Friday, 10 January 2014
There have been several deadly avalanches recently in the Western Alps. Notably in the Valais region of Switzerland where 4 people were killed last weekend. Many are saying this is the most dangerous snowpack in decades, and others are calling for a ban on off-piste activities.
The weakness in this winter's snowpack has been caused by the unusual weather at the start of the season. Late November there was heavy snowfall, followed by over three weeks of high pressure. Cold temperatures, combined with a shallow snowpack, resulted in a "steep temperature gradient". This is the rate at which the temperature changes as you go from the air, through the snowpack, to eventually reach the ground. In layman's terms, the more rapid the change, the more likely weak crystals will develop. These "facets" are delicate, and don't bond together. Hence they provide an ideal sliding surface for a stronger layer above.
I read an article by Peter Hardy, ski correspondent for the Daily Telegraph, stating that he would not be going into the backcountry this winter as the risk was unjustifiable. However, I think many people are simply missing the point. The backcountry is never 100% safe. There is always a degree of risk, and that risk must be managed.
Certain slopes are more prone than others to avalanche. 30-45 degrees is the optimum angle for avalanches to occur. Hence in high risk conditions you should stay on low angle slopes.
Understanding the exact location of weaknesses within the snowpack is essential. Avalanche Bulletins for the Mont Blanc region clearly state that shady slopes between 2000m and 3000m have a high risk of weak facetted layers which could easily be triggered by skiers. So, don't ski steep slopes, on Northerly aspects, between 2000m and 3000m. With this simple strategy you have reduced the risk enormously.
Below 2000m, and on Southerly aspects above 2000m, recent warm temperatures and the warming effect of the sun have melted most of these facets to form a strong layer within the snowpack.
Above 3000m the risk is currently lower still as the permanent snowcover at that altitude meant that facets did not form there. Hence on Wednesday I guided a descent of the Vallee Blanche and experienced exceptionally good snow. A perfect 500m slope of untracked powder, above 3000m was all ours - and it felt fantastic ! If you don't believe me, just have a look at the picture.
In most cases, recent fatal avalanches occurred in the exact places described by the avalanche bulletin as being most dangerous. Unfortunately many people read the bulletin, but do not actually apply it to their Trip Planning for the day.
The experience of the off-piste and backcountry is something many people dream of for most of the year. It is dangerous, but with planning and a careful approach throughout the day, these risks can be managed, allowing people to enjoy the whole mountain and not just the groomed pistes. Rather than recommending people not to go off-piste I firmly believe that people should get educated about the dangers of avalanche so that they can learn how to manage the hazards for themselves.
Have a safe winter....