 400m in height that have 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming has been published on Mapping Mountains.

The hill is named Penmaen Mawr  and it is situated in the Carneddau range of hills, and 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 summit is a part of the hill named Penmaen Mawr and the extended hill has been quarried with its old 1,550ft (472m) map heighted summit now a distant memory as the whole inner section of the summit has been blown apart leaving two remaining tops with this post concentrating on the lower easterly summit.

The lower easterly summit is impressive as it forms a sheer rock face from its south and has steep slopes descending northward to the A 55 below.  Each summit is listed by the same name of Penmaen Mawr as they are both a part of the hill that is known by this name.

The summit area for the whole of Penmaen Mawr now appears on Ordnance Survey maps as a blank area with ‘Quarries’ written over it, and therefore is devoid of any uppermost continuous contour rings, which is the norm for the representation of quarried areas on Ordnance Survey maps, with the highest contour line being 350m for the area where the lower easterly peak is situated.

Therefore this hill’s new summit height is 385.8m (LIDAR data) which is 35.8m higher than its uppermost contour line on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and its 31.3m drop value is sufficient for it to be classified as a Trichant.

The full details for the hill are:

Cardinal Hill:  Tal y Fan

Summit Height:  385.8m (LIDAR data)

Name:  Penmaen Mawr

OS 1:50,000 map:  115

Summit Grid Reference:  SH 70441 75241

Drop:  31.3m (LIDAR data)

Aled with Penmaen Mawr (SH 704 752) in the background

Myrddyn Phillips (July 2016)

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