Mapping Mountains – Trimble Surveys – Yr Wyddfa

07.07.26  Yr Wyddfa (SH 609 543, only bwlch surveyed)

The Trimble GeoXH 6000 and Leica Gs15 gathering data at the summit of Yr Wyddfa

In September 2014 along with Graham Jackson and John Barnard I surveyed the summit of Yr Wyddfa.  In attendance was Mark Greaves representing Ordnance Survey.  It was Mark who later processed the gathered data.  Our endeavours were filmed by Stephen Edwards of Cread Cyf and Aled Llŷr, with the film appearing on ITV Wales.

The summit architecture of Yr Wyddfa has changed over many years, with all manner of structures being built.  These have consisted of huts where horses were stabled and the Victorian tourists who ascended on them could rest, take in the view, if indeed one existed and recover from their exploits before the journey back down the mountain.

Over time huts evolved in to a hotel and latterly a summit café.  However, these constructions did not limit themselves to the ground surrounding the summit, they also took in the summit itself, with massive cairns of stone, a flag pole and latterly a summit plinth with a weather station and identification plague on top of what is fashioned to resemble a triangulation pillar.  This stands atop the aforementioned plinth which has been constructed over the natural summit tor.  Thankfully we have a bench mark height to the bedrock which can supposedly still be accessed from a small window on the side of the weather station.  It was the wisdom of Ordnance Survey who installed the bench mark and documented its height, as all we could do when resurveying the summit of Yr Wyddfa was take a measurement to the concrete plinth, which is an obvious man-made addition to the height of the mountain.

As with many listings, the qualification whether a hill should be included is dependent upon its drop.  This is the height difference between its summit and bwlch that connects to the next higher summit along its watershed.  The approximate position of the Yr Wyddfa bwlch had been known for many years and to my knowledge was first documented by Alan Dawson.  This connecting bwlch is positioned beside the Forth and Clyde canal in Scotland.

The Ordnance Survey give a 46m spot height on the 1:25,000 Explorer map at NS 76804 78578, which could be where the critical point of this bwlch is positioned.  However, map study shows two burns descending southward from the hillside above the small community of Kelvinhead.  As these two burns near the canal one heads westward and the other eastward, suggesting that the bwlch is positioned on ground between the two.  This is the best available evidence we have at the moment for the position of this bwlch, until LIDAR becomes available for this part of the country.

This was a survey I had wanted to do for many years, but opportunity was limited as I now rarely venture north in to Scotland.  However, with an offer to stay accompanied by John Kirk, in Mark Trengove and his wife’s newly built second home in Laide in Wester Ross, this gave us the prospect to survey this bwlch on our way north.

Arriving at Mark’s at midday we quickly packed my gear in his car and he then proceeded to drive to John’s in Burnley where we over-nighted before John took over the driving duties heading north.  As the hours of travel slowly ticked by the weather became more inclement with fine drizzled spots of rain hitting the windscreen.  By the time we left the M80 and drove in to Kelvinhead the sky was coloured light grey and light rain interspersed with more drizzle met us as I quickly got my walking boots on for the walk down to the canal. 

Heading down the path toward the bwlch

John seemed to know this area well and we followed him toward the gate giving access to the narrow path leading down beside what turned out to be one of the burns, which only showed its watery trickle as we approached the canal.  This burn was on our right as we descended, whilst the burn on our left was no more than a slight indentation consisting of lots of greenery, which as least intimated that water was in fact present. 

Nearing the bwlch

A gate gave further access to the canal towpath, and it was close to this gate where the majority of our efforts were concentrated, as all ground on the path descended to this point and beyond the gate all ground went uphill for a short distance to the canal towpath.  On our way through the gate we had a quick discussion where we considered the critical point to be positioned.  We then visited the canal which was unexpectedly wide at this point.  The surprise at its width was based on the experience of my local Montgomeryshire canal where two narrow boats crossing would be the limit; this canal was like a river.  However, John later explained that this part consisted of a water basin where boats could pass without difficulty. 

Arriving on the canal towpath

We stood beside the water for a number of minutes with John pointing out the ditch on the far side of the canal.  If whilst on the valley to valley traverse the height of a cutting was taken as the critical point of the bwlch, the ditch formed a major difficulty in our endeavours as from this vantage point it looked lower on the hill to hill traverse, but again John explained that breaking the ditch is a bank that goes in the hill to hill direction, thus increasing the high point of the valley to valley traverse if following the ditch.  Therefore, it seemed we were safe in taking the ground close to the gate as the critical point for the bwlch of Yr Wyddfa. 

