Ordnance Survey Blog Post - Re-surveying Snowdon

Ordnance Survey recently published a post on their Blog about the survey of Yr Wyddfa / Snowdon conducted by G&J Surveys.  The original Blog post and a link to it on the Ordnance Survey website appear below.

The survey of Wales’ highest mountain was covered in an ITV Wales programme broadcast at 7.30pm on Tuesday 14^th October 2014 and entitled ‘Snowdon: Climbing New Heights’.

The survey benefited from the help given by a number of people and organisations.  Thanks to Stephen Edwards (CREAD Cyf, Producer), Aled Llŷr (Slam Media, Director), Mark Greaves and the Ordnance Survey, Snowdon Mountain Railway and ITV Wales.

Re-surveying Snowdon

Regular blog readers will have come across Myrddyn Phillips and his intrepid team of mountain measurers from G&J Surveys previously.  Their latest challenge focused on Snowdon and on Tuesday 2^nd September, Myrddyn’s team and our own geodetic expert Mark Greaves, set off up Wales’ highest peak along with a film crew.  The re-survey was being covered by ITV Wales as part of their programme ‘The Mountain’.

The eastern face of Snowdon

Luckily for the team, with their huge amount of filming and surveying gear, they could catch the train to the summit late in the afternoon.  Once atop the peak, they started the challenging process of identifying the spot to carry out the resurvey.  At Ordnance Survey, we prefer to identify the natural summit of a mountain to measure the height, and this was the basis that we originally measured the mountain.  Since this time, a plinth had been built on top of the natural rock and the survey needed to be carried out from the plinth as this was the closest location to the natural summit which could be accessed and surveyed.

Once the survey equipment was set up, the team settled down for a night on the mountain whilst the data was captured over a number of hours.  You can see some of the spectacular views the team enjoyed in the pictures they captured during their trip.

Mark brought all of the data back to our Southampton head office to process and confirm.  You’ll be able to see the results for yourselves on ITV Wales tonight at 7.30pm in ‘Snowdon – Climbing New Heights’ as well as early next year in ‘The Mountain’.

As you’ll see in the programme, we’ve preserved the original height of the natural summit of the mountain and retain the value 1085m on our maps.

You can also find out more about Myrddyn’s experiences in his guest blog.

The re-survey of Snowdon

 

In Wales Snowdon stands supreme above all other mountains, the highest in the land.  In the British Isles it is also the highest in the combined lands of Wales, England and Ireland and you would have to journey to the Scottish Highlands before something of equivalent height is encountered.

The mountain is architecturally one of the finest with a series of almost symmetrical ridges leading down from its summit in dramatic fashion, providing some of the best hill walking country anywhere in Britain.

The mountain is also steeped in legend.  Its Welsh name of Yr Wyddfa, is associated with the burial mound of the giant named Rhita Gawr, and the col to the east of the summit, Bwlch y Saethau, is the legendary site of King Arthur’s last battle.

As well as a mountain of myth and legend it was also a mountain that we had contemplated surveying for a number of years with the latest survey-grade GNSS receiver.

The opportunity to do so presented itself a few months ago when we were approached by Stephen Edwards who is the head of CREAD Cyf and Aled Llyr the head of Slam Media.

Stephen and Aled were in the process of filming a six programme series for ITV Wales named ‘The Mountain’ due for broadcast early next year.  This programme will concentrate on five people, a hill farmer, the Head Warden of the Snowdonia National Park, a train driver on the Snowdon Mountain Railway, a member of the Llanberis mountain rescue team and the owner of the Halfway House café, and it will show how the mountain of Snowdon affects their lives during the seasonal change through the year.

Stephen knew of our plans to re-height Snowdon and asked if we wanted to do so as part of this programme.  We jumped at the chance!

The major difficulty with surveying Snowdon is that the summit area of the mountain has been affected by man’s intrusion.  This intrusion has taken the form of a large cairn first built on the summit by the Royal Engineers in the early 1800’s.  This cairn was added to and in time became a huge pile of neatly packed rocks that appear in some of the early photographs of the summit from the late 1800’s.  At one time there were two competing ‘hotels’ placed at the summit and their construction meant tracts of the summit area were levelled to accommodate each building.  The Victorians then built a railway to the top of the mountain and in more recent years the summit café at the railway terminus was also built.

