Be careful and keep distance to each other in steep (above 30 degrees) terrain with fresh wind deposited snow, especially convex terrain.

If danger Level 3-considerable, avoid steep (more than 30 degrees) areas with fresh wind deposited snow, especially convex terrain.

An avalanche is easier to trigger where wind slabs are thin or soft.

Look for areas where the wind recently has deposited snow, typically behind ridges, ribs and in gullies. Remember that local wind effects will cause variation in where the wind slabs occur.

Wind-drifted snow

Characteristics

  • The avalanche problem is related to wind-drift of loose snow already lying on the ground (Wind during a snowfall is characterized under the Storm slab Avalanches problem
  • Avalanches vary in size and hardness depending on wind speed and amount of loose snow available for transport.

 

Spatial distribution

  • Highly variable but typically on leeward sides, in gullies, bowls, near distinct changes in slope angle, behind ridgelines or other wind-sheltered locations.
  • More common above treeline.

 

Release characteristics

  • Wind-drifted snow builds a soft or hard slab which is particularly prone to support crack propagation.
  • Loading of wind-drifted snow leads to potential fracture in weak layers.

 

Possible weak layers

  1. Poor bonding between layers in wind deposited snow
  2. Buried weak layer of new snow

 

Duration

  • Wind slabs can evolve very quickly.
  • The problem lasts typically during the snowdrift event and up to a few days later, depending on temperature and radiation.

 


 

Identification of the problem

  • If not hidden by new snow the wind-drifted snow problem can be recognized with training and good visibility.
  • Consider wind signs and locate deposits.
  • Can often be recogniced by change in the snow consistence and chages in snow hardness.
  • However, it is often hard to determine the age of wind signs and wind signs do not necessarily imply an avalanche problem (e.g., in absence of a weak layer).
  • Typical clues:
    • Wind signs on the surface
    • snowdrift deposits, soft or hard
    • recent avalanche activity
    • shooting cracks 
    • whumps (rarly)

 

Drifting snow in Lofoten. Photo: Ragnar Ekker