Waterfall ice: formation, structure and evolution

M Montagnat,D Lavigne,P.A Labory,B Cinquin-Lapierre,L Moreau,F Damilano,J Weiss

doi:10.3189/002214310791968412

Abstract

AbstractFor 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.

Highlights

In the early days of alpinism at the end of the 18th century, activity was intimately associated with scientific exploration
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
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

Summary

Introduction

In the early days of alpinism at the end of the 18th century, activity was intimately associated with scientific exploration. De Saussure performed barometric measurements at the summit of Mont Blanc, France, in 1786, as well as extensive observations of the nature of glaciers (de Saussure, 1779– 96) This helped to overcome the fear previously associated with high altitudes and with glaciers. Ice climbing can be a risky activity as a result of the climbers’ inaptitude, lack of experience or misjudgement (subjective risks), or due to natural hazards such as snow avalanches, ice-block falls, or collapse of the waterfall structure (objective risks). This is not an anecdotal problem: for example, in France from 2000 to 2006, ice-climbing accidents led to 148 rescue interventions, 47 severe injuries and 22 deaths. Subjective risks were the main cause, but ice-block falls and collapse of the structure caused 14% and 5.5% of the accidents respectively

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Conclusion