Nevado Del Ruiz Eruption 1985

Primary and Secondary Effects

  • Lahars killed 70% of Armero’s population 45km away.
  • Lahars were as much as 40m thick and travelled at 50km per hour.
  • Most killed by suffocation as lahars up to 8m buried them.
  • Lahars killed 1,800 people in Chinchina.
  • 3400 ha of agricultural land was lost.
  • Infrastructure destroyed.
  • Hot pyroclastic flows and surges caused rapid melting of snow and ice creating hot lahars.
  • Region was isolated.
  • Fifty schools and two hospitals damaged and destroyed.
  • $7.7billion cost of the damage.
  • Clean water in short supply.
  • Mobility in the valley was limited.



  • Primary waves (P) – are body waves that pass through the earth along paths. P waves are compressional longitudinal waves similar to sound waves in which particles vibrate parallel to the direction of movement.
  • P waves pass through solids, liquids and gases, and the velocity of P waves depend on density and resistance to compression of the medium it passes through.
  • While, P waves will pass through the centre of the Earth, they will be refracted by the changing density of the mantle, outer core and inner core.
  • This causes the wave to bend and helps explain the formation of the shadow zone. Shadow zones happen between P waves that have been refracted and a wave that hasn’t. S waves don’t have shadow zones as these are absorbed by the outer core.

Primary Effects of an Earthquake

  • Buildings and bridges collapse.
  • Infrastructure is destroyed.
  • People are injured or killed.
  • Damage to cables, water pipes etc.


Secondary Effects

  • Businesses are destroyed leading to unemployment.
  • Exposed gas pipes could cause potential fire.
  • Lack of clean water.
  • Spread of disease.
  • People left homeless.
  • Earthquakes can trigger landslides and tsunamis.