Progression sur neige et glace / Progression on snow and ice
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écrit par Wladimir T.

chef de course et instructeur au Club Alpin Suisse

Le 3 avril 2013

Progression sur neige et glace

vous avez dit équilibre ?

Dans le rocher, le fait de pouvoir saisir avec les mains une bonne prise et ensuite y poser le pied donne une impression de sécurité et engendre la confiance.

Sur la neige et sur la glace, en revanche, on ne s’accroche à rien. C’est pourquoi, encore plus que dans le rocher, il importe d’acquérir un très bon sens de l’équilibre.

Quelle que soit l’inclinaison de la pente, le corps doit rester vertical, bien d’aplomb sur les pieds.

Dès le début de l’apprentissage de la technique, il faut, à l’évidence, utiliser le piolet qui constitue le troisième point d’appui.

Cependant, après que chaque nouveau mouvement ait été étudié, Gaston Rébuffat conseille de refaire le même mouvement sans l’aide du piolet, et il ajoute:

« …ainsi, par voie de conséquence, il (le montagnard) aura automatiquement le corps vertical, d’aplomb, ses crampons mordront bien, et surtout il prendra conscience de son équilibre en se rendant compte qu’il tient – et plus d’une fois il en sera lui-même surpris – pourquoi il tient et dans quelle mesure; inversement il réalisera que si son centre de gravité venait à passer à l’extérieur de sa base, c’est-à-dire de ses pieds, il serait en perte d’équilibre, et tomberait. »

Le même conseil est prodigué concernant les crampons. Bien que ceux-ci soient un élément de sécurité, au même titre que le piolet, le débutant devrait s’entraîner à progresser sans crampons en tapant simplement du pied sur des pentes de neige allant jusqu’à 40 degrés et en taillant des marches sur des pentes de glace raides.

« …il y gagnerait beaucoup en connaissance de son équilibre et accroîtrait sa sûreté et son aisance lorsque, par la suite, il devra traverser sans crampons un couloir de neige ou de glace pour, par exemple, poursuivre une escalade rocheuse. »

La technique de progression va tout naturellement dépendre de la qualité de la neige ou de la glace, et de l’inclinaison de la pente.

Qualité de la neige et de la glace

Selon la consistance, on peut distinguer quatre types de neige et deux types de glace.

Neiges molles

Elles comprennent la neige fraîche poudreuse, la neige fraîche humide, la neige     soufflée et pâteuse apportée par le vent et en partie transformée,      ainsi que la neige pourrie.

Neiges cassantes

Aussi appelées neiges croûtées, c’est de la neige molle recouverte d’une croûte dure plus ou moins épaisse qui casse sous le poids du grimpeur.

Neiges dures

Neiges consistantes et stables qui permettent de progresser sans crampons – il suffit de taper avec le bout du soulier pour créer une marche suffisamment profonde pour assurer une progression rapide et sûre.

Neiges glacées

Sur ces neiges la semelle ne mord pas, ou à peine. Le grimpeur doit obligatoirement tailler des marches ou utiliser les crampons.

Glaces granuleuses

Ce sont des types de glaces que l’on rencontre à la surface des glaciers non recouverts de neige ou sur les pentes biens exposées au soleil. Elles sont assez tendres mais nécessitent quand même la taille des marches ou l’utilisation des crampons.

Glaces dures

Ce sont des glaces que l’on rencontre souvent dans les couloirs. Elles sont généralement très dures, d’un aspect vitreux. Ce sont des glaces très difficiles à travailler.

Inclinaison de la pente

Les pentes faibles ont jusqu’à 25 degrés d’inclinaison, les pentes moyennes vont de 25 à 40 degrés, les pentes fortes de 40 à 50 degrés et les pentes très fortes se dressent au-dessus de 50 degrés.

Ces chiffres, toutefois ne sont qu’une indication, car la qualité importe plus que la raideur. Il est préférable d’escalader un mur de neige dure de 45 degrés en bonne condition qu’une pente de 35 degrés en neige instable.

Pour information, la pente moyenne des grandes faces de neige et de glace des Alpes varie entre 45 et 55 degrés.

Progression on snow and ice

did you say balance?

On rock, being able to grasp a good hold with your hands and then place your foot on it gives an impression of security and engenders confidence.

On snow and ice, on the other hand, you can’t hold on to anything. That’s why, even more than on rock, it’s important to have a very good sense of balance.

No matter how steep the slope, your body should remain upright, plumb on your feet.

Right from the start of learning the technique, you obviously need to use the ice axe, which is the third point of support.

However, after each new movement has been studied, Gaston Rébuffat advises repeating the same movement without the aid of the ice axe, and adds:

« …so, as a result, he (the mountaineer) will automatically have his body vertical, plumb, his crampons will bite well, and above all he will become aware of his balance by realising that he is holding on – and more than once he himself will be surprised – why he is holding on and to what extent; conversely he will realise that if his centre of gravity were to move outside his base, i.e. his feet, he would lose his balance and fall. »

The same advice applies to crampons. Although crampons are just as much a safety feature as ice axes, beginners should practise progressing without crampons by simply tapping their feet on snow slopes of up to 40 degrees and carving steps on steep ice slopes.

« …they will gain a much better understanding of their balance and will be safer and more at ease when they later have to cross a snow or ice corridor without crampons, for example to continue a rock climb ».

How you progress will naturally depend on the quality of the snow or ice and the steepness of the slope.

Snow and ice quality

Depending on its consistency, there are four types of snow and two types of ice.

Soft snow

They include fresh powder snow, fresh wet snow, blown and pasty snow brought in by the wind and partly transformed, as well as rotten snow.

Brittle snow

Also known as crusty snow, this is soft snow covered with a hard crust of varying thickness that breaks under the weight of the climber.

Hard snow

Consistent, stable snow that allows you to progress without crampons – simply tap the toe of your shoe to create a step deep enough to ensure fast, safe progress.

Frozen snow

In this kind of snow, the sole has little or no bite. Climbers must cut steps or use crampons.

Crumbly ice

This type of ice is found on the surface of glaciers that are not covered in snow or on slopes that are well exposed to the sun. They are fairly soft but still require the use of crampons or steps.

Hard ice

This type of ice is often found in corridors. They are generally very hard, with a vitreous appearance. It is very difficult to work with.

Slope inclination

Gentle slopes are up to 25 degrees, medium slopes are 25 to 40 degrees, steep slopes are 40 to 50 degrees and very steep slopes are over 50 degrees.

These figures, however, are only an indication, as quality is more important than steepness. It’s better to climb a 45-degree wall of hard snow in good condition than a 35-degree slope in unstable snow.

For information, the average slope of the major snow and ice faces in the Alps varies between 45 and 55 degrees.

Vues : 83

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