Gust of wind

In mountain, the gust of wind is a plate of Neige piled up behind a change of incline sheltered of the wind or in the vicinity of a peak.

Creation of the plates

When there are snow and wind, snow is transported towards the sheltered slopes of the wind (change of incline, vicinity of peak) and piles up there.

A light breeze of about 20 km/h is enough to form in a few hours a beautiful plate of more than 20 centimetres thickness. The wind continuing to blow or increasing the power of its breath, the Plaque of snow can quickly become even more important and dangerous, because puffed up snow acquires particular qualities which quickly make to plate a candidate favourable with the release of a Avalanche.

Location of the plates

Independently of a good knowledge of the places, geographical or natural indices make it possible to fear the presence of gust of wind, like the presence of cornices and wavelets on the slopes exposed to the wind, or an abnormally important deposit of snow on the trees.

The slopes, most favourable with the existence of a plate with snow, potentially dangerous for the man, are those ranging between 25 and 45 degrees, is about 80% of the slopes borrowed by the skiers of excursions out-track or the raquetteurs.

Rupture of the plates

The rupture of the gust of wind can be natural when too many snowfalls fresh accumulate on an older plate, or caused, when several skiers of excursion out-track or even of the raquetteurs, cross a vast gust of wind while following the ones behind the others, thus create a cut in the plate, disuniting the low part of the high part.

In (almost) all the cases, the plate itself is not alone causes some, and it existing also a fragile layer subjacent which could propagate the rupture under the plate. This fragile layer is made of snow with low cohesion, such as for example:

snow with plane faces or out of goblet, known as also white frost of depth,
white frost of surface,
grésil (known as also rolled snow)…

Each year of the hundreds of people let themselves take with this trap which can prove to be mortal for good number of them (several tens of per annum dead in France).

Cause first fatal accident on Mont Blanc

The first fatal accident on the Mont Blanc took place in 1820, during the tenth rise. This forwarding, was reported by Alexandre Dumas which collected of it the account detailed near the guide Marie Coutet survivor of forwarding: the customers were English colonel Anderson and Doctor Hamel, meteorologist of the emperor of Russia. After two nights and a day spent to the Large-Mules, the customers require to go up at the top in spite of an unfavourable weather and the guides do not dare to refuse to them. Equipped progresses in fresh snow which goes up to them to the knees. In fact, following the ones derrières the others, their furrow cuts the gust of wind and they end up starting a Avalanche which carries them. Three of the buried guides could not be found.

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