The western view of the canal

Looking south on the hill to hill traverse with the ditch evident adjacent to the opposing bank

The eastern view of the canal

Once a few photos of the canal were taken we backtracked to the gate and had a good inspection of the path and its downward passage toward this point.  We initially considered gathering data from the ground immediately through and at the base of the gate, but soon the Trimble was moved to the path leading toward the gate.  Ground hereabouts within a ten metre distance looked consistently flattish and with little margin of uncertainly for such a survey the Trimble was quickly positioned on my rucksack, which in instances like this forms a convenient makeshift tripod.  Once the 0.1m accuracy level was attained before data should be logged, I pressed ‘Log’ and headed back through the gate to stand away from the equipment as it gathered its customary five minutes of data. 

The Trimble GeoXH 6000 gathering data at the bwlch of Yr Wyddfa

After data were gathered and stored I closed the equipment down and took a series of photos from various directions of the Trimble in situ.  It was then packed away and we headed up the path toward the dry confines of John’s car.  On the way we met David Henderson on his quad bike with three attendant sheep dogs scampering after him.  I flagged him down for a chat. 

The northern view from the bwlch

The eastern view from the bwlch

The southern view from the bwlch

The western view from the bwlch

We spent a number of minutes with David; he told us he’s known as Dov by all his friends.  I happily explained the significant of the land he farms and specifically the point on the path no more than five minutes down from where we were now standing.  He didn’t look amazed, which was a disappointment and seemed to take in the critical nature of this point in his stride.  Aw well! 

The view further east

David Henderson with Bessie, Roy and Peggy

Leaving the bwlch

After leaving David we continued on the slight uphill leading back to the houses in Kelvinhead.  By now the intermittent rain and drizzle had in the main relented, just long enough for me to get my walking boots off and after a quick repositioning of my gear around the back seat of John’s car, we were away on our trip heading farther north in to the beautiful wilds of northern Scotland. 

  

Survey Result:

Yr Wyddfa

Summit Height:  1084.8m (converted to OSGM15) (Ordnance Survey historical data to bedrock at summit) 

Summit Grid Reference:  SH 60985 54374 (Old triangulation pillar and Ordnance Survey historical data to bedrock at summit) 

Bwlch Height:  47.6m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  NS 75797 78295 (Trimble GeoXH 6000)

Drop:  1037.2m (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

Dominance:  95.61% (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

 

 

My thanks to Alan Dawson with help processing these data

 

For details on the 1^st summit survey of this hill

 

For details on the 2^nd summit survey of this hill

 

For further details please consult the Trimble Survey Spreadsheet 

Mapping Mountains – Trimble Surveys – Yr Wyddfa

02.09.14  Yr Wyddfa (SH 609 543)

Yr Wyddfa (SH 609 543)

Following the 5^th June reconnaissance of the summit of Yr Wyddfa we kept in communication with Stephen and Aled as we all organised for the day of the survey.  A number of organisations were contacted, including the Snowdonia National Park Authority who as part custodians of the mountain had an obvious interest in the result of its re-survey.  We also had a good contact at hand if needed, who was Dewi Davies; the Head Warden of the National Park who was one of the five people being filmed for ‘The Mountain’ programme.  Stephen was also in consultation with the Snowdon Mountain Railway and the manager of Hafod Eryri; the summit café, whilst we consulted with our contacts at Ordnance Survey.

Two things were evident from our reconnaissance; the first being that we would have to survey the summit either late in the evening or early in the morning, as the multitude of train passengers that visited the area of the summit during the day may hamper data collection.  The second being that the point where people walk up to and stand beside the triangulation pillar is on a man-made plinth, therefore should data be collected from this point or from the highest natural rock still visible on the periphery of the plinth.  We sought guidance from the Ordnance Survey.

The Ordnance Survey consulted their historical height records and informed us that the last known accurate survey of the mountain was in 1961.  The height given the flush bracket was then recorded as 1086.002m.  Although this flush bracket is retained on the current circular trig pillar its retention was an afterthought and it is placed 0.584m above the base of the trig.  In affect its current position has no accurate height meaning.

Prior to the construction of the 1961 trig pillar the Ordnance Survey had taken a measurement to a bolt positioned in the upper bedrock of the mountain.  It was this bolt that the 1961 trig pillar was positioned over, and it is this bolt that is now buried under the current 2009 construction of the summit plinth.  The Ordnance Survey instructed us to gather data from the base of the trig pillar which is the top of the summit plinth; we could then compare this measurement against the height of the bolt in the bedrock.

