Drilling in the Vallée Blanche : that was 50 years ago

People are active this June 1971 at the glaciology laboratory in Grenoble, in the cramped square at 2 rue Très Cloîtres in the old bishopric, right next to the Cathedral. The brand new ice core drill is ready and the drilling equipment, the generator set and the elements of the hut are assembled to be transported to Chamonix. The team of 7 to 8 people set off for a drilling operation on the Vallée Blanche plateau above an altitude of 3600 m with a prototype of a homemade "thermal" drill. Its principle : a 3.8 kW heating element at the end of a 3m tube cuts a crown of ice and sinks into the ice. The ice cylinder (the core) enters the tube and during ascent, extractors (stops) break the core at its base and hold it in the tube. The expected ice cores will document the functioning of the glacier. This operation is a life-size test for the equipment, and a baptism of fire for some young PhD students who take part in this mission.
The mission is scheduled for two weeks, but we know that it will have to deal with the unforeseen events of a prototype, and the contingencies of high mountain meteorology during this period.
The Cosmiques refuge built entirely in wood in the 1950s to house a cosmic ray detector (bubble chamber) will be used for a time by Louis Leprince Ringuet. For now, it will serve as a backstop for the team’s accommodation. It is a refuge guarded by Rolland Ribola and welcomes high mountain guides and their clients, international big names and seasoned mountaineers. It must be said that the refuge is on the route of the great races to the Mt Blanc and a fantastic panorama is offered : with the south face of the Cosmiques, the Verte, the Grandes Jorasses, the Dent du Géant, the Glacier du Géant, the Pointe Helbronner ...
The 1,500 kilos of equipment are transported to Chamonix and then taken to L’Aiguille du midi by the cable car mobilized for the occasion. Via the Aiguille tunnels, at the end of a narrow snow-covered platform, you reach the service bucket inclined at 30° on the slope which joins the rock just downstream from the refuge. From there, the equipment is loaded onto a tray pulled with a capricious skidoo, if not by force of the wrist, to the place of drilling located in the middle of the tray. The routing of the drilling mast in 2 pieces of 4m, oversized for the cable car cabin of the second section, was a delicate operation. We tie it to the roof of the cabin and Ribola, the local expert insensitive to vertigo, watches everything, standing by holding on to the cables ...
Very quickly the drilling begins on July 7 and after having crossed the 30m of porous snow layer, the drill takes its cruising speed. The 1.5m ice cores are extracted on each round trip of the drill and one recognizes the successive summer and winter layers allowing a rough dating. No less than 5m of snow falls per year, which is the water equivalent of 3.10m, or more than twice the rainfall in the valley. The labeled ice cores are packed in insulated boxes and sent as soon as possible to the cold room in Chamonix then that in Grenoble. On July 18, the heating element of the core barrel collided with the rock at 180.5 m, that’s it, we reached the bottom of the glacier ! A pebble is even trapped in the last ice core !
The hole filled with water from the melting snow on the surface. This water creates a few short circuits in the quickly repaired drill. With water, the glacier at depth is at zero degrees (the glacier is said to be "temperate") and the 1 to 3% of water it contains promotes its sliding at its base. In contrast, at high altitudes, the summer melting is not sufficient and the temperature of the glacier is negative : the glacier is said to be "cold" and it is frozen to the rock. Today, with global warming and extreme events favoring the melting of snow at high altitudes, there is good reason for concern about the stability of cold perched glaciers that can set off in devastating avalanches.
With this mission, the ice core dril built by Daniel Donnou, a "geo-find-everything" technician under the leadership of François Gillet, engineer, "wins his ticket" for other horizons. In mid-July, Claude Lorius, who is already involved in snow studies in Antarctica, has just joined Louis Lliboutry’s laboratory in Grenoble with his team of researchers and technicians. Lorius goes there accompanied by Marcel Renard of the French polar expeditions Paul Emile Victor. In Antarctica, just like in Greenland, the ice thickness reaches over 3000 m and the glaciers are of the "cold" type : the layers of snow accumulate almost infinitely and one can go back very far in time. In addition, since there is no leaching, the snow layers retain their physical properties, chemical content and other isotopic composition (an indicator of the temperature at which the snow has formed). Moreover, the drilling of Camp Century (1300m) in Greenland, which the Dane Willy Dansgaard has just analyzed, dates back to the last ice age and spanned nearly 80,000 years. The same is expected with the Byrd drilling in Antarctica (2138m) drilled in 1969.
The Antarctic Treaty signed in 1961 froze the territorial claims of Nations and it encourages international collaboration. The International Antarctic Glaciology Project (IAGP) was launched in 1969 and brought together the United States, the Soviet Union, Australia, Great Britain and France with the objective of exploring part of East Antarctica which includes among others the Adélie Land and the stations of Vostok (USSR) and South Pole (USA). Radar soundings reveal a thickness of more than 3000 m at Dome C, or even 3700 m at Vostok. The ice sheets in the polar caps are great natural archives for studies of glaciology and paleoclimatology : drilling in central regions then becomes one of the major objectives of this research. At the same time, techniques for analyzing polar ice are improving all over the world with mass spectrometry, physical measurements and chemistry allowing the detection of volcanic eruptions which, along with measurements of very low level radioactivity, contribute to date the ice.
The Donnou drill is therefore sent to Dumont D’Urville in Adélie Land at the end of 1971. The drilling will not exceed a depth of 30m : the glacier is at -20 ° C and everything is freezing, but the team returns to Grenoble enthusiastic and, again, full of new ideas. Two years later, the team returned to Terre Adélie with a new version that reached the bedrock at a depth of 305 m. The road to Dome C is then open. With the support of the planes of the American NSF within the framework of the IAGP project led by Lorius, the team of Donnou will carry out a drilling of 905m at Dome C in 1978. The ice core describes the climate of the last 30,000 years, covering the last glacial maximum which peaked 18,000 years ago.
In 1980, Robert Delmas and his two PhD students in chemistry : Jean Marc Ascencio and Michel Legrand, developed the technique for measuring the CO2 contained in air bubbles, a sample of past atmosphere trapped in ice. In the Dome C cores deposited during the Ice Age, the CO2 content appears 50% lower than that formed in the warm period that follows, thus demonstrating the modification of the carbon cycle with the climate. Antarctic ice will later reveal the importance of CO2 through its associated greenhouse effect in past climate changes. If our human activities continue to emit massive amounts of CO2 (37% of additional CO2 in the atmosphere in 2020 compared to 1850) global warming of the earth can only be inevitable.
Since then, other ice core drills have emerged with major international drilling projects for studies of past climates. The relationship between greenhouse gases and climate has been extended to other gases (methane) and other chemical elements (aerosols) of the past atmosphere with records that are references : Vostok over 150,000 years (in 1987) then over 400.00 years (in 1999) and to date over 800,000 years with the Epica core (drilled at Dome C). With the European "Beyond Epica" project underway at the Franco-Italian Concordia station in Antarctica, the international scientific community is hoping for a recording that will span 1.2 million years !

Author : J.R. Petit - 09/07/2021
Original article