” Help ! », exclaims a visitor. In the middle of a staircase at the Aiguille du Midi observatory, 3,800 meters above sea level, a lady out of breath has just suffered a bout of illness. Agents come running: a few minutes of sitting, and things get better. “At this altitude, this happens regularly”recognizes Benjamin Desmargers, the operations manager of the Aiguille du Midi cable car, whose departure is located in the center of Chamonix (Haute-Savoie).
Tourists from all over the world parade there: 550,000 in 2023. It must be said that the arrival station, placed like a space station on a rocky outcrop, offers a breathtaking panorama of the Mont-Blanc range. Summer and winter, between 25 and 50 employees run this site, and every evening, two technicians spend the night at the summit, like lighthouse keepers on the roof of the Alps. “We sleep very poorly at this altitude”, admits one of them. When violent winds prevent them from going back down, they sometimes remain stuck for several days in this landscape of rocks, peaks and cliffs.
If oxygen depletion is a well-known risk associated with high mountains, others are less so. Who knows that the Aiguille du Midi observatory is located, in part, in a permafrost zone? These rocky soils streaked by ice, which freeze then thaw depending on the time of year, are found above 2,500 meters. However, with rising temperatures and the multiplication of heatwave episodes, the “active” layer of permafrost (the one that freezes, then thaws) becomes deeper and deeper. This development can create cracks in a cliff, deform terrain, cause blocks of stone to fall or destabilize the infrastructure present at these altitudes.
“If rock compartments break away upstream of the passage of people, or if foundations start to move, obviously, this represents a danger”, explains Ivan Brunet, general director of Alpes Ingé, a design office specializing in the monitoring of permafrost zones. He follows the Aiguille du Midi and has observed, in fifteen years, “very rapid developments”. The site is highly monitored – and various consolidation works have been undertaken. Rocks, for example, were fixed using large nails to prevent them from cracking. Temperature sensors, crack gauges, cameras and an “automated monitoring” system with alert thresholds have been installed. Added to this is the daily monitoring of the teams.
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