When assessing the summit plinth and remaining visible high points of natural rock on the reconnaissance we asked a number of people who had walked up the mountain where they thought the summit of Snowdon was.  The consensus of opinion was that it was ‘here, where I’m standing’, and that was the ground at the immediate base of the trig pillar at the top of the summit plinth.  This opinion is interesting as although the question was not a part of a scientific exercise it did at least summarise a layperson’s view on the matter.

Stephen soon gained permission for us to overnight in Hafod Eryri; the summit café and for us to go up the mountain on one of the last afternoon trains and come down the following morning on the goods train.  During our consultation with Ordnance Survey we asked if they would like to send a representative to be present during the survey, they said they would and it was quickly arranged that Mark Greaves, their Geodetic Analyst should be present.  Mark is one of the country’s leading authorities on GNSS technology and had represented the Ordnance Survey during two of our past surveys and one of our Press Conferences; these being Tryfan, Tal y Fan and Glyder Fawr respectively.

The date for the re-survey was set for Tuesday 2^nd September; all we hoped was that the weather was fairly decent.  When we met in the car park adjoined to the Snowdon Mountain Railway in Llanberis it was in glorious sunshine and with a high pressure system stabilised over the country the weather for the upcoming evening, night and following morning was going to be fine.

We were booked on the 4.30pm train, the penultimate one to make its way up the mountain on the day.  We carried all our gear on to the platform and stacked it neatly beside the ticket office.  We had enough gear for a grand tour of Europe, with all necessary surveying gear, a multitude of camera gear that Aled had brought, all our sleeping gear and mountain gear making up quite an impressive assortment.  We even took a ready-made meal waiting to be heated up in the summit cafe.

Our gear stacked up prior to transportation to the summit of Wales' highest mountain

The journey to the summit by train is rightly one of the most popular trips for anyone to undertake in north Wales.  It takes the train approximately one hour to make its way up the side of the Llanberis ridge to the summit of Yr Wydda, only breaking out on to the actual ridge near to Clogwyn Station, with dramatic views across the Llanberis Pass to the high Glyderau.

Aled filming as we pass Llechog

Once the train arrived at the summit platform we ferried all the gear out of our small compartment and assembled it on the platform before storing it in an out building.  A photo opportunity then presented itself, one which was not to be missed, dependent of course upon the final result.  Peering down from above was a neatly calved block of granite proclaiming the mountain’s height of 1085m. 

The granite facade of Hafod Eryri.  Would the height need updating?

As the last train down the mountain was not departing for another half an hour we relaxed in the café and were introduced to Jonathan Tyler; the manager of Hafod Eryri, Jonathan would be overnighting with us in the café and proved a very good and understanding host.

We were also introduced to Dewi Davies, the Head Warden for the Snowdonia National Park who had spent the majority of the day at or near to the summit filming with Bear Grylls, the famous adventurer.  Dewi explained that the filming with Bear had concentrated on the geology of the mountain.  When Dewi accompanied us outside as we walked toward the summit, he showed us fossils of small shells next to the stepped path leading up to the high point.  These were rather beautiful in design, and their position probably unknown by the vast majority of the estimated 400,000 people who visit the summit each year.

Before heading outside we were filmed with Dewi looking through a series of old photographs of the summit of Yr Wyddfa.  Some were from recent times when the old concrete café was still in situ; others were from the late 1800’s, early 1900’s when two buildings, described as Hotels were positioned beside a gigantic summit cairn.  All of these photographs helped us interpret what the area of the summit had looked like during the last 150 years or so.   

As the last train departed the summit of the mountain was now free of the multitude and we ventured out to visit the high point.  Most of our movements around the summit area were being filmed by Aled, who occasionally asked us to walk this way or that, and to repeat sequences until he was satisfied with the outcome. 

Considering how tranquil the late afternoon and early evening was it was amazing the summit had no one on it except for us, this helped tremendously as we could go about our work undisturbed. 

Since our reconnaissance we had considered a number of ways to survey the high point of Wales’ highest mountain and one of them was now tested.  Mark had brought a ‘plate’ that fitted in to the groves of the ‘spider’ at the top of the trig pillar.  This was put in place and our Leica GS15 was then attached to it, the data set from this point would give us an accurate position to the centre of the trig and an accurate height to the position of the equipment.  The offset between its position and the high point at the base of the trig pillar could then be ascertained by the use of a level and staff and subsequently taken off the processed result to obtain the final measurement. 

