Mapping Mountains – Trimble Surveys – Cymoedd Gwent

12.08.15  Mynydd Llangynidr (SO 123 151) and Blaen Onneu (SO 147 159)  

Blaen Onneu (SO 147 159)

Mynydd Llangynidr and Blaen Onneu are situated between two mountainous roads, the one to the east is the B4560 and goes from Llangynidr in the north to Garnlydan in the south, whilst the road to the west heads toward the Trefil Qarries and ends in a rough track.  The land between these two roads where the hills are situated is unenclosed and gives a great sense of openness with extended landscapes and tranquillity predominating.  The land is also rather wild and if not for the path between the hills it would be a rough traverse from one summit to the other.

We parked toward the top of the Trefil road where there was still a semblance of tarmac, this road is marked in yellow on current Ordnance Survey maps which indicates that it is public, but unbeknownst to us the road is closed between the hours of 5.00pm – 6.30am when a barrier is brought down over it and locked.  Unfortunately when we ended our walk we were locked in, but more of that later.

Our first objective was the critical bwlch of Mynydd Llangynidr which is listed as a 500m Twmpau as well as a Hump with c 102m of drop.  As the summit of this hill is crowned by a large ancient cairn there is a possibility that its 557m summit spot height is taken to the top of the cairn and not to the natural ground at its base.  If this was so the hill may lose an all-important 2-3 metres from its map height when accurately surveyed.

The lay of land at the bwlch was not overly difficult to judge and soon the Trimble was placed on my rucksack and gathering data with a 0.43m offset measured to take off after the data were processed.

Gathering data at the critical bwlch of Mynydd Llangynidr

The route toward the summit seemed pathless from this approach but never proved difficult as when height was gained we came across sheep tracks criss-crossing the open land with many heading up toward our next objective.  I looked back occasionally whilst on the ascent and the thin ribbon of road looked almost river like with the high mountains of Pen y Fan and the Beacons forming a backdrop.

Mark on the ascent of Mynydd Llangynidr

As we popped over the penultimate moorland ridge the large summit cairn came into view, its name is appropriately Garn Fawr, and it is Bronze Age and approximately 20 metres in diameter.  Its inner structure has now been fashioned as a wind shelter with one or two others joined at its side, but the majority of the base of the cairn seems undisturbed.  This ancient cairn along with many of its counterparts positioned on similar hill tops would have been for burial.

Approaching the cairn I picked out land at its base that looked the highest, and then proceeded to walk around its base, after inspecting the base of the cairn from a lower position the land that I had judged to be the highest, remained so.  Again the Trimble was positioned on the top of my rucksack for it to gain elevation, a measurement offset of 0.43m was recorded and it quickly attained the 0.1m accuracy before data can be logged.  Once it was gathering data I fancied a butty, banana and a drink, and felt rather abject when I realised they were still in my rucksack – ho hum!

Gathering data from the highest bit of land at the base of the large ancient cairn at the summit of Mynydd Llangynidr

Looking down from the top of the ancient cairn to the Trimble set-up position

As the last of the 300 points of data were collected I approached the equipment, switched it off, packed it away, grabbed my rucksack and its all-important contents and sat down for drink and food.

As we sat and ate we discussed the complexities of the cairn and its importance in the height of this hill and its possible dethroning from Hump status.  I gave the margin of uncertainty for height placement for the set-up position of the Trimble as 0.3m, this is relative to the ground at the base of the cairn and not for higher ground that could be under the cairn, this is impossible to judge so I did not try to do so.  We also wondered about the height of the cairn and our best estimate was between 3m - 5m.

Between us and the summit of Blaen Onneu is the Chartist Cave and that’s where we headed to next.  I’d only visited each of these summits once before as single bags from their nearest roads, but had a longing to visit this cave for a number of years.

The Chartist Cave takes its name from the 1839 Chartist uprising and it was used to stockpile weapons for the upcoming march by Chartist rebels on Newport in November of that year.  It is also recorded by older Welsh names of Ogof Fawr (big cave) and Tylles Fawr (great hole).  The cave entrance has a broad arch formed of Twrch Sandstone, commonly known as Millstone Grit, which overlays the Limestone beneath.

Approaching the entrance to the Chartist Cave

A good path leads from the top of Mynydd Llangynidr and its ancient Garn Fawr all the way to the caves entrance where a plaque commemorates the uprising.  As explained on the plaque the Chartist uprising led to the greatest armed clash between government forces and British people in the nineteenth century, and resulted in over 20 deaths and the last mass treason trial undertaken in Britain.

The plaque on the side of the cave

It still amazes me that authority can dictate against the will of the people and justified wants are battled against to the point of death and accusation of treason.  It seems that some powers that be seldom constitute justifiable change unless given an almighty great shove to do so.

From inside looking out

We examined the cave and its depths where at least two further smaller chambers disappear into darkness, a lovely place to visit and to combine it on the same day as a visit to the Aneurin Bevan Memorial Stones seemed rather apt.

The continuation of one of the small chambers

The path beside the cave continued all the way to the summit of Blaen Onneu, on the way we passed a group of teenagers on their Duke of Edinburgh award scheme outing, where overladen rucksacks and a seeming willingness not to know in which direction to go is the order of the day.

Thankfully a path exists between the two summits, otherwise it would be rough going

On the way to this summit we looked out toward where the hill’s bwlch lay, as it’s currently listed with c 27m of drop in the 500m Sub-Twmpau and with 28m of drop in a Sub-Dewey list it has an outside possibility of reaching the echelons of P30 status.

