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How do avalanches start?
Answered by Discovery Channel
  • Discovery Channel

    Discovery Channel

  1. Every avalanche has three basic parts: a starting zone, its track and its runout. The starting zone is where the slab of snow first breaks away from the slope. The starting zone usually falls above a tree line and near a ridge. The track of the avalanche is the path the slab takes down the mountain. You can see evidence of an avalanche's track because there will often be nothing else there, such as a gap between spans of trees. Lastly, the runout is where the snow slabs and the debris they've picked up along the track finally come to a stop.

    Every avalanche needs a trigger to get started. Either natural or man-made actions can cause avalanches. Some natural avalanche triggers are falling trees, changes in weather or collapsing cornices (an icy overhang of snow near a ridge). Human activity can trigger an avalanche; most winter sport adventurers like to hit the backcountry, exactly the kind of pristine, steep slopes that have perfect avalanche conditions. Most people who are killed by avalanches are men in their 20s who are experienced backcountry sportsmen [source: Colorado Avalanche Information Center]. High marking - - driving a snowmobile as high up a steep slope as possible and then arcing back down - - is another example of human action that can trigger an avalanche.

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