The pillar plate on top of the trig pillar

The Leica GS15 fixed on the pillar plate

However, as the plate and Leica GS15 was assembled Mark discovered that the hooks that are positioned on standard triangulation pillars were missing from this re-fashioned one.  We experimented with how stable the apparatus would be if we tied it down around protruding rocks on the side of the circular trig, we soon realised that this was not ideal and decided against using this method to re-survey the mountain.

We discussed our options and decided that as the wind speed was only 15-20mph that the equipment could be assembled on its two metre pole and left in place gathering data beside the trig pillar at the top of the summit plinth.  This would also enable any summit visitors to visit the trig and their heads to still be below the antenna, thus not disrupting any signals received by the antenna from orbiting satellites.

We then used the level and staff to take a series of readings around the summit plinth at the base of the trig, this gave us an average reading for its relative height and also pin pointed the high point of the plinth. 

Using the level and staff to determine the high point of the summit plinth

The Leica GS15 was soon in place on its two metre pole, we used a number of rocks on the lower part of the tripod’s legs to weigh it down just in case the wind speed increased.  Once happy with its position and stability the button was pressed and data started to be collected at 8.00pm.  During this time the sun sank ever downward and cast out magical colours across the land. 

Switching the Leica GS15 on for the three hour evening data set

As the evening was clear the warmth of the sun soon disappeared as it sank ever lower on the western horizon, and the wind speed added to the increasing chill.  Thankfully as evening turned to night the wind decreased in strength.

Evening turning to night as the sun sinks on the western horizon

When John, Graham, Mark and Stephen headed in to the café, I remained at the summit with Aled.  Both of us were happy enough looking out as the sun sank in to a layer of thin cloud balanced above the western horizon.  Aled filmed whilst I took photos, the red orb slowly cast out its last light and we were left in a world where all colour slowly drained from the landscape.  I’d wanted to experience the sun set from Yr Wyddfa for most of my adult life and it did not disappoint.

The sun setting over the trig pillar from the summit of Yr Wyddfa

As the last light ebbed from the evening sky Aled set his camera up to capture the scene.  I stood beside the trig pillar on the summit plinth and framed him silhouetted against a night of radiant darkened blue with the last slither of evening orange disappearing beyond the horizon.  Next to me the coloured leds of the Leica GS15 shone as data continued to be gathered.

Aled capturing the scene from just below the summit of Yr Wyddfa

At 9.30pm I ventured in to the café as there were rumours that Jonathan was cooking the world’s largest pasty.  Prior to this I had taken ten minutes of data with the Trimble from the top of the trig and had been joined in the darkness by Graham.

The Trimble GeoXH 6000 and the Leica GS15 both gathering data atop Yr Wyddfa

Gathering data from the top of the trig pillar atop Yr Wyddfa

When I entered the café it was ablaze with light and I quickly stripped my outer layer of clothing off, as the air conditioning made it similar to a tropical climate when compared to the night time vigil outside in the chill air on the summit.

When delivered the pasty was truly ginormous and required serious thought in how to tackle it!  We added cooked spicy bean burgers and small cakes made by Graham’s wife; Janet, to make the meal a sumptuous affair.  As we indulged ourselves the equipment remained on the summit collecting data, we had decided to leave it there unattended as no one had visited the summit for over three hours since we first emerged from the café at about 6.00pm.

Mmmmm yummy, a hugely ginormous pasty, this took serious consideration in how to eat the beastie

Earlier in the evening we had discussed with Mark what timeframe of data set was ideal for the Ordnance Survey, Mark advised us to collect data in two time frames, one in the evening and one the following morning, both of them the same length, we all decided that two data sets of three hours a piece was achievable.  And once the pasty had had its come-upance we ventured out and back to the summit, it was approaching 11.00pm and as we waited for the equipment to log its last data during the first three hour data set, Graham looked up to the heavens and pointed out the Milky Way as it cascaded across the sky.

We left the tripod and two metre pole in place overnight and retired to the comfort of the café, I slept in the shop which was a little surreal, but the word ‘slept’ may be a misnomer in this instance as any sleep was intermittent and by 4.15am I was up and about, quietly getting my gear ready for the morning’s data set.  Soon everyone else was up and sorting and packing gear.

By 5.15am the Leica GS15 had been put back on top of the two metre pole and by 5.20am the equipment was gathering data.  We now had another three hours of data to collect.  Some of us headed back inside the café whilst others remained outside watching the sky slowly become coloured in its morning awakening.

