An expedition made up of expert surveyors is taking measurements this week to find out the exact height of the highest mountain in the Alps.
It became a habit. Since 2001, expert surveyors have launched an attack on Mont-Blanc approximately every two years to verify the precise altitude of its summit.
President of the commission in charge of this 12th measurement of the highest mountain in the Alps, Denis Borrel will be part of the expedition which leaves this Thursday for four days. With him, no less than fourteen participants – specialists as well as technical partners – and seven guides.
“We will arrive at the summit on Friday. Then, we will take between half an hour and three hours, depending on the weather conditions, to carry out different measurements,” explains this seasoned mountaineer, trained and acclimatized in recent days around 4,000 meters to “ make red blood cells and cope with the lack of oxygen.
Find the exact vertex point
To know the size of Mont-Blanc, you must first find its highest point, the summit ridge being almost at the same horizontal level over a hundred meters long.
“We walk around this area by pointing a GPS attached to a cane as close as possible to the ground. Thanks to a tablet giving us the altitude under our antenna, we determine the exact summit,” summarizes this expert surveyor from Haute -Savoy.
Once the right location is identified, the rod holding the GPS is pushed into it. “We obtain altitude corrections in real time via other GPS devices, static and anchored in the valley, which send their signals via the internet and satellites.”
But the value is still only approximate at this time, until the National Institute of Geographic Information (IGN) makes tiny revisions to the height.
“From the measurement carried out on Friday, the IGN must subsequently refine the calculation taking into account the actual zero level below this point,” explains Denis Borrel. “Concretely, this zero altitude differs slightly from sea level under rock masses, such as mountains, due to the Earth’s magnetic field.”
In light of this parameter, the new official size could thus be announced on October 5 during a press conference.
A 3D model of the summit
In 2021, the giant of the Alps stood at exactly 4807.81 meters, or 92 centimeters less than previous readings. “A natural phenomenon” according to Denis Borrel, who refutes the idea that we can attribute this decline to the effects of global warming:
“It all depends on the influence of the wind, which shapes the summit depending on which side it blows. Scientists have drawn no conclusions and consider that the top of Mont Blanc is a fridge, with no significant melting observed.”
To ensure this, the expedition must nevertheless carry out other data collection. A so-called “kinematic” GPS is provided to map the different points of the summit snow cap. “The idea is to calculate the volume of snow and ice compared to previous years to see if there is a correlation between a possible rise or descent of Mont-Blanc,” continues the expert.
If the weather is not too unpredictable, a drone – for which the small troop had to request prefectural authorizations – must then scan the area and take several photos using a photogrammetry system.
“Put end to end, these photos will give us a 3D model of the summit using billions of points listed in around fifteen minutes,” explains Denis Borrel.
Representations useful to the scientific world likely to be exploited by glaciologists or climatologists, capable of observing whether or not the roof of Western Europe is also suffering the full brunt of climate change.
Source: BFM TV