by Carol Smock

Created on: November 15, 2010

The International Commission on Snow and Ice devised a classification system in 1954, updated in 1985, that allows better understanding of the structure and stability of snow cover. Various groups, from scientists to hikers to skiers to road maintenance engineers and farmers use the system to describe and determine the characteristics of snow cover in a given area.

This is an important function in understanding avalanche safety, seasonal snow cover, snow mechanics, snow hydrology, and the physics of snow. Even the shape of snowflakes can influence the stability of a snow pack and help determine avalanche safety and the ease of road maintenance.

Snow cover usually occurs in layers deposited during successive storms. Each layer will be more or less homogeneous. However, this can change due to wind patterns and events such as snow falling from trees. Ice layers also occur in a snow pack. These are either vertical channels, horizontal layers, or basal ice.

Snow is very porous, being composed of ice and air and, sometimes, liquid water. The characteristics of a mass of snow are determined by its temperature, its texture, and the proportion of ice, water and air present.

Density, or the weight of a particular volume of snow, is an important consideration, along with the wetness of the snow mass. Other factors are strength, strain or stress on the snow mass, hardness, temperature, and layer thickness. Load bearing capacity is an important consideration for hikers and skiers.

A coarse, grainy type of snow called depth hoar is often responsible for avalanche. This type of snow tends to occur early in the season. Because of the slippery nature of the grain, the layer of snowfall does not bond well to subsequent layers. With the weight of later snowfalls, the bond may fail and cause an avalanche.

To accurately predict the danger of avalanche, it is necessary to carefully record the depth and condition of each layer that makes up a mass of snow. The temperature, wind conditions, steepness of snow, wind direction, and weight of new layers of snow are other factors involved in predicting an avalanche.

Cracks shooting across the surface of a snow pack or small slabs shearing off are signs that a snow mass is weakening. Also significant would be the “whump” or hollow sound that a weak layer makes when someone walks across the surface.

In addition to the other qualities of snow, the international commission has produced a classification system for crystals

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