SNOW AVALANCHE

About: 

• Meaning: The snow avalanche, a common occurrence in snow covered mountainous regions, is a slide of snow mass down a mountainside. This is a rapid downslope movement of a large detached mass of snow, ice, and associated debris such as rocks and vegetation. 
  
  
• Types: There are two basic types of avalanches – 
  • Loose snow avalanches form in snow masses with little internal cohesion among the individual snow crystals. 
    
    
  • Slab avalanches originate in snow with sufficient internal cohesion to enable a snow layer, or layers, to react mechanically as a single entity. 
    
    
  
  
  
• Causes: 
  • Avalanches form as soon as the force of gravity on the snow cover exceeds its mechanical strength. To be caused, an avalanches needs a steep slope, snow cover, a weak layer in the snow cover, and a trigger to initiate movement. 
    
    
  • Snow avalanches may occur on any slope where enough snow is deposited in the right circumstances. Snow does not accumulate significantly on steep slopes; also, snow does not flow easily on flat slopes. 
    
    
  • Most avalanches of dangerous size therefore originate on slopes with inclinations of between 30 degrees and 45 degrees. 
    
    
  
  
  
• Impact of Snow Avalanches: 
  • The forces generated by moderate or large avalanches can damage or destroy most manmade structures. The debris from even small avalanches is enough to block a highway or rail-road. 
    
    
  • A large avalanche can run for many kilometres, and result in massive destruction of forests and anything else that comes in its way.