Avalanche FAQs

Introduction to Avalanches

An avalanche is a fascinating and naturally occuring phenomenon that is caused by unstable snow conditions. Since it is practically impossible to predict where and when the next avalanche will occur, significant amounts of information such as weather forecasts and avalanche forecasts are provided for the winter sports enthusiasts to aid their understanding of avalanche dangers and potentially prevent one from occuring.

The following avalanche information is not to be accepted as a set of instructions, it is designed merely provide guidance for those who wish to go off piste, and facilitate informed decision-making. It is also worth noting that avalanches are not the only dangers of off-piste: natural obstacles such as crevasses, buried rocks or cliffs are also potential hazards. It is highly recommended that you take a mountain guide whilst venturing into unknown territory.

Are avalanches an 'Act of God'?

Avalanches are not easy to predict. Some avalanche paths are only active once every few hundred years; others are active in almost every storm. However, we can predict avalanches to a certain extent. To quote a well-known professional, Bruce Tremper, "they happen at particular times and in particular places for particular reasons". There are always observable signs of instability before an avalanche happens - recognised all too often after the fact: in 90% of all avalanche accidents, the avalanche trigger is the victim (or someone in the victim's party) and 90% of the time, a slab avalanche is involved.

last updated 8-Feb-2008

Are there more avalanches in Spring?

Spring conditions may be the time of year when there are the most avalanches, but once a regular cycle of melting and freezing sets in, predicting the stability of the snowpack is more evident than during the cold winter months. During the freeze phase, the snowpack is at its strongest. Once free water has seeped into the snowpack, through rain or melting, then it can turn into ice when the temperatures go below freezing - the ice forms a sort of 'skeleton' that holds the snowpack together. Melting during the day and freezing at night is a classic springtime process. In these conditions, after a good freeze at night, the slopes are very stable first thing in the morning. Then, as the sun rises (warming east facing slopes first), the ice skeleton holding the snowpack together melts and the slope eventually becomes much less stable.

In melting and freezing conditions, the snowpack is at its strongest during the freeze phase then at its weakest during the melt phase. In between these phases, the sking conditions can be tremendous as long as people haven't been there too late the day before. Get on the slope as the first few centimetres are beginning to melt and then get off. When melting penetrates more than 5 cm then the slope has started to become unstable and you will start to break through the crust - this alone can lead to injury. Making the right calls in these conditions takes experience - but that is part of the adventure!

last updated 8-Feb-2008

Can I get out of the way of an avalanche?

Dry slab avalanches typically reach a speed of 90-130 km/h within about 5 seconds after they fracture. Avalanches that descend from above kill very few people. Wet avalanches usually travel much more slowly, around 30 km/h.

last updated 8-Feb-2008

Can screaming and yelling start an avalanche?

We really don't think so. However if conditions are that unstable, why would you be screaming and yelling out there in the first place - unless it is for help. In our opinion, an increase in the volume of your individual and collective voices is inversely proportionate to the level of your awareness of potential hazards. Explosives that are used for avalanche control are powerful and it is the shock wave produced by the blast that sets off the avalanche.

last updated 8-Feb-2008

I ski on the piste, why should I be bothered about avalanches?

Many of the accidents resulting in deaths have occurred right next to the piste, due to ignorance. They could therefore have been avoided. If you are a good skier or snowboarder who mostly skis on the piste and you play around next to the piste, then you are a prime candidate for an accident. The same goes for climbers: statistics show that the typical victim of an avalanche is a male in his mid-late 20's, has a good level of knowledge about skiing, boarding or climbing, but very little knowledge about avalanches.

last updated 8-Feb-2008

What kind of avalanche is most dangerous?

Dry slab avalanches account for almost all avalanche fatalities. In the northern hemisphere, these accidents happen in winter conditions (December to mid-March) and most often on north-facing slopes.

last updated 8-Feb-2008

What kind of weather produces avalanches?

Wind is the most common cause of acute instability. Wind can deposit snow 10 times faster than snow falling during storms. Wind erodes snow from the upwind side of obstacles and deposits snow on the downwind (lee) sides. We call this "wind loading".

The added weight from this "wind loading" also causes avalanches. If the weight of new snow is added faster than a buried weak layer can adjust to its load, then it fractures and forms an avalanche. Rapid warming can also cause dry avalanches but this is a much rarer occurrence.

Rain or melting of the snow surface can also cause avalanches. For instance, rain on new snow almost instantly causes avalanches. Strong sun or warm temperatures can also cause melting of the snow and creates wet avalanches. Large wet avalanches occur because of a decrease in strength of a buried weak layer as a result of water dissolving the bonds between the snow grains.

But wind, snow or rapid warming do not always produce avalanches. It depends on the condition of the pre-existing snow and the conditions during the storm. With very stable pre-existing snow, even heavy, new snow with wind can bond well and be perfectly safe in the right conditions.

last updated 8-Feb-2008