Image © 2009 Institut Géographique National, France. Summer satellite image of the Argentière frozen waterfall area (45★8′ N, 6★8′ E).
FROZEN WATERFALL PROFESSIONAL
However, we hope that the observations reported here, when properly summarized for a non-scientific audience, will ultimately help climbers and professional guides to improve their evaluation of field conditions.Īs the literature on this subject is nearly non-existent, our aim is to provide initial observations and analyses that could serve as a basis for future work. In this paper, we focus on ice formation, internal microstructure and evolution with weather conditions: How fast does a frozen waterfall form in relation to air temperature? What can we learn about the growth mechanism from an analysis of ice microstructure? Does this mechanism depend on the orientation of the waterfall, on its steepness? At this stage, our goal is of a fundamental nature rather than to evaluate objective risks, even less to build a scale of risk in a way similar to that developed for snow avalanches ( Reference AnceyAncey, 1996). Our subject is a famous ice-climbing site near the icefall of Glacier d’Argentière, in the Mont Blanc massif. Beginning in the 2006/07 winter, we have performed a case study of waterfall ice formation, structure, evolution and mechanical stability. To our knowledge, with the exception of one internal report ( Reference BianchiBianchi, 2004), there is no scientific study of waterfall ice in the literature. Among these, subjective risks were the main cause, but ice-block falls and collapse of the structure caused 14% and 5.5% of the accidents respectively. 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.
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).
Nowadays, waterfall ice climbing is a fully developed winter alpine activity: in France the number of ice climbers, regular or occasional, can be roughly estimated from the number of ice axes sold, ∼10 000. This activity appeared a few years later in the Alps and developed rapidly in the 1980s–90s. In the early 1970s, some climbers, particularly in North America, started to climb in winter on ephemeral ice structures formed from the freezing of liquid water seeping on steep rock, i.e. on ice formed essentially from the densification of snow. Until the 1970s, ice and snow climbing was largely restricted to the summer season on glaciers and perennial snow/ice couloirs or gullies, i.e. This understanding helps to guarantee the security of alpinists and is generally included as a part of mountain guide education and training. Today, glacier structure, dynamics and evolution are better understood. This helped to overcome the fear previously associated with high altitudes and with glaciers. 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). In the early days of alpinism at the end of the 18th century, activity was intimately associated with scientific exploration.
FROZEN WATERFALL CRACK
The initiation of this crack seems to be triggered by a drastic temperature decrease. 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. 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. They reveal that vertical structures initially grow rapidly from the aggregation of stalactites with microstructures indicative of temperature conditions during their crystallization. Macro- and microstructural observations are considered, along with temperature conditions recorded at a nearby meteorological station and directly within the ice structure. 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. We surveyed and analysed three waterfall ice structures near Glacier d’Argentière, Mont Blanc massif, France, between winter 2007 and spring 2009. 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.