Sunset on Snowdon's summit. Photo: Myrddyn Phillips

Have you ever wondered why Scotland and England’s highest mountains are blessed by two summit heights on Ordnance Survey maps?

Both have what OS considers man-made additions to their tops, and the lower of the two figures is the height of the ‘natural’ bit of the mountain rather than the height of the artificial cairn, which is in brackets.

But we all climb those cairns anyway, don’t we?

Well, it could be that Wales’s highest peak Snowdon might be about to join Ben Nevis and Scafell Pike in the same bracket club.

At first it appeared Yr Wyddfa might be up for a metre’s worth of promotion, but Britain’s national mapping agency is very strict about what constitutes a mountain’s top.

The trio of amateur hills sleuths who lug their very professional GPS measuring equipment to various mountains had their eye on Snowdon for a while. John Barnard, Graham Jackson and Myrddyn Phillips escaped the Snowdonia crowds for a night on one of the UK’s best trodden peaks.

This is their story of how difficult it is to get to the bottom of what is the highest point in Wales.

Snowdon is one of the most iconic mountains in Britain. More than 400,000 people a year find their way to its summit; it is also one of the most visited mountain tops anywhere in the world. It is also a mountain top that has experienced man’s intrusion on a multitude of occasions.

Man’s interference with the summit area of Snowdon is centuries old as legend has it that the mountain’s Welsh name of Yr Wyddfa is associated with the burial mound of a giant named Rhita Gawr.

In more recent times the Royal Engineers built a substantial cairn on the summit which was added to later in the 19th century. Early photographs from the time show this cairn as a huge neat pile of stones dwarfing people sitting on its top and vying for dominance over the summit buildings that had started to appear on Wales’s highest mountain.

Snowdon: the height remains the same, but the climb just got bigger. Photo: Myrddyn Phillips

These summit buildings which were once described as ‘hotels’, at one time one stood opposite another as vast tracts of the summit area were levelled to site each building. Victorian visitors rode to the summit and stables were built there to accommodate their horses.

Then along came the mountain railway and the later addition of a summit cafe which greatly expanded the accessibility of this already popular mountain.

The present summit cafe Hafod Eryri was opened in 2009 with great fanfare as befits this granite edifice. During the time of its re-construction from the previous concrete building that adorned the summit area for many a year, the high point at the summit of the mountain also underwent a make-over.

This make-over was substantial with the old trig pillar being replaced with a rounded version and accompanying brass panoramic viewfinder.

This viewfinder was especially installed for when the weather is inclement as visitors can peer out into the cloud and mist to where distant land in Ireland and the Lake District could be seen if it were clear and sunny.

It wasn’t just the trig pillar that was re-fashioned but this whole area too, resulting in two walkways leading up to a newly built summit plinth that could accommodate the thousands of visitors that swarm over the summit every year.

Man’s tampering at the summit of Snowdon set a new challenge to the trio of hill sleuths at G&J Surveys. John Barnard, one of the surveyors who re-heighted Snowdon said: “We wanted to measure the height of Snowdon with our Leica GNSS receiver for a number of years and the opportunity to do so presented itself five months ago.”

The trio of independent surveyors was approached by Stephen Edwards and Aled Llyr, head of Cread Cyf and Slam Media respectively.

Aled Llyr capturing the scene on Snowdon. Photo: Myrddyn Phillips

Mr Edwards said: “We are currently filming a six-programme series named The Mountain for ITV Wales which follows five people and how the mountain of Snowdon affects their lives.”

These five are 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 cafe.

Aled Llyr from Slam Media said: “The programme is due to be broadcast early next year and knowing Stephen’s past association with G&J Surveys when he joined them on the survey of both Tryfan and Glyder Fawr, we always knew that a resurvey of Snowdon with their GNSS equipment would fit nicely into the programme about the mountain.”

The trio of surveyors, Mr Edwards as producer and Mr Llyr as director were joined by Mark Greaves, the geodetic analyst from Ordnance Survey, who was present during the survey to put the official stamp of approval on proceedings.

Graham Jackson said: “We visited Snowdon in early June of this year as part of a reconnaissance and this proved vital as we wanted to acquaint ourselves with the details of the summit area.”

It was through this trip that the hill sleuths decided that the survey itself would have to take place without disturbance from the throngs of summit visitors.

From left: Graham Jackson, Mark Greaves of OS and John Barnard beside the Leica GS15 at the top of Snowdon. Photo: Myrddyn Phillips

The expedition members took the 4.30pm train on Tuesday 2 September and camped in the café overnight, with prior permission from the Snowdon Mountain Railway, which leases the building from the national park authority.

This enabled the survey to take place when all the train passengers had departed the summit.
Once the summit was clear of the multitude, they used a Leica automatic level and staff to ascertain the high point at the summit plinth and also to determine the highest ‘natural’ rock that was visible on the periphery of the plinth.

John Barnard said: “We had studied old photographs of the summit area from the late 1800s through to the early 2000s and by doing so we had a comparison of rock formations that appeared in each photograph. These were compared with photographs we took on the recce and we now pinpointed where each rock was and took a relative height reading to it with the level and staff.”

By doing this, the hill sleuths were able to measure a height difference between the high point of the summit plinth and the highest ‘natural’ rock.

Myrddyn Phillips said: “Thankfully the weather was favourable and after pinpointing the position of the highest point of the summit plinth, we set up the Leica equipment on its 2m pole which was well supported with a tripod. It was then left in place for three hours to collect the all-important data.”

The team slept in the cafe and early next morning they took another three-hour data set from the exact same position, with the tripod and 2m pole having been left on the summit during the night.

Walkers heading for Snowdon's summit, and the extra metre's climb. Photo: Myrddyn Phillips

The team had the equipment up and running and gathering data at 5.20am, and then relaxed while watching a stunning sunrise over Moel Siabod to the East. At 8.20am the second three-hour data set had been completed and the equipment was then switched off.

Through study of old photographs and the measurements taken around the periphery of the summit plinth, the hill sleuths had determined that the top of Snowdon’s summit tor, that is the natural summit, is buried about 80cm below the summit plinth at the base of the trig pillar.

The two three-hour data sets from the survey of Snowdon were combined into one which Mark Greaves later post-processed using Ordnance Survey software. This gave a height of 1085.67m.

This means that the natural summit is about 1,084.8m high or 1,085m rounded to the nearest metre to conform to mapping convention.

So although the natural bedrock and the Ordnance Survey map height of 1,085m will remain the same, all those thousands of hillwalkers who struggle up what they think is a mountain of 1,085m in height are in effect climbing one extra metre and arriving at the top of Snowdon peering out on land and sea that is 1,086m below them.

ITV Wales is due to broadcast a half-hour programme about the survey, Snowdon – Climbing New Heights, at 7.30pm today.

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