Defensive Mountaineering

Avalanche

 

slab

Photo copyright: Bruce Jamieson Slab avalanche. The fracture line is at the steepest part of a lee slope and close to the crest of the ridge.

The sky is blue. It’s the first day of good weather after days of snowfall. It’s bitterly cold. The snow sparkles in the sun. How soft and loose it was on the climb. New snow! Powder!

The pull up to the summit was hard work and now the team are all raring to go. Others already shout and whoop as they ski the powder below. “Come on! What are you waiting for?” So go for it! Ten meters in you glide in the lee of the ridge.

Beautiful! Magic! You shout with joy! Turn, turn, turn. Ecstasy…

‘WHUMM!’ Your heart misses a beat. A crack in the snow rips open. Fear grabs your gut. You slide out of control. All is confusion. Snow covers your face. You fight in panic. Too late! Avalanche!

Yet… all the alarm signs had been there to see…


Many, many accidents occur on days when the weather is pleasant: generally clear skies, little or no snowfall and light or calm winds. A high proportion occur just after new snowfall.

Human frailties rank high in the causes of avalanches. Ambition; itineraries; expectations; peer pressure. The perfect run… That virgin steeper snow beside those new tracks…Grab the chance now before the snow is skied out…

The Canadian Avalanche Association have shown that most avalanches are dry slab avalanches, with an average thickness of less than 100cm, 45% after just 10cm of new snow. Most are triggered by the victims or members of the victim’s party. The weak layer often consists of surface hoar, faceted snow crystals , graupel, or depth hoar.

The majority of accident avalanches start above or near the tree-line on lee (67%) or cross slopes where the wind has scoured across the surface (31%). Windward slopes account for just 2% of avalanches. Most avalanches (69%) start on 30°-40° slopes, often on convex slopes, often with exposed rocks that cause stress concentrations, and often near the crest of a ridge. Only 6% happen on slopes of less than 25°.

The typical avalanche victim is male, in his twenties.

Ski mountaineering is a dangerous sport and precautions must be taken. Training in basic skills. Refreshing skills and knowledge every year. Specialised equipment, clothing, planning and assessment of snow conditions, to minimise or avoid risk.

Knowledge of snow and the factors affecting avalanches is indispensable.The chances of surviving burial in an avalanche diminish rapidly after the first five minutes of burial. The ability to locate and dig out an avalanche victim is essential and must be refreshed regularly by practice.

Essential equipment to enable immediate search and rescue to be attempted in the event of an avalanche burying a companion includes:

  • an avalanche rescue transceiver,
  • a lightweight metal snow shovel, and
  • an avalanche probe

Transceivers are by far the most effective way of locating victims (44%), but do not prevent avalanches. A false sense of security imparted through wearing a transceiver might even contribute to an avalanche. They are an aid to rescue only.

Whilst it is important to learn and practice disciplined avalanche search and rescue, what is far more important is to avoid avalanches completely.

 

Defensive Mountaineering