Sunday, 14 August 2016

Mapping Mountains – Trimble Surveys – Y Cymoedd

23.07.16  Mynydd Ton (SS 947 939, position Trimbled)    

Mynydd Ton (SS 949 940)

I’d visited Mynydd Ton once before in February 2003 when I followed the track leaving the A 4061 toward a forest break that gave relatively easy access toward where the 535m map heighted trig pillar was situated.  On that day I found ground about a minute away from the trig to be slightly higher, happy with my efforts I retraced my inward route back to my car.  Since my visit a number of Ordnance Survey maps have become available online, including the series of old Six-Inch maps and I believe it was Mick Moore who found a 1,769ft (539m) height on one of these maps that is adjoined to an ancient cairn which is approximately 175 metres south-west from where the trig pillar is positioned.  Therefore I wanted to re-visit the hill and the relatively newly discovered map high point.

As I left my car in a large lay-by near to the high point of the A 4061 the sun was out and young children were happily waiting next to an ice cream van as sheep also queued for any odd piece of food thrown their way.

The view north-east from the lay-by

A track leaves this road and heads up toward the forested summit area of Mynydd Ton, as I walked toward it two trail bikes were going through the gate and sped off across the hill’s northern flank, ahead was a car chugging its way up the track.  As I gained height there were other cars parked high on the track with a number of people flying model aircraft, I said my ‘hello’s’ and continued on the track to where it enters the forestry, I then turned right (southward) and followed a path beside the large conifer plantation to where a wide forest break gives access toward the map high point of the hill. 

Seemingly abandoned in the forest break was a four by four vehicle with its front windscreen partly smashed and its front end also badly damaged, I took a few photographs of it and continued down the forest break wanting to see if I could find the trig pillar that I’d previously visited, deciding that I’d had enough tree bashing for the day from my recent visit to Mynydd Ystradffernol, I back-tracked and headed in to another small forest break where the ancient cairn is situated and where the 1,769ft (539m) Six-Inch map heighted summit is positioned.

The abandoned four by four in the forest break

The cairn has been re-modelled and sits atop an ancient mound, past exploration found a central cist although this seems no longer in evidence.  I positioned the Trimble atop my rucksack deciding that the ground immediately beside the base of the cairn was slightly higher than the solid ground in the centre of it, and left it slowly ebbing down to its 0.1m accuracy level before data should be logged.  During this process I stood beside the trees and waited patiently, looking out past the re-modelled cairn and ancient mound to bright sunshine and the opposing conifers as they stared back at me.  I checked the equipment’s downward progress and once the accuracy level was attained I pressed ‘Log’ and retreated to the periphery of the trees and waited for five minutes of data to be collected.

Gathering data beside the ancient cairn on Mynydd Ton

The Trimble set-up position beside the ancient cairn on Mynydd Ton

As I packed the Trimble away I looked back at the mound and cairn and wondered if I would ever re-visit.  I then headed down the hill and visited the connecting bwlch which was just above where I had parked my car.  I’d examined this area via a Google car the previous evening and knew that a stone wall positioned on the south-eastward side of the road would give the Trimble elevation above its immediate surrounds.

Once at the top of the road which constitutes the area of the bwlch I judged the ground at the base of the wall to be the point of the critical bwlch and measured a 1.23m offset between the Trimble’s internal antenna and the ground at its base and set it to gather another five minute data set.  When it had collected its all-important data I walked the few metres down the road to my car and drove a kilometre westward toward my last hill of the day.

Gathering data at the critical bwlch of Mynydd Ton

Survey Result:

Mynydd Ton

Summit Grid Reference:  SS 94791 93954 (based on Trimble survey with the summit now relocated to SS 94931 94058)

Bwlch Height:  443.1m (converted to OSGM15)

Bwlch Grid Reference:  SS 93953 94456

Drop:  91.1m (based on Trimble survey, 92m based on summit relocation and Subhump status confirmed)

Dominance:  17.20%

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