02.09.14 Yr Wyddfa
(SH 609 543)
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| Yr Wyddfa (SH 609 543) |
Following the 5th 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 2nd
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.
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| 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.
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| 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.
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| 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.
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| The pillar plate on top of the trig pillar |
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| The Trimble GeoXH 6000 and the Leica GS15 both gathering data atop Yr Wyddfa |
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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 bwlch survey of this hill
For further details please
consult the Trimble survey spreadsheet click {here}
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