The summit of Blaen Onneu is situated about three metres from the base of its trig pillar and as the Trimble gathered its five minutes of data I replenished my energy levels with sustenance and took a few photographs as the late afternoon light started to enhance the land.

Gathering data at the summit of Blaen Onneu

All that now remained was an examination of this hill’s bwlch and a long walk back on the path past the Chartist Cave and Garn Fawr to the awaiting car.  We strode off with two ten figure grid references already input into Mark’s hand-help GPS for where I had estimated this hill’s critical bwlch to lie.  The first of these was off the main path in an area of long grass with occasional patches of heather giving colour to the predominant greens.  Whilst Mark stood at the point of the first ten figure grid reference I stood on lower ground between him and the summit on the hill to hill traverse, between the two of us was an intervening bump and away to our south looked to be much higher ground on the valley to valley traverse.  This whole area was proving complicated to judge and there was a simple reason for it; sink holes, these form as the land collapses into the Limestone beneath and when this occurs in the area of a bwlch it instantly gives two possible positions on the valley to valley traverse for where the critical bwlch may be positioned.  What we faced was a land consisting of one large sink hole with another to our north and as we really got to grips with judging and surveying the land there were another two to our south.

We had to get surveying as our original plan was to do another walk after this one and that possibility was quickly receding.  I joined Mark and set the Trimble up and waited until the o.1m accuracy appeared on its screen and then pressed ‘Log’, as the Trimble gathered data Mark examined the land where I had previously been standing, which by eye was definitely lower than where the Trimble was now set up.  However, once five minutes of data were gathered Mark was striding off toward where the second ten figure grid reference was directing him to go and telling me not to survey the point where I had originally stood just yet, as the lay of land was much more complicated that I had first judged.

The first of three points surveyed for the critical bwlch of Blaen Onneu

The second point that I had estimated for the position of the critical bwlch of Blaen Onneu lay to the south in a morass of green tussock grass that stretched for an age, all uniform and delightfully wild.  The margin of uncertainty for height placement would be large in such a place and I grabbed a figure out from the wilderness and scribbled 0.8m down in my note book as the Trimble started to collect its data.

The second of three points surveyed for the critical bwlch of Blaen Onneu

Back to our north I kept looking toward the ground where I had first stood and knew that this also needed to be Trimbled, so when the equipment was packed away we headed back and Mark then pointed out yet another sink hole between the point where I had first stood and the land further north, by now time was of the essence as we had a two hour drive to get back to Welshpool and Mark a further hour’s drive to Mold, our hopes of another walk after this one were now just about shelved.

Heading back out of the great expanse of grassland toward where the third bwlch survey took place, which is conveniently placed directly above Mark's head in this photograph

As Mark patiently waited in the evening sunshine I took a third bwlch data set and as the Trimble gathered data I looked at the land beyond the sink hole to the north and visually judged this to be lower and therefore as it was on the valley to valley traverse it did not need surveying.

The third and last point surveyed for the critical bwlch of Blaen Onneu

Happy with what we had done we set off back on the path toward the cave and the large cairn, this time we kept to the path as it bi-passed the summit of Mynydd Llangynidr to its south and continued on its downward route to the rough paved road below.

By the time we reached the car it was 7.20pm and the distance we had to travel back home dictated that there would not be another walk today.  All that remained was to get boots off, change and drive back home, or so we thought.

As I got changed a large quad bike roared down the gravelled road and I flagged the driver down thinking he may be a local farmer who I could ask about locally known names for the hills, the driver was Greg Owen from Rhymney and he asked us if we planned on driving down the road and said that if we did, we couldn’t, as the barrier was now locked.  We didn’t even realise that a barrier existed, Greg proved a great help as within a few minutes I was on the back of his quad bike and we were roaring up the track to the top quarry just under the summit of the hill that many list as Cefn yr Ystrad to ask the security guard for the key to unlock the barrier. 

Greg Owen - a saviour in time of need

The security guard didn’t have the key and directed us to the bottom quarry where another security guard would be able to help us.  We roared back down the hill to the car where Mark was patiently waiting, soon we were following Greg as he led the way on his bike and indicated where we should go toward the lower quarry.  Greg had been a great help and without him we may have ended up sleeping in the car until the early hours when the barrier was unlocked.

I parked the car next to a locked gate at the lower quarry, which was still high on the slopes of Mynydd Llangynidr and went in search of the security guard, it took me a few minutes to find him, but when I did he was very helpful, and as he couldn’t drive he came down in the car with Mark and I to unlock the barrier, only for him to then walk back up the hill to man his post, we offered a small payment for his help which he politely declined. 

It had been another good day on the hill with one or two interesting survey results to look forward to, with the ending to the last of our walks resulting in the kindness of two local people to get us out of our predicament.

For those heading up the Trefil road the barrier is locked at 5.00pm and unlocked at 6.30am.  There are on-line write ups stating that the barrier remains locked at weekends. 

  

 

Survey Result:

Mynydd Llangynidr

Summit Height:  557.6m (converted to OSGM15)

Summit Grid Reference:  SO 12343 15135

Bwlch Height:  455.2m (converted to OSGM15)

Bwlch Grid Reference:  SO 11034 15118

Drop:  102.4m (Hump status confirmed)

Dominance:  18.37%

Blaen Onneu

Summit Height:  541.0m (converted to OSGM15)

Summit Grid Reference:  SO 14700 15933

Bwlch Height:  515.6m (converted to OSGM15)

Bwlch Grid Reference:  SO 14039 15155

Drop:  25.4m (500m Sub-Twmpau status confirmed)

Dominance:  4.70%

For further details please consult the Trimble survey spreadsheet click {here}