Looking toward Moel Siabod as we waited for the sun to rise

The previous evening’s attention had been westward toward the sea and the ever dimming colour as the sun set, this morning our attention was turned eastward toward Moel Siabod as the slither of orange hue above Capel Curig progressively expanded. 

The next hour was sublime as the sun cast beautiful colour around the eastern sky

The following two hours were sublime as darkness slowly evolved into dawn.  Pushing westward from the heartland of inner Wales was a bank of grey cloud, never lower than any summit, but nevertheless it slowly crept toward Moel Siabod, behind which the sky was turning its customary orange heralding the rising of the sun.

The Leica GS15 gathering its three hour early morning data set

When the sun appeared it was only for five minutes as it quickly disappeared behind the cloud bank, but although an initial disappointment this heralded a delicate show of colour as the land around Moel Siabaod was transformed into gentle and impressive colours with crimson hues merging into reds, scarlets and orange, all subtly changing as the early morning sky evolved in mood.

Sunrise from the top of Yr Wyddfa

Across Glaslyn the pointed peak of Crib Goch was framed against a darkened sky, but it was Moel Siabod that caught the eye as its bulk of shape lent itself to the forever changing light of morning.  The oranges and reds had gently evolved in to colours of rusty crimson’s.  Quite enchanted I stood and watched.

Crib Goch framed by delicate colour

s with all natural light shows there comes a time that the pinnacle of wonderment is replaced by an ebbing of colour, when this happened and the scarlet crimson’s diminished in intensity the eye was struck by the silver edged mist on Llynnau Mymbyr.

Llynnau Mymbyr emerging out of early morning mist

This had been somewhat neglected as the colour wash dominated, but the fragile gracefulness of mist now predominated as light cast out from behind cloud highlighted its flow from lake surface to lower hillside, all was accomplished in an elegant way as wisps of mist crept upward to be swallowed by the warmth of day.  It seemed as if the early morning awakening on the land of Eryri had been transformed into a Japanese silk painting, one of wonder and myth.

 

As the mist dissipated the dull ache of afterglow turned adjacent hillsides from radiant reds to blended blues and the world around Yr Wyddfa took on one of norm.

Radiant reds turned to blended blues

The equipment was switched off at 8.20pm and as we headed back inside the café we were happy in the knowledge that six hours of data had now been collected.  During the latter part of the morning’s data gathering Mark was busy processing the evening data set on his laptop, this gave us a provisional result of 1085.63m for the height of the summit plinth.  Soon afterwards we packed all our gear and waited for the journey down the mountain on the 9.00am goods train.

Mark processing the evening data set to obtain the provisional result

Once precise ephemeris data for the satellite positions had been published the two three hour data sets from the survey of Yr Wyddfa were combined into one which Mark Greaves later post-processed using Ordnance Survey state of the art Bernese software.  This gave an official height for the top of the summit plinth at the base of the triangulation pillar of 1085.67m, an increase of 4cm from the provisional result.

During this project we had studied a number of old photographs of the summit area dating from the late 1800’s to the early 2000’s, by doing so we distinguished comparable rocks and took height readings to these on our recce in early June.  From these measurements we estimated that the summit plinth had raised the height walkers reach when they stand beside the trig pillar by 0.8m when compared to the high point of the natural bedrock.  Our approximate 1084.87m height compares favourably with the 1084.74m height obtained during the 1961 survey.

The Ordnance Survey will adhere to the protocol of listing the height of Yr Wyddfa by the highest natural ground that is known and in this case, that is the rounded up figure of 1085m from the survey of 1961, therefore the current map height is unaltered.

However, for all those many thousands of people who visit this mountain of myth and legend; Yr Wyddfa / Snowdon the highest mountain in Wales, and who contemplate all those small steps ascending those 1085m to its top, well, the task just got a little bit harder as in affect they are ascending a 1085m high mountain and when that extra 1m of summit plinth at the top is gained they are peering down on land and sea that is 1086m below them!

