Unit 4 Tectionic activity- physical impacts


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Caldera Volcano

  • formed in two ways;
    • collapse of surface rock into empty magma chamber 
    • explosive volcanic eruption 
  • Explosive caldera formation
    • very large magma chambers filled with silica-rich melt and abundant gas move upwards from depth.
    • very high viscosity that enables them to hold gas bubbles under very high pressures.
    • As it rises to the surface the reduction of pressure causes the gases to expand.
    • break-through occurs the result can be an enormous explosion which blasts away large volumes of rock to form the caldera.


  • Crater Lake Oregon
  • Yellowstone supervolcano
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Hawaiian Eruption

  • fluid basaltic lava
  • released through vents (fissures)
  • low magnitude due to constant release of pressure 
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Strombolian eruption

  • Distinct bursts of fluid lava (basaltic-andesite)
  • Explosions usually occur every few minutes at regular or irregular intervals
  • Explosions are due to trapped gas bubbles 
  • Producces tephra
  • Least violent of explosive eruiptions
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Fissure Volcano

  • volcanic eruption from fracture in earths surface
  • underlain by reservoirs of basaltic magma
  • Mid-oceanic ridges- divergent plate boundaries


  • Iceland, an extention of the Mid-Atlantic ridge
  • Hawaiian shield volcanoes
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Composite Volcano

  • Steep-sided and cone-shaped
  • Made up of layers of ash and lava 
  • Andesitic// Ryolitic lava


  • Mount Etna Italy
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Sheild Volcano

  • Typically hot spot locations where the crust is particually thin or weak
  • Balsitic lava
  • Only explosive if water gets into vents 
  • Gasses escape very easily 
  • Gently sloped & made from layers of lava


  • Mauna Loa Hawaiian islands 
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Dome Volcano

  • Formation; within stratocolcanos 
    • large eruptions empty out the magma chamber in the summit of the composite volcano.
    • It collapses forming a depression.
    • Inside the depression magma oozes out to begin forming a small lava dome.
  • Formation; steep sided volcanosAndesitic/ Rhyolitic lava
    • Lava domes form on the steep sides of volcanoes
    • they can become dislodged during an eruption
    • most dangerous type of lava domes due to exposure of molten rock that become pyroclastic flows as the gases are released


  • Mt St Helens 
  • Mt Pelee Caribbean 
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Cinder Cone Volcano

  • Smallest and most common volcano
  • Occurs in basaltic lava fields or parasitic cones on stratovolcanoes or shield volcanoes.
  • Balsitic lava released 
  • Tephra released if gas is trapped
  • Cinder cones generated by strombolian eruptions


  • Sunset crater Arizona US
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Vulcanian Eruption

  • Short, violent and relatively small explosion of viscous magma
  • Andesitic lava
  • Produce tephra, ash clouds, and pyroclastic flows
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Plinian Eruption

  • Largest and most violent of all eruption types 
  • Caused by the fragmentation of gassy very viscousmagma
  • Rhyolitiic magma
  • Releases enormous amounts of energy
  • Produce falls of ash, scoria and lava bombs and pyroclastic


  • Mt St Helens
  • Mt Vesuvius
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Intrusive Igneous Activity

Intrusive igneous activity- materials injected into the crust are intrusive landforms, which are exposed through erosion or overlaying rock.

Sills: Whin N- England

  • parallel bedding planes 
  • cracks run horozantally and provide lines of weakness where magma flows 
  • As it cools, the magma contracts providing cracks in the rock

Dykes: Channel Islands 

  • Cut accross the bedding planes of rock 
  • Magma forms cracks and weaknesses.
  • It cools and solidifies before reaching the surface forming liniar ridgs where its exposed.

Batholith: Dartmoor

  • Large masses of intrsive rock 
  • Forms doming on surface
  • Heat transfered from the magma created metamorphic rock.
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