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HUMANITIES YEAR 9: AVALANCHES

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HUMANITIES YEAR 9: AVALANCHES

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HUMANITIES YEAR 9: AVALANCHES

  1. 1. AVALANCHES YEAR 9 HUMANITIES
  2. 2. DEFINITION Avalanches are masses of snow, ice, and rocks that fall rapidly down a mountainside. While avalanches are sudden, the warning signs are almost always numerous before they let loose.
  3. 3. THE TRIGGER In 90% of avalanche incidents, the snow slides are triggered by the victim. Avalanches kill more than 150 people worldwide each year. Most are snowmobilers, skiers, and snowboarders.
  4. 4. THE SPEED Disastrous avalanches occur when massive slabs of snow break loose from a mountainside and shatter like broken glass as they race downhill. These moving masses can reach speeds of 130 km per hour within about five seconds. Victims caught in these events seldom escape.
  5. 5. THE WINTER ARCHIVE Avalanches are most common during and in the 24 hours right after a storm that dumps 30 cm or more of fresh snow. The pileup overloads the underlying snowpack, which causes a weak layer beneath the slab to fracture. The layers are like an archive of winter weather: big dumps, drought, rain, a hard freeze, and more snow. How the layers bond often determines how easily one will weaken and cause a slide.
  6. 6. FACTORS INFLUENCING AVALANCHES Storminess, temperature, wind, slope steepness and orientation (the direction it faces), terrain, vegetation, and general snowpack conditions are all factors that influence whether and how a slope avalanches. Different combinations of these factors create low, moderate, considerable, and high avalanche hazards.
  7. 7. WHAT TO DO IN AN AVALANCHE? If caught in an avalanche, try to get off the slab. In most instances, this is not easy. Skiers and snowboarders can head straight downhill to gather speed, then veer left or right out of the slide path. Snowmobilers can punch the throttle to power out of harm's way. No escape? Reach for a tree. No tree? Swim hard. The human body is three times denser than avalanche debris and will sink quickly. As the slide slows, clear air space to breathe. Then punch a hand skyward.
  8. 8. CHANCES OF SURVIVAL Once the avalanche stops, it settles like concrete. Bodily movement is nearly impossible. Wait—and hope—for a rescue. Statistics show that 93% of avalanche victims survive if dug out within 15 minutes. Then the survival rates drop fast. After 45 minutes, only 20 to 30% of victims are alive. After two hours, very few people survive.

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