Avalanches - Loose Snow Avalanches

An avalanche occurs when it snows in the mountains.

Countless snowflakes float to the ground as an accumulation of finely branched crystals and form a light cover of newly fallen snow.

New Becomes Old

With time, the cover of fresh snow is subjected to a transformation or what is called metamorphosis (metamorphóo means to transform in Greek). The delicately branched structures of the snowflakes in the snow cover gradually disintegrate.

  Vanishing of the microstructure.

How Does it Happen?

On the one hand, avalanches happen because the fine branches of the snowflakes melt away during sunshine and freeze again when it gets colder. On the other hand, they happen because of an effect called "sublimation". Sublimation is the direct transition from a solid to a gaseous state. Normally, snowflakes melt first of all. Afterwards, the melted snow evaporates and becomes gaseous. In the case of sublimation, the process of melting is omitted, and water molecules directly evaporate out of the ice surface. Formerly, branched flakes acquire a granular shape because of these processes and the snow cover sets. Light, fresh snow turns to granular old snow.

  Old snow without any microstructure.

Layer on Top of Layer

The first layer of snow sets. Some time or other, it snows again and a new layer of fresh snow is formed, which lies on top of the layer of old snow. Under certain circumstances, it is possible that the new and the old layer will not cling together properly. The strength between two layers of snow is called shearing strength by avalanche experts. Shearing strength means strength against shearing, which stands for breaking away or tearing off. The shearing strength depends on the chemical bonding forces between the snow grains or ice granules, the so-called cohesion, and the friction between them. Added to this is the weight of the snow, which presses the snow cover against the slope.

Nevertheless, It Slides Downhill.....

The more inclined the slope gets, the more gravitational forces drag the snow cover downhill. Consequently, the risk of avalanches increases with the steepness of the mountainside and the amount of snow. It becomes especially dangerous when weak layers with only a few millimetres of thickness occur within the snow cover. At this point, small disturbances like skiers or snowboarders are enough to loosen one or more layers of snow and to start an avalanche.

  Outline of an avalanche.

Avalanches Can Be Incredibly Fast!

The fastest avalanches go up to 80 kilometres per hour. Obviously, it does not really make sense to try to escape an avalanche by running or skiing away.