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Wind slabs

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What?

Characteristics

Wind slabs are formed when loose snow in near-surface layers (new snow or old snow) is transported by wind.

Expected avalanche types

  • Dry‐snow slab avalanches
  • Natural and human triggered avalanches possible

Where?

Spatial distribution

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

Position of the weak layer in the snowpack

Usually between wind slabs and old snow, i.e. close to the interface to the old snow surface or within the slab layers due to variations in wind speed during storm cycle, but occasionally also slightly below in the old snowpack. In the latter case, the problem “persistent weak layers” additionally prevails.

Why?

Release characteristics

The wind slab is an additional load on a weak layer and builds a slab that is particularly prone to support crack propagation.

When?

Duration

The wind slab problem can evolve very quickly. The problem lasts typically during the snowdrift event and and tends to stabilize within a few days following the storm cycle. Cold air temperatures can extend the persistence.

How to manage?

Identification of the problem in the field

If not buried by new snow, the wind slab problem can be recognized with training and good visibility. Consider wind signs and locate deposits. Typical clues: snowdrift deposits, recent avalanche activity and sometimes shooting cracks or whumpfs. However, it is often hard to determine the age of snowdrift deposits and wind signs do not necessarily imply an avalanche problem (e.g., in absence of a weak layer).

Travel advice

Avoid snowdrift deposits in steep terrain.

Typical accident

Juferhorn, Avers (GR), 3 January 2012