Avalanche Information

Avalanche Information

Weather conditions dictate the possibility of an avalanche. They are most likely to occur either during or immediately after a storm where there has been a significant increase in snowfall. In fact, the most critical period of time is the 24 hours after a heavy snowstorm. Consequently, it becomes important to be aware of current weather conditions as well as the conditions from the previous couple of days.

Temperature as well as wind speed are determining factors. If a SW wind of 25 mph is indicated with freezing temperatures and snow known to be lying, then it may be assumed that some avalanche hazard will be building on NE - facing slopes. In the event of an avalanche, you are very unlikely to be able to move out of its path or out run it. An average avalanche travels at speeds of around 80 mph and making a run for it is usually impossible.

It is unlikely that a recreational skier spending a week or two on the slopes will be caught up in an avalanche. The following information may just be read as a point of interest but some safety points absorbed should the unlikely become reality!

Types of avalanche

The most common avalanche during the spring time or in thaw conditions is the Wet Avalanche. It is caused by water flowing through or between the snow and the ground. This causes weakening of the structure between ground and snow. It is the resulting movement of snow and water, although at a slow speed, which causes the problem as the weight steadily increases. Detection is possible through cracks in the snow and the formation of large rolling snowballs.

The most common type of avalanche associated with the build up of fresh snow is the Soft Slab Avalanche. After a heavy snowfall it could occur on any slope as the snow is moved by the wind of 10-30 mph. The slab is released as a single piece and breaks up as it moves. If there is enough fresh snow and the slope is steep then it could evolve into a Powder Avalanche.

The Dry Powder Avalanche is most common in cold and dry conditions especially after a fresh snow fall. It becomes even more common after a fall of 2cm or more. The snow ride up on a cushion of air and so become airborne travelling in excess of 100mph a blast wave will be heading up the avalanche.

The Hard Slab Avalanche formed if there is a combination of strong winds of more than 30 mph and a very cold temperature. This one is the most unassuming but deadly of avalanches. It appears solid to skiers travelling over it. The slab can be covered with fresh snow and eventually release itself in one piece but then breaks up into huge chunks of snow and ice. Usually detected by sudden local subsidence and dull booming noises.

LOW RISK - Green in both American and European scales

  • Snowpack is generally stable
  • Only isolated areas of instability
  • Backcountry travel is fairly safe
  • Natural or human-triggered avalanches unlikely

MODERATE RISK - Yellow in both American and European scales

  • Some areas of instability
  • Natural avalanches unlikely; human-triggered avalanches possible
  • Backcountry travel possible with caution

CONSIDERABLE RISK - Orange in American scale, Ochre in European scale

  • Unstable areas probable
  • Natural avalanches possible; human-triggered avalanches probable
  • Backcountry travel possible with extreme caution

HIGH RISK - Red in American scale, Orange in European scale

  • Unstable areas highly likely on various slopes and aspects
  • Natural and human-triggered avalanches highly likely
  • Backcountry travelers should avoid steep slopes and wind-loaded slopes

EXTREME RISK - Black in American scale, Red in European scale

  • Extremely unstable layers in snowpack
  • Natural and human-triggered avalanches are certain
  • Large destructive avalanches probable
  • Backcountry travelers should avoid any steeply angled terrain or known avalanche areas

If caught in an Avalanche

In most avalanche situations, any defensive action is very difficult. Movement relative to the debris is often impossible. However, some of the following may be useful:

  • Try to delay departure by plunging an ice axe into the undersurface. This may help to keep you near the top of the slide.
  • Shout. Others may see you.
  • Try to run to the side, or jump up-slope above the fracture
  • If hard slab, try to remain on top of a block.
  • Get rid of gear; sacks, skis etc.
  • Try to roll like a log, off the debris.
  • Swimming motions sometimes help.
  • As the avalanche slows down, you may be able to get some purchase on the debris. Make an effort to get to the surface, or at least get a hand through.

If buried:

  • Keep one hand in front of you face and try to clear/maintain an air space.
  • Try to maintain space for chest expansion by taking and holding a deep breath.
  • Try to avoid panic and conserve energy. Your companions are probably searching for you.

Avalanche rescue

If you witness an avalanche burial:

  • Observe the victim's progress and if possible mark the point of entry and point at which last seen.
  • Check for further avalanche danger.
  • Make a QUICK SEARCH of the debris surface.
    • LOOK for any signs of victims.
    • LISTEN for any sounds.
    • PROBE the most likely burial spots.
  • Make a SYSTEMATIC SEARCH, probing the debris with axes or poles.
  • Send for Help.
  • KEEP SEARCHING until help arrives.

REMEMBER YOU ARE THE BURIED VICTIM'S ONLY REAL CHANCE OF LIVE RESCUE.

Although survival chances decline rapidly with duration of burial, they do not reach zero for a long time.