Mapping Mountains – Trimble Surveys – Carnedd Llywelyn

14.07.16  Penmaen Mawr (SH 698 755), Penmaen Mawr (SH 702 756), Clip yr Orsedd (SH 711 747) and Moelfre (SH 717 744)

Penmaen Mawr (SH 698 755)

When seen from the A 55 the northern aspect of Penmaen Mawr rises in scree laden slopes to what was once a proud and prominent hill.  This hill has now been quarried and where a 1,550ft (472m) map heighted summit once was, there is now a gaping hole.  Quarrying this hill also destroyed an ancient hill fort that encircled the summit.  In its time Penmaen Mawr would have been an impressive hill as along with its ancient hill fort it was prominent above its surrounding lands as the bwlch that connected this hill to its adjacent neighbour of Clip yr Orsedd is, according to current maps, between 360m – 370m in height, giving the old hill over 100m of prominence.

Destroying the hill has meant that Penmaen Mawr can no longer be considered for Hump (HUndred Metre Prominence) status, and that its Pedwar (Welsh 400m hills) status has long gone with the last stick of dynamite used to blow the summit area to bits.  However, no accurate summit height is known for what remains of the hill and it had long been a priority to survey.

I met Aled at 5.00pm in Dwygyfylchi where we left his van and continued in my car to our parking spot high on a minor road above Llanfairfechan.  It was only a short walk up a track to the bwlch connecting Penmaen Mawr with Clip yr Orsedd, and when we arrived it was relatively easy to pinpoint its critical position.

As the Trimble gathered five minutes of data we chatted with a man who was out for an evening walk, and once the data set was complete I packed the equipment away and started up the gravelled slopes of quarried debris toward the first high point of what remains of the hill.

Gathering data at the critical bwlch of the two Penmaen Mawr summits

This first high point was no more than a mound of quarry debris and we had both spotted it when driving on the A 55 earlier in the day as it rises steeply and is pronounced.  Remarkably it was relatively stable when we climbed up it.  As the Trimble gathered data I stood immediately below it whilst Aled wandered over to look down into the gaping hole of the quarry.  Dotted about where remains of ancient and relatively modern habitation with the lower rock walls of ancient round huts still to be found, whilst the old quarry had its own more modern buildings, many now dilapidated and left to nature’s way.

Aled with the lower of the two Penmaen Mawr summits in the background

Over recent days Aled had scrutinised this hill via photographs and maps and realised that the easterly point of what remains of the hill may have sufficient prominence to be classified as a Sub or even a P30, and therefore after making our way over to the remaining natural high point and Trimbling it we headed down to the connecting land between the westerly and easterly high points, this proved to be on a steep mound of gravel beside long grasses and nettles, it too was also Trimbled.

Gathering data from the higher of the two Pernmaen Mawr summits

Heading toward the bwlch connecting the summit of Penmaen Mawr with the lower easterly summit

What remains of the hill on what is now its easterly high point is impressive as the quarry has gauged the upper hill into a cliff which gave us a little hands on rock excitement, once on its ridge the view down the coast toward Gogarth and Llandudno sprang into view.  The ridge was fun and gave us a small scramble of sorts with the drop to our right increasing as height was gained.

The southern face of the lower of the two Penmaen Mawr summits consists of an impressive looking rock face

Since the survey with the Trimble GeoXH 6000 Aled has analysed LIDAR data and the high point of the hill is not where data was gathered from and therefore the details given later in this post are those taken from LIDAR data.  When we reached what we thought to be the high point I set the Trimble on a large rock which was immediately above a gaping drop, not wanting to lose the Trimble to an early death I set it up on its dog lead, aligned its internal antenna with the highest part of the rock and sat below it with the lead fixed to the Trimble and securely around my wrist for the five minutes of data collected.

Heading toward the lower of the two Penmaern Mawr hills

Gathering data on the lower of the two Penmaen Mawr hills

The view east toward the shapely Foel Lus

As we headed down to the track where the first data set for the bwlch for Penmaen Mawr had been gathered, there was also an alternate connecting bwlch for the easterly high point to survey, this we thought to be on a track and connected the easterly high point to the higher Penmaen Mawr.

