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Mont Blanc 2026: 4,807.47 m
Mont Blanc 2026: 4,807.47 m
Mont Blanc 2026: 4,807.47 m
Mont Blanc 2026: 4,807.47 m
Mont Blanc 2026: 4,807.47 m

Mont Blanc 2026: 4,807.47 m

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Mont Blanc 2026: 4,807.47 m,
and a first glimpse beneath the ice

On 14 October, in Saint-Gervais, the French Expert Surveyors unveiled the new altitude of Mont Blanc:
4,807.47 metres.
But the real novelty of this 2026 campaign lies elsewhere: for the first time, the chartered surveyors have measured what lies beneath the ice.

TERIA was at the summit. Here’s our report.

We don’t measure snow; we measureice

Since 2001, French Expert Surveyors have been climbing Mont Blanc to measure it, and they now do so every year. And each time, the figure changes:

4,810.90 m in 2007,
4,805.59 m in 2023,
4,807.47 m in 2026.

An important point to note: what is being measured is not a pile of fresh snow. At the summit, the snow that manages to settle compacts and turns to ice. It is the highest point of this ice cap, resting on the bedrock, that the French Expert Surveyors measure. And this ice cap is a living entity: the wind sculpts it, precipitation thickens it, and hot summers compact it.

This explains a fact highlighted by the data series: the September measurement is always higher than that taken in spring. In winter, the wind blows too strongly at the summit for the snow to settle there and turn to ice. It is in spring and summer that the ice cap replenishes itself.

Result for 2026: 1.88 m compared with 2023, and a figure just 27 cm short of that calculated by the Vallot cousins in 1894. The results for 2024 (4,808.51 m) and 2025 (4,808.76 m), which had been kept in reserve, were revealed at the same time.

The summit does not just vary in height.
From one year to the next, the highest point also shifts along the ridge line, swinging sometimes towards Chamonix, sometimes towards Saint-Gervais, depending on the prevailing winds.

On 17 September, at daybreak

The summit attempt was scheduled for Thursday 17 September, following several days of waiting for the weather to improve.

A night-time set-off, a 10-hour climb, 2,500 metres of elevation gain, 11 rope teams and 32 people: surveyors from Haute-Savoie, as well as from Isère, Rhône, Haute-Garonne, Landes and elsewhere; high-mountain guides; technical support staff; a photographer; and a film crew.

In their rucksacks, nearly 30 kg of scientific equipment in addition to their mountaineering gear.

At the summit, two hours. Two hours in the wind, at over 4,800 m, setting up the instruments, taking one measurement after another and making sure nothing was forgotten – because there’s no going back down to take another measurement.

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What TERIA did up there

The ground targets, measured using the PYX-i, are used to calibrate the 1,300 images captured by the drone.

As a technical and financial partner of the expedition since 2008, TERIA enables centimetre-level positioning of everything measured at the summit. This year, this involved three missions.

The summit, in a matter of seconds
On its own, a GNSS receiver (also known as GPS) can only determine its position to within a few metres. With corrections sent in real time by TERIA’s QNRTK network – comprising more than 250 stations spread across the country – it achieves centimetre-level accuracy in a matter of seconds, even at 4,800 metres.
To measure how far we’ve come: in 2001, it took 1 hour 40 minutes in a storm just to obtain a single point.

The drone: 55 cm more accurate
The drone captured over 1,300 images of the summit, which were assembled into a 3D model comprising 15 million points. This point cloud remains floating in space until it is anchored to physical points on the ground. Even with an RTK drone, which allows for precise positioning of the images captured, this becomes complicated in extreme conditions. And it is necessary to combine technologies to achieve greater accuracy.
This is the role of the ground control points, measured using the PYX-i, in its very first high-altitude deployment. The result: an improvement of 55 cm in accuracy across the entire model.

Ground-penetrating radar, positioned to the nearest centimetre
For the first time in 15 French Expert Surveyors, a 6 kg ground-penetrating radar unit was carried and towed across the ice cap along profiles of over 100 m, repeated around fifteen times. Each pass was positioned to the nearest centimetre using the TERIA network. Without a precise position, a dynamic depth measurement cannot be carried out: we would know how much ice there is, but not where, and the data would become mixed up.

Beneath the ice: what we knew, what we ’re discovering

The idea of looking beneath the summit is not a new one. On 25 May 2004, the glaciologist Christian Vincent, from the Grenoble Laboratory of Glaciology and Environmental Geophysics (LGGE), had surveyed the ice cap using radar. He then pinpointed the rocky summit at 4,792 m, some forty metres to the west of what was, at the time, the snow-covered summit.

In 2026, for the first time, the French Expert Surveyors were able to see beneath the ice themselves, using their own methodology. By cross-referencing the surface area measured by drone with the depth measured by ground-penetrating radar, the bedrock was successfully modelled during this expedition. Directly beneath the snow-capped summit, the ice is 24 metres thick. Across the ridge, its thickness varies from around 30 metres on one slope to 20 metres on the other.

Contrary to what one might think, the summit we stand on is therefore not directly above the rocky summit. Along the ridge, the highest point of the modelled rock rises to 4,789.40 m, beneath 16 m of ice, 83 m from the snow-capped summit.
Between the two, the rock remains almost flat: it is the ice, sculpted by the wind, that forms the highest point.

