Mountain guide

Chamonix-Mont-Blanc, France

Mountain guide

Chamonix-Mont-Blanc, France

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Montagnat M.,CNRS Laboratory for Glaciology and Environmental Geophysics | Weiss J.,CNRS Laboratory for Glaciology and Environmental Geophysics | Cinquin-Lapierre B.,CNRS Laboratory for Glaciology and Environmental Geophysics | Labory P.A.,CNRS Laboratory for Glaciology and Environmental Geophysics | And 3 more authors.
Journal of Glaciology | Year: 2010

For the first time, to our knowledge, a scientific study of the formation and evolution of waterfall ice, the ephemeral ice structures that form from the freezing of liquid water seeping on steep rock, was performed. We surveyed and analysed three waterfall ice structures near Glacier d'Argentière, Mont Blanc massif, France, between winter 2007 and spring 2009. We reconstruct the global evolution of two vertical ice structures using automatic digital cameras, while the internal ice microstructure was analysed using ice coring and sampling. Macro-and microstructural observations are considered, along with temperature conditions recorded at a nearby meteorological station and directly within the ice structure. They reveal that vertical structures initially grow rapidly from the aggregation of stalactites with microstructures indicative of temperature conditions during their crystallization. After this initial stage, the volume of the ice structure reaches an asymptotic value, as water continues to flow inside the structure, isolated from the outside cold ice; the outer surface remains dry. At the end of the season, the collapse of the free-standing structure does not occur by progressive melting, but is initiated by a horizontal crack propagation at the top. The initiation of this crack seems to be triggered by a drastic temperature decrease.


Weiss J.,CNRS Laboratory for Glaciology and Environmental Geophysics | Montagnat M.,CNRS Laboratory for Glaciology and Environmental Geophysics | Cinquin-Lapierre B.,CNRS Laboratory for Glaciology and Environmental Geophysics | Labory P.A.,CNRS Laboratory for Glaciology and Environmental Geophysics | And 3 more authors.
Journal of Glaciology | Year: 2011

We present a study of the mechanical (in)stability of the ephemeral waterfall ice structures that form from the freezing of liquid water seeping on steep rock. Three vertical structures were studied, two near Glacier d'Argentière France, and one in the Valsavarenche valley, northern Italy. The generation of internal stresses in the ice structure in relation to air- and ice-temperature conditions is analyzed from pressure sensor records. Their role in the mechanical instability of the structures is discussed from a photographic survey of these structures. The main result is that dramatic air cooling (several °Ch-1 over several hours) and low temperatures (<-108°C), generating tensile stresses and brittleness, can trigger a spontaneous or climber-induced mechanical collapse, leading to unfavorable climbing conditions. Ice internal pressure fluctuations are also associated with episodes of marked diurnal air-temperature cycle, with mild days (few °C above 0°C) and cool nights (few °C below 0°C), through the occurrence of water ↔ ice phase transitions within the structure. These ice internal stress fluctuations seem, however, to have a local influence, are associated with warm (near 0°C), wet and therefore particularly soft ice and do not trigger a collapse of the structure.

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