Mountain flying on skis
Crevasse
risks
How crevasses close up at the start of the season
The process of crevasses closing up is illustrated by 3 photos of the Girose glacier, where we land.
The glacier itself is made of ice (as the name suggests!), which has no elasticity. The glacier “opens up” at the obstacles and breaks of slope it meets as it “flows” down the valley. These are the crevasses we can see in summer, once all the snow of the previous winter has melted. Autumn snowfall then covers these areas and, through small successive accumulations, snow “bridges” close the crevasses. This process is slow and depends on the size of the crevasse. In December they are still clearly visible (1): landing is strictly impossible. Early in the season the snow bridges are still fragile, and consolidation by refreezing also happens very slowly (2). That is why it is sensible to wait until early January (and even then!) for our first landings, even if we are all impatient!! In photo 3 the crevasses have almost disappeared. Conditions become ideal from early February to the end of April, and then, once again, the greatest caution is needed in May…
On 2 January, the snow layer starts to fill the crevasses. The danger is still there, but less visible.
On 10 January, the crevasses can hardly be seen any more. The only way to be sure is to have carefully watched how much snow fell between the 2nd and the 10th… or to wait a little longer.
Credit: Eric Vuillermoz and Bernard Moro