And the story is undoubtedly not over yet. The highest point of the modelled rock lies on the edge of the surveyed area, and the rock could continue to rise beyond this point, which would match the elevation of 4,792 m recorded in 2004.

‘The Mont Blanc of ice’ and ‘the Mont Blanc of stone’ are therefore not in the same place.

One question remains: the rock itself does not move. If the measurements from 2004 and 2026 do not give exactly the same altitude or the same offset, it is because the areas surveyed, the equipment, the reference points and the protocols differ. Other teams have also surveyed the ice cap: the Montagne Sûre Foundation, on the Italian side, in collaboration with the CNRS’s EDYTEM laboratory, launched a drone and ground-penetrating radar campaign in 2025 to measure the ice thickness, the results of which have not yet been published.

For the next campaign, the aim is clear: to liaise with these teams to understand which instruments and protocols were used, and to what level of accuracy, in order topool the results and consolidate a shared understanding of the summit.

The partners have also been innovative

This was a collaborative effort, and everyone made a contribution.
The IGN, the other key to determining altitude.
has, for the first time, carried a 5.5 kg gravimeter to the summit to measure gravity, on which the calculation of altitude depends: 9.794 m/s² on Mont Blanc, compared with 9.81 at sea level. This measurement refines the altimetric conversion grid and , ultimately, the calculation of Mont Blanc’s altitude.
Leica Geosystems, a long-standing partner.
A partner since 2001, Leica has kept pace with all technological developments across the 15 measurement campaigns. In 2026, Leica and the Hexagon Group supplied the instruments, including the ground-penetrating radar, and produced the 3D model of the bedrock.
Sogelink : from the terrain to the 3D model.
Sogelink supported the drone-based photogrammetry. Its software enabled the 1,300 images and field surveys to be transformed into usable data, as well as 3D representations and point clouds of the summit.
Géofoncier: data accessible to all.
The land surveyors’ land information portal makes its mapping data available to the expedition, enabling the sharing of all documents resulting from the survey.

Why keep going up?

Une mesure seule ne dit pas grand-chose. Ce qui a de la valeur, c’est la série : vingt-cinq ans de relevés réalisés avec la même rigueur, qui constituent la mémoire du sommet. Sa hauteur, son déplacement le long de la crête, et désormais la forme du rocher qu’il recouvre.

Car au sommet, rien n’est simple à interpréter. Dans le livre « Mont-Blanc, mesures d’un mythe » (éditions Esope, 2021), publié pour les 20 ans de la mesure, le météorologue Yan Giezendanner le soulignait prudemment :

« Nous sommes très haut au niveau du sommet du mont Blanc, à mi-hauteur de la troposphère. Or si les effets des variations du climat sont sensibles à très basse altitude, on ne relève pas de réchauffements dans la partie supérieure de la troposphère. »
Yan Giezendanner, météorologue, dans « Mont-Blanc, mesures d’un mythe » (Esope, 2021)

Dans le même ouvrage, le glaciologue chamoniard Luc Moreau voyait dans le sommet un témoin unique :

« Le sommet du mont Blanc est l’endroit le plus haut et sera le refuge de la dernière glace en cas de poursuite du réchauffement. C’est un glacier froid, le plus froid de France : si tous les glaciers fondent, il sera le dernier à rester en place. 20 années de mesures, c’est trop court, et nous disposons de trop peu d’informations sur tout ce qui se passe à près de 5 000 mètres.

Nul ne sait aujourd’hui si le réchauffement climatique affecte ou non l’altitude du mont Blanc. »
Luc Moreau, glaciologue, dans « Mont-Blanc, mesures d’un mythe » (Esope, 2021)

Les Géomètres-Experts mesurent, la suite…

Cinq ans plus tard, la série couvre vingt-cinq années de mesures et quinze campagnes, et elle regarde désormais sous la glace. C’est tout le sens de cette aventure. Les Géomètres-Experts mesurent, avec précision et dans la durée. Aux glaciologues, climatologues et spécialistes d’interpréter. Et à chaque nouvelle campagne, en partageant les données et en confrontant les méthodes avec les autres équipes, la mémoire du sommet s’enrichit.

Pour TERIA, le mont Blanc s’inscrit dans notre démarche de société à mission engagée depuis 2021 : apporter la précision centimétrique là où elle sert la connaissance, de la Barre des Écrins au glacier d’Arcouzan, du Manaslu à l’Antarctique.

Le sommet est atteint par chacun. La mesure, elle, est collective.

French Expert Surveyors: Mathieu Dagron (Chair of the Mont Blanc Commission), Jean des Garets (Chair of the Haute-Savoie Departmental Chamber), Paul Maisse, Christine Befre, Jean Cassassoles, Wilfried Maduli, Christophe Gillot, Guillaume Tuquoi, François Hulot (student).
Technical partners: Farès Mahi (TERIA), Farouk Kadded, Raphaël Goudard and Nicolas Reviron (Leica Geosystems), Aurélien Dalmas (Sogelink), Cyril Dugard and Teikiheetini Paperin (Géofoncier), Alexandre Tisserant, Renaud Dugoy and Victor Rudant (IGN).
High-mountain guides: Serge Bazin, Laurent Simoni, Julia Virat, Lucas Bernardin, Olivier Balardi, Yann Winterberger, Gilles Baudry, Nicolas Vogel, Jacques Senly.
Images: Pascal Tournaire (photographer), Bruno Peyronnet (director), Bertrand Delapierre (director of photography).