The Arnales peak, a three-thousander (Part Two). The solution.
Perhaps some of you who follow us often remember the article we dedicated to Arnales: The Arnales Peak, a three thousand?. This is one of those peaks that verge on the three-thousand-metre barrier and which in some publications is included in the list of three-thousand-metre peaks, while in others it is left out. Well, in that first article, after carrying out a small study of the summit area in which we used lidar data, the same data used to make the official cartography, we ended up as follows:
Although it is not possible to state categorically that Arnales is higher than three thousand metres, in the lidar point cloud, the basis for obtaining altitudes in mapping, there are data that clearly indicate that it is a three thousand, being 3000.42m high.
A check that will be practically definitive in the future will be possible when the flight data from the second Lidar coverage, accurate to 20 centimetres, are published. In the meantime, the only option to resolve this issue definitively is to go up with a dual-frequency GNSS receiver and take measurements with an accuracy of less than 5 centimetres.
Well, a few months later, a group of 5 topographers under the name of "Sostremetries", have completed the task, reaching the summit of Arnales with one of these receivers and obtaining centimetric precision (7 cms). Without further ado, we leave you with the story that this group has given us of that trip, which is nothing more than the culmination of a larger project that will be officially presented at the Vic Book Fair in early November.
Measuring peaks with precision: Arnales, another three thousand!
- What do we do, do we climb this peak too?
- Oh no, it's not worth it, it doesn't reach three thousand metres.
- On my map it says yes, it is 3006 m!
- According to the cartography of my map it is 2996 m.
- Wait for it! My GPS says...
- ...
More than one of you will be familiar with this type of conversation. Collecting three-thousanders in the Pyrenees makes many hikers question whether a peak is worthy of being climbed or not according to this label. In fact, it is not unusual to find discrepancies of more than 5 m in the height of a peak, even on the most emblematic ones. The height of the vast majority of Pyrenean peaks has not yet been accurately measured.
At the end of the 1980s, an experienced team of Franco-Spanish mountaineers adapted a set of rules for the cataloguing of summits used in the Alps for summits over 4,000 metres, with the intention of drawing up and reaching a consensus on a list of the Pyrenean three-thousand-metre peaks that was as objective as possible.
Broadly speaking, these rules for the Pyrenees distinguished between main and secondary summits, where a minimum prominence of 10 m was required and the toponym had to appear in a previous publication. As a result of this first cataloguing, in 1995 the UIAA adopted the criteria and officially recognised 129 main summits and 83 secondary summits. Towards the end of this internationally recognised list we find Pico Arnales (in the municipality of Panticosa, in Aragón) with a height of 3006 m.
On the other hand, the National Topographic Map 1:25,000 published by the National Geographic Institute (IGN) shows Arnales at an altitude of 2,996 metres. Ten metres less than the value published by the UIAA and thus no longer a three thousand! As if this were not enough uncertainty, the Geographic Institute of Aragon (IGEAR) publishes through its portal of
vectorial cartography up to scale 1:5.000, where the same summit appeared until a few years ago with a height of 2999.9 m and that recently and without reporting new measurements they have rounded up to 3000.0 m as it also appears in the ORDEN VMV/914/2020 of the Official Gazette of Aragon.
So what is the real height of Arnales Peak and what is the most reliable source? More importantly, is it a tresmil?
With the intention of resolving the dilemma, a team of five topographers under the name of "Sostremetries" decided to take the search a step further by analysing the methodology used on each of the published peaks. A consultation of the publications of the group of mountaineers who call themselves "Ghostbusters" confirms that the Arnales Peak is
a good candidate to be investigated. Since the 1:5000 cartography published by the IGEAR gives a value of just 3000 m and with an accuracy of the order of 1 m, more reliable sources must be sought. This is where the point clouds generated with LIDAR technology, which the IGN publishes under the PNOA-LiDAR project, come in. Within this point cloud we find four return signals sent against the terrain that report an altitude of over 3000 m, the highest of them at 3000.42 m. Although these points have a height accuracy in the order of 30 cm, it is most likely that none of them bounced exactly over the summit if we take into account that they take a point every 2 m2. On the contrary, the returns mentioned could have come from a pile of unconsolidated stones, a hypothetical cross, the head of a hiker or even a bird flying over the summit at the time.