Survey Result:

Yr Wyddfa

Summit Height:  1084.8m (converted to OSGM15) (Ordnance Survey historical data to bedrock at summit)

Summit Grid Reference:  SH 60985 54374 (Old Triangulation Pillar and Ordnance Survey historical data to bedrock at summit)

Bwlch Height:  47.6m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  NS 75797 78295 (Trimble GeoXH 6000)

Drop:  1037.2m (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

Dominance:  95.61% (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

Trimble GeoXH 6000 survey from 05.06.14: 1085.673m (converted to OSGM15)

Trimble GeoXH 6000 survey from 02.09.14: 1085.716m (converted to OSGM15)

Leica GS15 survey and processed with Ordnance Survey Bernese Software:

1085.716m (converted to OSGM15)

Ordnance Survey Result from 1961 Survey to High Point of Bedrock:

Natural High Point:  1084.74m (not converted to OSGM15) and 1084.786m (converted to OSGM15)

For details on the 1st summit survey of this hill

For details on the bwlch survey of this hill

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

Mapping Mountains – Trimble Surveys – Yr Wyddfa

05.06.14  Yr Wyddfa (SH 609 543) and Crib y Ddysgl (SH 610 551)

Yr Wyddfa (SH 609 543)

Yr Wyddfa stands as an iconic sentinel to a nation, the highest point in an ancient land, centred in Eryri where mountain and sea both meet.  It is bathed in myth and legend and holds the distinction of being the most visited summit in the British Isles with many hundreds of thousands of people either clambering up its ridges or arriving at its summit after being transported by train every year.

As befits such an iconic mountain its height is viewed as important.  After all without such knowledge part of this iconic status would not be given.  The mountain’s current given height is 1085m, this height and its imperial equivalent of 3560ft has been constant from the early part of the 1900’s. 

Earlier height documentation quotes 3570ft (1088m [Ordnance Survey One-Inch 'Old Series' 1st May 1840]), this height matches that given by the Rev William Bingley in 1801 who estimated the height from local sea level as 3570ft (1088m), saying that “It rises to a mere point, the summit not being more than 3 to 4 yards in diameter”.  Earlier still are two other height recordings, one by the renowned naturalist, traveller, writer and antiquarian; Thomas Pennant, who quoted an estimate of 3568ft (1087.5m), the other was by Mr Caswell from a survey in 1682 with instruments made by Flamstead who estimated the summit to be 3720ft (1134m).

The summit area of the mountain has withstood numerous man-made structures including hotels, huts, café’s, stone walls and a nearby railway terminus.  It is currently crowned by a summit plinth adorned with a circular triangulation pillar with a brass panoramic viewfinder on its top, there to distinguish the view for the many thousands who peer out in to the fog of mist when days aren’t especially clear.  When those days are clear and the view is savoured, one can be mesmerised by the light and shade as the play of light highlight mountain top, lake and valley, all at the foot of Yr Wyddfa as the great bulk of its eastern face plunges down toward Glaslyn and Llyn Llydaw, two timeless blue enhanced lakes.

We had wondered about the accurate height of Yr Wyddfa for a number of years, partly due to a flush bracket height quoted as 1086.002m in the OS Trig Database.  This height was taken to the top of a flush bracket that was on the side of the old triangulation pillar that once stood on the summit.  The year given for its completion and levelling is 1961.  As flush brackets are usually positioned 30 – 35cm above the base of the trig pillar, it would mean that the height to the base of the trig pillar would be approximately 1085.70m, and as heights are usually rounded up or down when they appear on the map, it seemed that this height was anomalous as it appears as 1085m on current maps.

There is also the unwanted dilemma of what constitutes the high point of the highest mountain in Wales; few would say it is the top of the trig pillar as this is man-made.  But if man-made objects should not count, isn’t the ground immediately below the base of the trig pillar also man-made?  Surely the high point of this most iconic of Welsh mountains should be taken to its natural high point and not something that man has built?  Advice on this specific subject would have to be sought from Ordnance Survey.

It was our intention to accurately re-height Yr Wyddfa with the latest GNSS technology and do our utmost in determining the remaining natural high point of the mountain.  During this process we would also gather height data for the ground immediately at the base of the triangulation pillar to satisfy those who enjoy such debates between ‘natural’ and ‘man-made’ summit structures.

The opportunity to re-survey Yr Wyddfa was prompted by Stephen Edwards who is the organiser of the Snowdon race and who operates CREAD Cyf, a company specialising in aspects of radio and TV coverage, centred on the outdoor world.  Stephen contacted us and we arranged a meeting with him to discuss the project.  Stephen had been present on some of our past surveys, including the ones that determined Glyder Fawr to be 1000.8m high (999m on then current maps) and Tryfan to be 917.5m high (915m on then current maps).  Since our last meeting he had teamed up with Aled Llŷr who runs Slam Media productions, which is an independent film company.

