Marmolada avalanche: how scientists monitor French glaciers

Tons of ice and rocks descending at a speed of 300 kilometers per hour. The partial rupture of the Marmolada glacier (Italian Alps) on Sunday July 3 caused the death of at least seven people, eight others were injured, two of them in serious condition. Finally, there are still a dozen individuals whose disappearance is still worrying so much so that the Italian authorities have decided to continue research on the massif this Tuesday morning, July 5.

A process of abrupt rock failure that remains to be determined

Since the disaster, scientists have been scrutinizing footage shot from a nearby shelter to understand the process. “Specialists speak of a serac fall, namely the breaking of a large block of ice, explains Christian Vincent, Research Engineer at the Institute of Environmental Geosciences (IGE) in Grenoble, medal of money from the CNRS in 2022. This type of phenomenon occurs often but rarely on such a scale.” These hanging glaciers form at high altitude (above 3,300 meters) on a very steep slope and are literally glued to the rocks. Typically, these are cold glaciers, whose temperature is below 0° Celsius.

But with global warming – it was +10°C at the highest point of the massif nicknamed “the queen of the Dolomites” – cold glaciers tend to fall into the category of “temperate glaciers” (with a temperature close to 0°C) a lot more unstable. “Beyond this classification, the phenomenon could be more complex: whatever the type of glaciers, they are not immobile, but crossed by meltwater which evacuates from the surface in a discontinuous flow, continues the specialist in the risks of glacial origin. If the liquid accumulates, then infiltrates in depth creating pockets of water, under the effect of the pressure, the risk of rupture becomes greater: the water acts like a lubricant and the glacier glides over the rocks.”

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In France, the ultra-monitored Alpine massif

Given the relief, the French Alps are therefore not immune to this kind of avalanche. If Christian Vincent does not believe in an immediate risk, he stresses that the drama of the Marmolada is “impossible to anticipate.” On the French side of the mountain range, scientists have been stepping up their efforts for thirty years to monitor the retreat of glaciers linked to climate change, which are losing an average of 1 meter per year – a rate which is accelerating since the ratio is rather 1 .5 meters in the last decade. That of Sarennes, historically monitored since 1924 is thus condemned on the scale of two or three years! And the others ?

“At this rate the glaciers located at less than 3,500 meters above sea level could disappear before 2,100”, specifies the specialist. And until then, some of them are closely monitored by a network of temperature sensors – “On the Taconnaz one alone, we have a dozen located between 4,300 and 3,400 meters above sea level at different depths. Added to this are GPS measurements, seismic and pressure probes to better monitor the slightest fluctuations.

Equally exposed and larger glaciers

Undeniably, between the glaciers of Argentière (it has retreated 850 meters over the last thirty years), the Mer de Glace (4 to 5 meters per year), Gébroulaz and Saint-Sorlin, that of Taconnaz remains the most worrying because it involves millions of cubic meters of ice, on a particularly steep slope (40 degrees) and it is located in the lower part of Chamonix. A whole system of avalanche dikes was thus built that could retain 1.8 million cubic meters! “It’s not just the hanging glaciers (serac fall) but also the risks associated with the lakes that form near the glaciers. When the latter retreat, they leave basins where the water retained by the glaciers accumulates. frail natural dams.These end up breaking, causing sudden emptying (like that of the Blosssons).There may also be the formation of pockets of water inside the glaciers (we speak of intraglacial lakes) which threaten homes and must be closely monitored,” explains Christian Vincent.

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Scientists at IGE Grenoble therefore regularly carry out measurements as well as numerical simulations to better understand flow processes and also assess risks. “Assessing does not mean predicting, reminds the specialist. Gradually the Taconnaz glacier is warming up. It will destabilize again. The question is: will it do it in pieces or in a massive way?”. Before reassuring: “There is no imminent risk of collapse, we remain on time scales of several decades.” Throughout the summer, the glaciologist should still not take many vacations.