At this point, the Sostremetries team decided that the only way to solve the dilemma was to organise an expedition to the summit and measure it with centimetre-precision topographic devices, thus applying a methodology that they had already used successfully on other peaks in the Catalan Pyrenees.
And so it was midday on 30 July 2022. Marc Calaff, with the car loaded with topographic instruments, picks up Andreu Alvarruiz at work and they pass through Sabadell. With David Segura in the car they head to the meeting point where Salva Sala will arrive, because this time Oriol Boixareu will not be able to accompany us either. It was a difficult decision since the project was started by the five of us, and now it seems so close to achieve the milestone of finding a "tresmil", but it has been impossible for us to fit it into another weekend. So it was with a mixture of emotion and regret that we crossed the country horizontally towards the Aragonese Pyrenees.
The journey is very pleasant, and as we calculate the food and drink to buy, the excitement builds until we reach Panticosa. We are only a few hours away from resolving an insignificant doubt, but it makes us feel like the first topographers-alpinists who mapped emblematic mountains, some of which still bear their names today.
Having a drink while we prepare dinner, Marc makes the last tests with the GNSS receiver, checking that it is well configured to work in Aragon. It is not usual for us to go out to work too far away from our territorial area, and this is the first time that we will connect to the ARAGEA network to be able to work in VRS.
obtaining data in real time.
After a hearty plate of pasta for dinner, we draw lots for the rooms to determine once again that David will share a room, this time with Salva. Marc will be able to choose the bunk bed in his room, and Andreu will sleep wide and alone in the double bed. We do the last check on the batteries of the equipment, distribute the weight between the backpacks and go to sleep, tomorrow will be a day to remember.
It is 7 o'clock in the morning and we are just finishing breakfast, even though the weather forecast is favourable we should not get too excited, so we fill our water bottles with water and head for the car. We still have 15 minutes drive to Baños de Panticosa.
Once we reach the Ibón de los Baños, which welcomes us at an altitude of 1640 m, we enter the labyrinth of camper vans that fill the area in search of a place to park in anticipation of the shade we will seek in the afternoon. There are a lot of people, and it seems that they have all decided to wake up at the same time, we see some running to hide behind a pine tree, people who barely half open their eyes to contemplate the immensity of the mountains that have sheltered them during the night, and above all a delicious smell of coffee. And if there was any sense left to awaken, it was smell. Now with everything ready, we set off for the summit.
It is after 9 o'clock in the morning and we have to make our first stop, the difference in altitude we have overcome in the forest has not been much and the sun has been beating down hard since we left it behind. We hide in the first shade offered by the first small wall that we will try to overcome through a gap at an altitude of 2300m. Soon the last groups of people that we had overtaken are taking over the lead again, so we start to get back on our feet.
We smear sunscreen on the back of the neck and the tips of our ears, take a drink of water and get back on the road.
The path, which during the forest was not entirely clean, with branches and some fallen trees, now allows us to climb steadily despite the steep slope, and Andreu and Salva are marking relays at the front of the group maintaining a good pace that soon puts us back in contact with those last groups with whom we greet again.
The landscape is marvellous and we all agree in imagining it in the solitude of winter, well covered in powder snow, and at this time of year it is difficult to find a window to frame a photograph that does not show groups of people progressing towards a peak in the area. Arriving at the Pondiellos pass, finally
We spotted our goal. We are still a little less than 200 m of vertical drop below, but with our pace of 500 m of elevation gain per hour we have earned a second break to eat something more and talk to the rest of the groups that are arriving. In front of our eyes, looking down a little, we have the Pondiellos lakes, and just behind them, looking up, the trilogy of three peaks of the Picos de los Infiernos, with its south-southeast wall that joins the Infierno Occidental with the Pico Infierno Central and the Infierno Oriental, which from this perspective seems completely smooth and bestially vertical. To its right is the Garmo de Pondiellos, also popularly known as the Aguja de Arnales and also more than three thousand metres high and over 10 m in prominence, but with a height of more than ten metres.
with only two edges. And then the pass towards which we are heading.
Before the next group arrives and we explain once again why we are carrying such a large tripod out of our backpacks, we resume our walk through the shadow cast by the Pico de Pondiellos, going gently up a diagonal through granite terrain until we reach the foot of the vertical of the pass towards which we are heading. At this point we must focus on what we are doing and stop looking towards the siren songs coming from the Pico de Arnales, and the fact is that the number of people who come and go walking through the area means that small rockslides paralyse the groups in this cul-de-sac, with everyone trying to make out that theirs is not the position where the imminent danger lies.
