Snow structure

Appendices: [ Instructor 1 course outline | Instructor 2 course outline | Instructor 3 course outline | APSI Nordic rules and regulations | equipment size charts | snow structure | waxing tips ]

The basics of snow

To spend all one's time teaching skiing and knowing nothing about the medium on which you work is akin to sailing without understanding winds, waves, or currents. Whilst some may argue that it is quite possible to teach skiing without even the faintest inkling of what snow really is and really does, no instructor could deny that snow does affect the performance of the individual skier, such as when we have too much snow, too little snow, too icy snow, too soft snow, too fast snow, too slow...

An understanding of snow is practically essential if one is to understand waxing enough to achieve desirable results, and the ability to pass on this information to others is equally desirable in any instructor. Luckily, unlike when instructing in many other countries, we do not need to understand snow in order to avoid potential avalanches, although there are places in Australia where this knowledge is extremely desirable (deaths related to avalanches have occurred locally).

Snow will fall in Australia invariably around 0°C, whereas it is more normal in colder climates for it to fall in below-freezing temperatures. Likewise, whereas in other, colder countries, snow will remain in the state that it has fallen (usually fine-grained, or new snow) for many days if not weeks, often until the next snowfall, it is highly unusual in our climate for the snowfall to remain in its 'virgin' state for very long at all - the time scale is often in hours and sometimes days, rather than days or weeks.

The coldest recorded temperature ever recorded in the Australian snowfields was -22.5°C at Kiandra on the 19th of June 1916. Due to the recent onslaught of the greenhouse effect, this record is likely to stay in the record books for some time.

These days, it is unusual for the nighttime temperature to drop below -10°C, and during the day, even in mid-winter, the temperature usually doesn't drop much below -5°C. In fact, during the day the temperature is quite likely going to climb above the freezing point, except on overcast or cloudy days.

Consequently, Australian snow will undergo many changes (metamorphoses) in its life-cycle, unlike those fortunate snow crystals that land in the Antarctic (on a rare windless day), or Northern Europe. It is these changes that interest the skier, and especially the skier that wants to get maximum performance, and minimum effort, from her/his skis.

Newly-fallen snow

For the purposes of waxing, snow can be categorised according to its age, and its subjection to temperature and weather. Newly-fallen snow looks somewhat like the traditional crystals that one sees on postcards, or in reference books. It is not uncommon to see this type of snow in Australia falling in large 'clumps', and remaining in that form on the ground for some time after a snowfall. However, the water content of Australian snow tends to be much higher than that of other, colder climates, and because of this the crystals tend to be a little more misshapen than their foreign cousins.

Looking at the substance under a microscope will reveal that freshly-fallen snow maintains its crystal structure for a long time, providing that the temperature remains below freezing or if the wind does not pick up and deposit the crystals elsewhere, thereby breaking the arms, or dendrites, of the crystal.

Most newly-fallen snow is ideal for skiing on, since there is a good deal of air mixed in with the mass, the snow will compact easily and provide a smooth base for skiing on. Because the snow itself is so smooth when compacted, it has very little effect on the wear of either skis or ski waxes, and therefore proves to be ideal for the use of grip waxes and hard glide waxes.

Uncompacted newly-fallen snow that is mostly air is termed powder snow - and is rarely seen in Australia. It is far more common in the Rockies, or on the north island of Japan, or in northern Europe. Whilst powder snow is an absolute delight to ski downhill through, it is quite the opposite sensation when attempting to diagonal stride, or worse, climb uphill. A short journey of 400 metres can take all morning if it involves a 40 metre climb!

The last fall of real powder snow fell in Australia in 1803, and only lasted for a few minutes as the moisture content of the snow was high, and became higher as the warm air and sun melted the upper surface. Wet powder snow (which, technically speaking, should not really exist) is worth avoiding like the plague, either when climbing, or descending.

Settled snow

After some time, freshly-fallen snow will begin to erode, through the action of wind, or pressure from above (as in a skier skiing over the top and compacting it, or through further snowfalls), or through sublimation. Without wishing to get too technical at this stage, sublimation is the process of the transportation of water molecules around a snow crystal, due to the inherent thermodynamic instability of the crystal structure. This occurs both above and below freezing temperature, although it is much less noticeable below freezing.

The following diagram indicates the day-by-day, or in warmer conditions, the hour-by-hour (or as so often occurs in Australia, minute-by-minute...), changes that a snow crystal will experience, regardless of temperature, due to sublimation:

Sublimation of a snowflake in four stages. The time scale can be anything from minutes to weeks or longer.

In these conditions, snow tends to exhibit different properties to that of freshly-fallen snow, and becomes more dense and often more humid (or even very wet). Thus the wax that skiers might use would tend to be softer than that of freshly-fallen snow, even though the temperature alone may indicate a harder wax. The density of the snow creates a wear problem for skis, and grip waxes need to be applied more often, or over binder waxes.

Coarse-grained snow

Coarse-grained snow is most common in Australia right throughout winter. It is fallen snow that has been through a cycle of partial melting and refreezing one or many times. The process of sublimation will have transformed the crystals into round globs of ice (on a macro level), which, depending upon the part of the cycle they happen to be in, will produce excellent conditions for skiing, or difficult conditions. Water is present in the snow in large quantities, and the humidity of the snow structure will be almost 100%.

Non-wax skis become helpless when coarse-grained snow freezes, and it is not uncommon to experience severe wear problems of the ski base in these conditions. Glide waxes also wear quickly, and will need to be supported by a binder wax.

If the snow-surface has risen to an above freezing temperature, the snow becomes softer (non-wax skis will obtain grip again) and, depending upon the level of thawing experienced in the snow-pack, will be either extremely supportive to the weight of a skier, or extremely slushy and difficult to move about in. Either way, to obtain grip on these surfaces, knowledgeable skiers resort to klisters, which are ideal in these conditions.

Although some klisters are colour-coded by temperature, temperature plays less of an important role when deciding upon a choice of klister, rather it is the humidity and coarseness of the snow crystals that become more important.