Technical

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       - Skiing on Glaciers -               

Glaciers, those rivers of ice that wend their way so majestically through the high mountains, are formed by the accumulation of snow at high altitudes. Permanent snowfields are created when layer upon layer of snow build up faster than the rate at which they are melted by the sun and the weather. Compacted by the weight of additional snowfalls, the snow gradually turns to dense ice. There are three distinct layers in an established glacier: the top layer of snow on which we love to ski, a compressed snow/ice layer in which crevasses can form ready to trap the unwary and, below that, a dense ‘plastic’ layer of ice. 

Under the pull of gravity, glaciers slowly flow downhill. The Mer de Glace above Chamonix, typical of many Alpine glaciers, moves at approximately 10metres per year. This flow rate is far from constant and varies considerably throughout the glacier. Drag between the ice and bedrock slows the rate of flow at the sides and speeds it up at the centre, giving rise to the classic ‘C’ pattern on the surface of many glaciers. This differential flow rate is the main cause of crevasses. When the stresses within the ice are greater than its strength, cracks appear and crevasses are formed. There are two main types of crevasse: the ‘transverse’ crevasse across the main flow occurs where the ground steepens (convex) and the ‘longitudinal’ crevasse where the glacier widens. Any crevasse, though, can be a hazard to both mountaineer and skier. 

Glaciers are often described as either ‘wet’ or ‘dry’. By mid summer the surface snow in places will have melted away, exposing the ice beneath, sometimes running with melt water - this is a ‘dry’ glacier! In late winter and at spring time when ski mountaineers are likely to be on the move, the glaciers will (if you are lucky) have a thick blanket of snow and be described as ‘wet’.

Glaciers do pose a real threat to anyone venturing onto them. Indeed I have two friends who, thankfully unharmed, have been rescued from what could have been an icy tomb.

Although glaciers and crevasses constantly move, their general location and extent do not. Maps will show the safest routes and highlight difficult areas. Guide books and local knowledge can also prove invaluable. Other skiers’ tracks may indicate a good line.

Careful observation of the snow surface will often reveal the whereabouts of a crevasse. Look for depressions or dark shading in the snow.

Avoid shock loading the snow. You may unknowingly be crossing over a crevasse. Ski lightly and avoid heavy jump turns if possible.

It is essential when skiing in crevassed areas not to fall over. If you can’t ski steadily in a controlled manner, go and ski somewhere else.

If someone does fall, however, don’t all rush to help and always avoid congregating in one area thus overloading the snow.

Skis spread load and make good snow shoes. Adopt the habit of always keeping at least one of them on (eg. when fitting skins).

When crossing crevasse lines do so at right angles. Remain spaced from companions to minimise loadings and to avoid the chance of more than one person breaking through the snow.

When conditions dictate, the party should rope together.

Above all, always treat glaciers with respect.                

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