In the light of the vast spaces of the Mont Blanc massif, Tête Rousse is only a very small glacier, barely visible under the snow. At the origin of a deadly disaster in 1892, it is nevertheless one of the most watched in the French Alps.
Located at almost 3200 meters above sea level on the “royal road” leading to the roof of Europe, it measures only a few hundred meters for 65 meters thick and therefore pales in comparison to the majestic giants of the valley. from Chamonix like the Mer de Glace or Argentière.
But Tête Rousse, like neighboring Taconnaz, is part of the “little handful” of glaciers considered potentially dangerous for the populations settled downstream, according to the specialist Christian Vincent.
France has some 550 glaciers (for about 200,000 worldwide) some of which are “to disappear or collapse“due to global warming.
This is not the case for the moment of Tête Rousse, which, “paradoxically“, would conversely be “cool down“Unlike others, it has not even lost much thickness in recent years, underlines Christian Vincent, pointing to the snowy expanse where specialized teams are busy around drilling rigs and pumps.
Tou two glaciologists from the Institute of Environmental Geosciences (IGE) in Grenoble, Christian Vincent and Olivier Gagliardini came on this hot July afternoon to supervise the burial of temperature sensors in the ice.
The process is not easy at this altitude where the devices can suffer from lightning or landslides, underlines Olivier Gagliardini. The glacier, which is only accessible on foot or by helicopter, is close to the infamous Goûter corridor, nicknamed “hall of deatht” for its numerous rockfall victims.
If the glaciers of Taconnaz and Tête Rousse have in common to potentially threaten the valley, they nevertheless represent two completely different scenarios: “Taconnaz is warming and this one is cooling, it seems completely contradictory and yet the origin is the same, it is the warming of the atmosphere“, emphasizes Christian Vincent.
The first is a cold glacier (less than zero degrees) suspended, which has seen its temperature increase and which therefore risks being destabilized in the long term and causing ice avalanches.
The case of Tête Rousse, a glacier both temperate (at zero degrees) in its upper part, and cold in its lower part, is more complex and can be explained by “thermodynamic processs” related to its very slow flow due to its gentle slope and its “lock“.
If the models are confirmed, it could eventually “become completely coldd”, in which case scientists and public authorities could relax their surveillance, which has been constant since the alert was given in 2010.
The Tête Rousse glacier directly overlooks the town of Saint-Gervais-les-Bains, some 2,000 meters below, in particular the Fayet area where the town’s thermal baths are located.
This is where an avalanche of liquid and rock debris caused by the rupture of a large pocket of water in the glacier destroyed everything in its path in 1892, killing around 200 people.
A similar catastrophe was narrowly avoided in 2010 when a new pocket of water of some 55,000 cubic meters was detected within Tête Rousse. Under pressure, this time it threatened some 3,000 people below.
Public authorities, alerted by scientists, organized emergency pumping. But the water table reformed the following year, then in 2012, leading to new and costly oil changes.
Today, the danger is less significant but the glacier, lined with piezometers to measure the pressure, scanned by radar and by magnetic resonance of protons, remains under close surveillance, especially since another cavity has been spotted in its part. high.
“Glaciers are an extremely valuable natural climate indicator, easy to measure and highly visible to public opinion.“, notes Christian Vincent.
However, it is necessary to avoid the “shortcuts“and put everything on the account of global warming, he underlines, recalling that the falls of seracs (blocks of ice) are for example part of the”normal operationl” of a glacier.
Studying them also makes it possible to understand the processes of ice deformation and “skid“glaciers on their bed, providing valuable insights into what might happen in Antarctica in the future.
“There is a phenomenal stake here since it conditions the rise in sea level in the future.“, explains the glaciologist.
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