avalanches

• Loose snow avalanches (point release):

  • recent snow has little cohesion
  • gravity causes high shear stress so snow slides off steep slopes
  • not very destructive
• Windslab (slide):

  • snow is blown by wind then deposited
  • new snow binds to itself, but not to old snow below it
  • limited shear strength as a small addition of stress makes slab lose cohesion and slide off the snow below
• Airborne powder avalanche:

  • slab and loose snow avalanches can become airborne if moving fast over a cliff
  • blast wave precedes snow as a cloud
  • blast wave can be very destructive
• Wet loose snow avalanche:

  • temperatures rise so snow melts forming water
  • water is absorbed by snow which increases weight, which increases shear stress
  • water reduces cohesion
  • avalanche occurs spontaneously with no trigger in the afternoon
• Slab avalanche:

  • water from snowmelt or precipitation penetrates snow and lubricates the gaps between layers
  • reduces shear strength
  • causes a slab of snow to slide