VOLCANOS

• what is the viscosity of the magma at a sheild volcano

  low viscosity (BASALT)
• name 2 examples of SHEILD volcanos

  Nyriagongo and Eyjafjallajokull
• viscosity of lava in a composite volcano

  high viscosity
• type of lava in a composite volcano

  rhyolite
• VEI of shield volcano

  lower VEI 4
• VEI of composite volcano

  high VEI 6-8
• nuees ardentes


  fast moving cloud of ash and larger material that flows down the volcano
• pyroclastic flow


  high density mass of gases and ash and larger material that flows down the volcano
• lahar


  mudflows composed of pyroclastic material and water
• volcanic bomb 


  rocks more than 5mm in diameter thrown in the air by the eruption
• acid rain


  rain made acidic by pollutants in the air
• tephra 


  rocks ejected from a volcano during an eruption
• ocean ridge.. 


   plates move apart causing magma to rise up onto the surface forming a volcano (CONSTRUCTIVE PLATE BOUNDARY)
• subduction zone forming volcano...

   Denser oceanic plate subducts, melts and becomes less dense and so convects back to the surface to form a volcano.
• rift valleys forming volcanos...

   brittle crust fractures as plate move apart, crust thins and areas of crust drop down between parallel faults. magma rises and forces its way to the surface to form volcanoes.

  e.g. Nyriagongo
• How many different eruption types are there?

  7
• What characterizes a Vulcanian eruption?

  Moderate explosions with gas and ash
• What is a key feature of a Pelean eruption?

  Generates pyroclastic flows with hot fragments
• What type of volcano is formed by Hawaiian eruptions?

  Shield volcanoes
• How often do Vesuvian eruptions occur?

  Very infrequently
• What is the nature of Strombolian eruptions?

  Moderate bursts of gas and lava
• What type of lava flow is characteristic of Icelandic eruptions?

  Molten basaltic lava from fissures
• What distinguishes a Plinian eruption?

  Intensely violent gas-rich magma blasts
• How do Plinian eruptions differ from Vulcanian eruptions?

  Plinian eruptions are intensely violent
• What type of eruption would likely produce a large ash cloud over a wide area?

  Vesuvian eruption
• If you observe a volcano with gentle slopes, which eruption type is likely responsible?

  Hawaiian eruption
• What is the primary difference between Strombolian and Pelean eruptions?

  Strombolian eruptions have moderate bursts
• What type of eruption is characterized by low viscosity lava flowing at great velocities?

  Pelean eruption
• What type of eruption produces a gigantic rocket blast directed vertically upwards?

  Plinian eruption
• What is a common feature of all eruption types mentioned?

  They all involve volcanic activity
• viscosity is dependent on...

   silicon content and temperature. High silicon content = high viscosity. High temp = low viscosity. 

  High viscosity - hard for gases to escape so magma forced upwards, violent explosive reaction when magma and gas is released.
• what type of lava is at the oceanic crust

  balsatic lava- low viscosity and effusive eruptions
• what type of lava is at continental crusts

  andesitic lava- high viscosity and effusive eruptions