Without any further scares, with the change of views brought about by the arrival at the col, we now follow the ridge parallel to the highest point of Pico de Arnales. From the slope from which we have arrived it is a fairly comfortable peak despite the rocky crumbling that makes it up. As far as the traffic is concerned, at the tartera we have already separated from the large flow of people heading towards Los Infiernos. Shortly afterwards those looking for the Aguja de Arnales have also left them behind and it seems that only those heading towards Arnales Sur pass this way. So we comfortably spread out our rucksacks, trying to delimit a work area and Marc immediately switches on the GNSS receiver and starts to pick up satellite signals.
Salva carefully prepares the optical level by attaching it to the tripod while Andreu locates the highest consolidated points in the area. He has had to move a lot of stones broken by the passage of time and inclement weather to discover them so that David could rest the sight on which Salva checks the height. We easily located the highest point of the summit, now the problem is an old acquaintance of our sostremetrias, the mobile coverage necessary to establish connection with the differential corrections service of the ARAGEA network provided by IGEAR to be able to have figures and coordinates in real time of what we are measuring.
Despite the variety of phone companies between the four of us, none of them are giving us sustained coverage in this area, so we decide to eat our sandwich and then continue scouring the few square metres of the summit area for mobile data.
Although we are reluctant to leave the summit without giving it a real time height, it has been more than two hours since we reached the summit and we are still the same. We start to get nervous because the afternoon is upon us, and it is 14:30 and we still have the way back. We see less and less people approaching the other summits, the trend is now downwards.
So it's time to implement plan B, dispense with the real-time solution and make a static observation for a minimum of 30 minutes and post-process it at home. Without a second's hesitation, Andreu firmly grabs the GNSS receiver and with David's help they position it exactly on the highest point of the summit. Andreu keeps his eyes on the spherical level that acts as a plumb line to guarantee the verticality of the pole, David fixes the tip of the pole so as not to lose his position, and Salva holds Andreu like a prop to stabilise the situation. Luckily it is not a windy day and the weather is still favourable. With this picture, Marc sings the minutes that are falling and the satellites that are entering and leaving the constellation.
We have the work done but we are not satisfied, it seems that we will not know the height until we get home once we have done the post process. The only thing left to do is to immortalise the movements and that's why Salva takes out his camera. The images are spectacular, the perspective of this small peak at the foot of Los Infiernos is unbeatable, but we can't dedicate too much more time to it, so while we pick up the optical level and the tripod, Marc insists on doing one last test. Nothing at all.
That's when Andreu's mobile phone receives a series of Whatsapp messages and the idea of sharing data from his mobile phone to the GNSS receiver comes up. Marc starts to change settings while David stays still holding the phone, as if he could keep the data connection better. We've got it! After more than three hours on the summit, 3 minutes of connection with ARAGEA was enough to get real time corrections, 3001.565 m.
For our project it is not yet a definitive figure, but taking into account comparisons of data obtained in real time with data obtained in static with post-processing in previous sostremetries, we know that the value that we will obtain in dimension will be similar, therefore, we can go home with the peace of mind of knowing that it will be above the
three thousand metres.
The last three minutes have concentrated the effort, the emotion and the desire to do something for our esteemed profession that has made the journey here worthwhile, and this time the mountain has rewarded us pleasantly by revealing its true peak.
Three hours down to the car, calls to Oriol and the respective families to give the news that everything had gone well and a drive back home are reduced to this paragraph. What interested us all now was the outcome of the post-processing.
We contacted Isaac, a university colleague who has specialised in satellite navigation systems for years, to give us a hand and to refresh some concepts of post-processing of static observations. In our day-to-day work as surveyors we don't often use this technique and we are a bit rusty with it. The post-processing is also a success, confirming that the differences in elevation are less than 20 cm with respect to the elevation obtained in real time.
Finally, a comparison between the systematic errors associated with each of the two methods used leads us to opt for the figure obtained in static and with an accuracy of around 7 cm.
Orthometric height Sostremetries Arnales Peak 3001.37 m.
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The number of three-thousand-metre peaks, those that comply with the rule of exceeding three thousand metres in altitude and having a prominence of more than 10 metres, is not definitive. Among these mountains that are in limbo we find the case of Arnales, included in some lists and left out in others.
