Types of Volcano

• Volcanicity


  All volcanic activities related to magma being forced into the crust, usually at plate margins
• Magma at high temperatures and pressures

  1. Exploits weaknesses in the crust

  2. May erupt to the surface as lava
• Types of volcanoes


  • Active
  • Dormant
  • Extinct
• Active volcano


  An eruption is currently ongoing
• Dormant volcano


  Not erupted in the last 10,000 years
• Extinct volcano


  Not going to erupt again
• Methods of categorising volcanoes

  • Shape of volcano
  • Nature of the eruption
• Volcano shapes based on lava type

  • Basaltic
  • Andesitic
  • Rhyolitic
• Basaltic lava


  45% silica content
• Andesitic lava


  52% silica content
• Rhyolitic lava


  66-75% silica content
• Fissure volcano


  • Occur at divergent plate boundaries
  • Lava can be ejected through fissures rather than a central vent
  • Lava tends to form large plateaus, filling in hollows rather than building up
  • Basaltic lava
• Fissure volcano


  • Laki Fissure system, Iceland
• Acid/dome volcano


  • Acid lava solidifies on exposure to air
  • Produces a steep sided, convex cone
  • Lava solidifies as it comes up the vent and produces a spine
• Acid/dome volcano


  • Mt Pelee
• Basic/shield volcano


  • Often occur at divergent plate margins or hot spots
  • Lava flows out of a central vent and spreads over wide areas before solidifying
  • Cone with long, gentle sides made up of many layers of lava
  • Runny basaltic lava
• Basic/shield volcano


  • Mauna Loa
• Composite volcano


  • Classically shaped volcanoes from alternating ash and lava eruptions
  • Found at convergent boundaries
  • May have violent eruptions followed by more gentle ones
• Composite volcano


  • Mt Etna
• Ash/Cinder cone volcano


  • Ash or cinder builds into a symmetrical cone
  • Often found at the bottom of shield volcanoes and calderas
• Ash/Cinder cone volcano


  • Paracutin
• Caldera


  • Build up of gases causes huge explosions that clear the magma chamber and allow the sides to collapse inwards
• Caldera


  • Krakatoa, Yellowstone, Flangerian Fields
• Icelandic eruption


  • Persistent eruption along a fissure
  • Large quantities of basaltic lava build up vast horizontal plains
• Icelandic eruption


  • Deccan Plateau, Columbian Plateau
• Hawaiian eruption


  • More noticeable central activity than Icelandic
  • Runny basaltic lava travels down the sides in flows
  • Low silica content
  • Gases escape easily
  • Can form fire fountains
  • Occasional pyroclastic activity
• Strombolian eruption


  • Frequent gas explosions blast fragments of runny lava into the air
  • Smallest type of explosive eruption
  • Eject short bursts of lava 15-90m into the air
  • Eruptions marked by white steam cloud
• Vulcanian eruption


  • Violent gas explosions blast out plugs of sticky or cooled lava
  • Fragments build up into cones of ash and pumice
  • Occurs when viscous lava solidifies rapidly after an explosion
  • Often clears a blocked vent and spews ash
• Vesuvian eruption


  • Powerful blasts of gas push ash clouds high into the sky
  • More violent than Vulcanian
  • Lava flows and ash falls cover surrounding areas
• Plinian eruption


  • Most explosive and violent volcanic eruptions
  • Magma has high silica content
  • Gas rushes up through sticky lava and blasts ash and fragments into the sky
  • Creates immense clouds of gas and volcanic debris
  • Part of the volcano may be blasted away
• Plinian eruptions are named after Pliny the Younger who wrote about the 79AD eruption of Mt Vesuvius