The project Stephen outlined was exciting as he knew of our intention to one day re-survey Yr Wyddfa, and he wanted this to be a part of a six programme TV series entitled ‘The Mountain’ which followed five people; Head Warden of the Snowdonia National Park, Hill Farmer, Train Driver on the Snowdon Mountain Railway, member of the Llanberis Mountain Rescue Team and the owner of the Halfway House café.  The series would follow these people and the seasonal impact the mountain has on their lives with Yr Wyddfa as backdrop but also intrinsic in their daily occupation.  Stephen envisaged that our re-survey of the mountain would form part of the programmes based around the summer months. Stephen suggested at least three visits were necessary, two to recce the summit area and the final one to measure the height and gather summit data.

The first recce was arranged for 5^th June 2014, we met Aled and Stephen in the car park adjacent to the Snowdon Mountain Railway and caught the 8.00am goods train to the summit along with the staff from the café and an entourage of cream cakes, various drinks and buttered scones, all neatly stacked for the hundreds of visitors due to disembark from the train over the course of the next nine hours.

Aled and John waiting to depart on the 8.00am goods train

This was a treat for us and one that we are very privileged to be offered, and thanks should be expressed to Stephen for arranging it and for the Snowdon Mountain Railway in letting us go to the summit in the train.  The major advantage with this was the ease of carriage for the weight involved, as a surveying team our equipment takes three people to carry it and Stephen and Aled also had their cameras and mountain gear.

The journey by train also fulfilled a life time’s ambition for Graham who had never previously travelled on the mountain railway, neither had John, I had; but have no memory of it as I was aged about eight or nine and went up with my parents and brother when on a family holiday in north Wales.

Part of the team assembled (L-R) Graham Jackson (Surveyor), John Barnard (Surveyor) and Aled Llŷr (Director)

The journey to the summit took about an hour, we left in the morning’s sunshine and when past the rocky peak of Llechog the mist enveloped us.  The remaining journey was done in the knowledge that it was going to be a wee bit chilly on the top, so much so that when we disembarked we instantly put on extra gear and headed straight in to the café for a hot cup of tea.  No sooner had the café doors been opened and one or two walkers came in.  Over the next couple of hours a whole multitude of people spilled out of the trains wearing all manner of exotic clothing.  We busied ourselves with conversation and timed our first sojourn out to the misty peak for when the train passengers had mostly departed.

Into the mist as we pass the peak of Llechog

Nearing the final ascent, Jonathan Tyler (Hafod Eryri manager) in red top and Stephen Edwards (Producer) on right of photo

Aled filmed us as we left the café and walked up the steps toward the summit, having visited the top more than 30 times I was pleasantly and somewhat relieved to find that what we had started to refer to as the summit plinth was not wholly man-made, as large embedded rocks make up the bottom few metres of summit structure.  These rocks are part of what is the summit tor and are the rocks that in 1801 the Rev William Bingley described as “It rises to a mere point, the summit not being more than 3 to 4 yards in diameter”.  It is surprising how little one notices when just visiting a summit for pure enjoyment, today we had a specific purpose and it was great to get to grips with the summit tor, examining the lower rock and seeing where the rock strata changed in position, this happens toward the top of the ‘mound’ and is continuous around it.  The lower section is made up of the ‘natural’ tor and has embedded rock usually slanting upwards, whilst the upper one metre – two metres has smaller rock arranged pointing inwards encircling the ‘mound’.  Further investigation proved these upper rocks to have been placed by man, as a number of them either moved when wriggled or came out when pulled; those that did were carefully replaced.  We then concentrated on these upper rocks and found small crevices between them, some large enough for us to insert our arms up to the elbow.  We then inserted a flexible metal tape measure in a number of these crevices and found that the length it went in matched that between the circular plinth at the base of the trig and where these upper rocks had been positioned.  This indicated that the circular plinth was solid, rather substantial and no doubt man-made, it was this that the metal tape was reaching when it would not go further in to each crevice, this indicated that it was the circular plinth that had been constructed over the ‘natural’ summit tor. 

John getting to grips with the outer section of the mound that surrounds the summit plinth

Somewhere in here is the high point of the summit tor

Our next objective was to set up the level on the circular plinth beside the trig pillar and attain readings to a number of the higher rocks of the tor, this meant that Graham had to position himself delicately on the outside of the ‘mound; whilst holding a surveyors staff, vertically aligned for John to read out figures on the staff from the level, which I noted.  This was repeated on a number of ‘natural’ rocks around the upper section of the ‘mound’.  We then took readings to the top of the trig pillar, its base and also to its flush bracket.  These we could compare to data that had been collected from the top of the trig pillar using the Trimble GeoXH 6000.  

