Wet snow - loose snow avalanches

Be careful in avalanche release and runout areas. Avoid terrain traps. For danger level 3: Avoid avalanche release and run out areas.

Wet snow avalanches tend to release spontaneously.

Stability decreases when the snow surface gets wet and soft.

Timing is important

Characteristics

  • The avalanche problem is related to wetting and weakening of the snowpack due to the presence of liquid water. Water infiltrates the snowpack due to melt or rain. 
  • The problem can occur due to rain, sun, warm temperatures or lack of refreezing of the snowpack at night.
  • Avalanches is formed lika a drop, can vary in size from small to large. Runout length can be very long with high water content.

 

Spatial distribution

  • When sun is the main cause, distribution of the problem is mostly depending on aspect and elevation.
  • All aspects are affected in the event of rain on snow.
  • Releases most often in terrain steeper than 40 degrees, often close to rocks/cliffs.

 

Trigger mechanisms

  • Warming leads to melting and loss of cohesion between snow particles.

 


 

Duration

  • Hours to days, depending on temperature, precipitation and radiation.
  • Rapid loss of stability possible.
  • If sun is the cause (typical spring conditions) - the danger increases during the day, most avalanches occur in afternoon when the temperature is higher.
  • If rain is the cause, the danger increases when the rain starts.

 

Identification of the problem

  • Usually easy to recognize, the snow surface is wet.
  • Wet and soft snow surface, onset of rain, snowballing, pin wheeling and recent loose wet avalanches are signs of instablity.
  • Deep foot-penetration is another sign of increased wetting.

 

Loose wet avalanche in Jostedalen. Photo: Jostein Aasen.