5.6

• Volcanic debris avalanches


  Landslides that occur in volcanic slopes
• Volcanic debris avalanches


  • Abnormally large volumes of volcanic material traveling at great speeds
  • Bury areas far and wide
  • Considered the worst-case scenario for volcanic hazards

  
• Volcanic landslides range in size from less than 1 km3 to more than 100 km3

  
• A nonvolcanic landslide may reach a horizontal distance of 166 m for every 100 m it descends vertically, but volcanic debris avalanches can reach as far as 1000m horizontally for the same amount of vertical drop

  
• Debris avalanche danger zones and mitigation


  1. Anticipate the coming of a debris avalanche as much as possible

  2. Identify areas prone to debris avalanches through hazard maps
• Debris avalanche events are difficult to anticipate due to too many unknowns associated with magmatic systems and seismicity
• The 1980 debris avalanche at Mt. St. Helens was preceded repeatedly by earthquakes within two months before the failure of its northern sector

  
• What to do before, during, and after an eruption

  1. Before: Monitor volcanic activity, prepare evacuation plan, fireproof house, participate in community efforts

  2. During: Evacuate to designated shelters, use gas mask, stay alert for advisories

  3. After: Proceed with caution, participate in community efforts to restore necessities, maintain peace and order