The Trimble gathering data from the top of the trig on Yr Wyddfa

All of this was being filmed by Aled, whilst a multitude of people marched up the steps either side of the summit ‘mound’.  The realisation soon dawned on us that the survey would probably have to take place in the evening or early morning as we had difficulty operating the level purely through the amount of people visiting the summit.

John with the level as another summit visitor poses for a photo

Graham balances on the periphery of the summit plinth with the staff as Stephen looks on

Once satisfied that our first recce had accomplished more than we had hoped, we headed for the café and more tea.  By this time there were signs that the predicted break in the weather with the mist forecast to disperse and sunshine breaking through was just about to happen, and as we left the café on our way toward Crib y Ddysgl the mist was ripped from the summits, blue sky appeared and the world outside showed itself.

Aled filming a passing train as we head toward Crib y Ddysgl

Although our priority for the day was the reconnaissance of the summit of Yr Wyddfa, we wanted to take the opportunity and also survey Crib y Ddysgl, which is listed as the second highest mountain in Wales with a summit height of 1065m.  However, to its north in the range of mountains known as the Carneddau lies Carnedd Llywelyn, which has a map height of 1064m, and with a margin of uncertainty of + / - 3m applied to the surveying method that attained the latter height, it meant that Carnedd Llywelyn may in fact be higher than Crib y Ddysgl.

The team assembled (L-R) Stephen Edwards (Producer), Aled Llŷr (Director), Graham Jackson
(Surveyor) and John Barnard (Surveyor) and there's another surveyor behind the camera; me

Once on its summit we found the highest point with the aid of the level and staff.  The Leica GS15 was positioned over it and we gathered two hours of summit data.  By now blue sky shone from above with the clarity of colour enjoyed and although I’d seen the view across to Yr Wyddfa from this position on many occasions, it still proved awe inspiring as its great wedge of eastern face shot up to the pointed summit, all enhanced by the perspective of tiny figures on its summit and the upper part of the Llanberis path.

The Leica GS15 on the high point of Crib y Ddysgl

Aled filming as Graham explains the intricacies of surveying

As the equipment was packed away we headed down and on to the Llanberis path with Llechog in front of us and the Glyderau across the Afon Nant Peris to our right.  We had a thankful rest and cup of tea in the Halfway House café, meeting Alwena Jones who is one of the five people who Stephen and Aled are following for ‘The Mountain’ programme.  I stayed a few minutes chatting with Alwena as Stephen, Aled, John and Graham headed down.  My descent was on my own, as however fast I tried to walk there seemed no way of catching the others, after a few minutes I settled in to a comfortable pace and spent the next hour admiring the greens on the Moel Eilio ridge as the late afternoons light shone vivid, accentuating the beauty of the hills. 

Heading down from the hill

Postscript

Since the summit survey of Crib y Ddysgl 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 this hill has been analysed using this technique, resulting in the LIDAR height and position for its bwlch being used.

Survey Result:

Yr Wyddfa

Summit Height:  1084.8m (converted to OSGM15) (Ordnance Survey historical data to bedrock at summit)

Summit Grid Reference:  SH 60985 54374 (Old Triangulation Pillar and Ordnance Survey historical data to bedrock at summit)

Bwlch Height:  47.6m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  NS 75797 78295 (Trimble GeoXH 6000)

Drop:  1037.2m (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

Dominance:  95.61% (Ordnance Survey historical data to bedrock at summit and Trimble GeoXH 6000 bwlch)

Trimble GeoXH 6000 survey from 05.06.14: 1085.673m (converted to OSGM15)

Trimble GeoXH 6000 survey from 02.09.14: 1085.716m (converted to OSGM15)

Leica GS15 survey and processed with Ordnance Survey Bernese Software:

1085.716m (converted to OSGM15)

Ordnance Survey Result from 1961 Survey to High Point of Bedrock:

Natural High Point:  1084.74m (not converted to OSGM15) and 1084.786m (converted to OSGM15)

Crib y Ddysgl

Summit Height:  1065.4m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SH 61079 55154 (Leica GS15)

Bwlch Height:  990.9m (LIDAR)

Bwlch Grid Reference:  SH 60775 54849 (LIDAR)

Drop:  74.5m (Leica GS15 summit and LIDAR bwlch) 

Dominance:  6.99% (Leica GS15 summit and LIDAR bwlch)

For details on the 2nd summit survey of Yr Wyddfa

For details on the bwlch survey of Yr Wyddfa

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