The summit area has recently undergone another transformation when in 2009 the new café which is named Hafod Eryri opened to the public.  It was at this time that the actual summit of the mountain was also transformed when the old standard triangulation pillar that formed part of the last accurate survey of the mountain in 1961 was replaced with a circular trig pillar with an accompanying brass panoramic viewfinder.  The major transformation was the building of a summit plinth that could accommodate the multitude of visitors.  This summit plinth is circular and relatively flat not withstanding its cobbled stone surface.  It is a work of art that must have taken a tremendous amount of time to build, but by doing so the natural high point of the mountain was buried under its surface.

We visited the summit in early June for a reconnaissance and this proved vital as attempting to survey in front of a camera without prior knowledge of the area of the summit was not to be recommended.  After the reconnaissance we approached Ordnance Survey and outlined our plans.  Ever supportive, Ordnance Survey liaised with Stephen, Aled and ourselves and suggested that Mark Greaves may like to join us on the day of the survey to oversee proceedings.  Mark is the Geodetic Analyst at Ordnance Survey and one of the leading experts on GNSS technology in the country.

Because of the recent transformation of the summit we sought advice from Ordnance Survey who instructed us to take the measurement from the base of the triangulation pillar and this could then be compared to the 1084.74m height obtained in 1961 which was to the highest bedrock of the mountain.

Stephen arranged with the Snowdon Mountain Railway for transport up and down the mountain as we had a mound of gear that needed to be hauled to the top.  On Tuesday 2^nd September we met at the adjoining car park to the Railway Station and headed up the mountain on the 4.30pm train.

Prior to departure on the 4.30pm train upto the summit

Once at the summit we waited for the passengers to leave on the last train down the mountain before venturing out to start surveying the summit area.  Thankfully the forecast was ideal with wind speed no more than 15-20mph which lessened as the evening progressed.  It was cloudless and visibility was excellent, and as we used a level and staff to ascertain the highest point on the summit plinth, the sun crept ever lower heralding a beautiful sunset.

There were a number of options how to survey the summit, one was using a pillar plate

We positioned our Leica GS15 at the highest point of the plinth and set it gathering data at 8.00pm.  Mark had suggested that we could gather two data sets, one in the evening and another in the early hours of the morning and we decided to gather three hours during each timeframe, resulting in six hours of data in all.

The Leica GS15 set up at the top of the summit plinth

By 11.00pm the first data set had been collected and we had time to gaze at a sky that was full of stars with the Milky Way stretching across the heavens.  Considering the evening was so beautiful it was miraculous that, except for us, no one visited the summit during these three hours of data collection.

Stephen had also arranged that we could sleep overnight in the summit café and as the night proved so tranquil, we left the tripod and two metre pole in place overnight so that when we headed back to the summit for the morning’s data collection they were positioned in exactly the same spot.

We gathered data between 5.20am and 8.20am to get the six hours we wanted and during our vigil we hoped to be treated to a memorable sunrise.  As we waited a bank of grey cloud slowly edged itself westward and when the sun made its appearance it quickly disappeared behind the cloud.  We thought this a little disappointing, but then to our surprise the next hour proved stunning as the sun’s rays broke through the cloud turning the land to our east around Moel Siabod delicate shades of red and orange.  Wisps of mist ebbing ever upward from the valley below caught the glowing light and presented us with a breath-taking picture.  It was an unforgettable spectacle.

Early in the morning and the second data set is gathered as the sun rises

Sunrise over Moel Siabod from the top of Snowdon

We departed the summit on the 9.00am goods train happy in the knowledge that we had gathered six hours of data which Mark would later process.  A few days later and Mark had obtained the result from the summit plinth, this came to 1085.67m.

The Ordnance Survey will adhere to the protocol of listing the height of Snowdon 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; Snowdon / Yr Wyddfa 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 1086m below them!

Left to right:  Aled, Graham, Mark, John and Stephen during the three hour morning vigil

ITV Wales are broadcasting a half hour programme about the survey entitled ‘Snowdon – Climbing New Heights’ which will be shown at 7.30pm on Tuesday 14^th October.

The survey of Snowdon will also form part of the six programme series entitled ‘The Mountain’ which is due for broadcast early next year on ITV Wales.

John Barnard, Graham Jackson and Myrddyn Phillips

Wondering what the height was going to be as we arrived at the summit cafe prior to the survey

Please click {here} and {here} to see the original post published on the Ordnance Survey Blog