Gathering data at the area of the bwlch of the lower of the two Penmaen Mawr summits

However, the surveying of Penmaen Mawr had not ended as there was also an alternate bwlch position to survey for the high point of the hill, and this was on the way up towards our next hill; Clip yr Orsedd.  Once five minutes of data were gathered from this point we walked up to the summit of Clip yr Orsedd as the sun disappeared into a milky sky.

Our original plan was to do a two car walk and continue as far as Foel Lus, a 362m map heighted hill at SH 732 761, but we’d already conducted eight surveys and been on the hill for three hours, and if we continued toward Foel Lus in all likelihood we’d be descending a steep hill in darkness, therefore we quickly revised our plan and decided to continue to Moelfre and descend the green track on the southern side of Clip yr Orsedd straight back to my awaiting car.

Gathering data at the summit of Clip yr Orsedd

By now an evening’s chill had set in and the slow ebb of dusk was gathering.  Beyond the summit of Clip yr Orsedd we joined a path heading down toward its connecting bwlch with Moelfre, we assessed the lay of land and decided that the critical point was beside the track which crosses a reed invested bog, once five minutes of data were gathered we wandered up the steep northern slopes of Moelfre.

This hill has two potential positions for its critical bwlch and time dictated that only one could be surveyed, so after a five minute data set was collected at the summit I set the Trimble up at the neatest bwlch position and Aled wandered off in the direction of Tal y Fan to inspect the other bwlch option.  The bwlch nearest to Tal y Fan looked decidedly lower, and although a visual inspection is not ideal as the human eye can have difficulty judging hill heights, it did at least give us inkling which was lower and therefore the position of the critical bwlch of Moelfre.

Gathering data at the summit of Moelfre

As the Trimble gathered the last of its 300 data points, Aled re-appeared and said that the bwlch nearest to Tal y Fan looked at least 3m lower than where the Trimble was now gathering data, this was important as this hill is currently listed as a Sub-Pedwar with a drop of c 21m, so the position and height of its critical bwlch is all important.

After packing the Trimble away we walked down to the green track and followed it in dimming light arriving back at my car at 9.50pm.

LIDAR image of Clip yr Orsedd (SH 711 747)

LIDAR – Postscript 

Since visiting these hills full LIDAR coverage is now available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height and positional data that is now freely available for England and Wales.  Consequently the numerical details for these hills have been analysed using this technique, resulting in the LIDAR height and position being prioritised for some of these hills.

Survey Result:

Penmaen Mawr

Summit Height:  390.4m (converted to OSGM15) (significant height revision and 390m Double Sub-Pedwar addition confirmed)

Summit Grid Reference:  SH 69865 75523

Bwlch Height:  363.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 70332 75118

Drop:  26.9m (390m Double Sub-Pedwar addition confirmed and Sub-Trichant addition confirmed)

Dominance:  6.90% 

 

Penmaen Mawr

Summit Height:  385.8m (LIDAR) (significant height revision)

Summit Grid Reference:  SH 70292 75649 (LIDAR)

Bwlch Height:  354.5m (LIDAR)

Bwlch Grid Reference:  SH 70441 75241 (LIDAR)

Drop:  31.3m (LIDAR) (Trichant addition)

Dominance:  8.11% (LIDAR)

  

Clip yr Orsedd

Summit Height:  426.6m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 71185 74743 (Trimble GeoXH 6000)

Bwlch Height:  387.5m (LIDAR)

Bwlch Grid Reference:  SH 71805 74672 (LIDAR)

Drop:  39.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  9.19% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Moelfre

Summit Height:  433.0m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 71733 74418 (Trimble GeoXH 6000)

Bwlch Height:  414.7m (LIDAR)

Bwlch Grid Reference:  SH 72254 74153 (LIDAR)

Drop:  18.3 (Trimble GeoXH 6000 summit and LIDAR bwlch) (400m Sub-Pedwar deletion) 

Dominance:  4.23% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet.