Types of avalanches

Winter dry snow avalanches

o Snow sluff or point release avalanche

  • Usually,
    • They are confined to new snow
    • They are a sign of stabilization
    • They can (but rarely do) bury people
  • Release from a "point"
  • Fan out as they move down the hill

o Slab avalanche

  • These are the dangerous variety of avalanches
  • They initiate when a cohesive block of bonded snow fails
  • Slabs range from 10 cm to as much as several meters deep
    • Soft slabs pulverize during the avalanche
    • In hard slab avalanches, large blocks of snow remain intact
  • Slab avalanches are rated on a scale of 1-5.
    • Class 1 are small and generally not dangerous to skiers
    • Classes 2 and 3 are most common in fatal avalanches for skiers
    • Classes 4 and 5 generally too large to survive
  • Typically...
    • The snow density is 28% in a slab - ratio of snow mass to water mass
    • 80% of all slab avalanches occur on 30-45 degree slopes
    • 38 degree incline most common
  • Friction during avalanche causes debris to be very firm

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