Volcanic hazards

• Spatial distribution of volcanoes


  • Occur mostly on tectonic plate margins- especially subduction zones or hot spots
  • E.g. ring of fire in Pacific Ocean
  • Found along mid-ocean ridge system- oceanic plate diverge, magma spreads on ocean floor
• Volcanic explosively index (VEI)


  Measure of vulcanicity, scale X10 each time
• Volcano classification by frequency


  • Active
  • Dormant
  • Extinct
• Higher frequency volcanoes


  Lower magnitude (effusive) due to less build up
• Lower frequency volcanoes


  High magnitude
• Explosive (Plinian) eruption


  • Gas driven
  • Propels magma and tephra
• Effusive (Hawaiian) eruption


  • Outpouring of lava
  • No significant eruption
• Volcanic hazards


  • Lava flows
  • Lahars (mudflow)
  • Glacial floods
  • Tephra
  • Toxic gases
  • Acid rain
  • Pyroclastic flows
• Lava flow speed


  Quick or slow depending on viscosity, silica makes lava viscous
• Lahars (mudflow)


  Usually caused by ice melting at high latitudes
• Glacial floods


  High temp can melt glaciers, causes floods
• Toxic gases


  CO2 can be toxic as it can replace O2- heavier
• Acid rain


  Caused by gases such as sulphur dioxide released
• Pyroclastic flows


  Clouds of hot ash and gas that collapse down volcano at high speed, can reach 430mph