Tectonics

• basaltic lava


  Hottest (1000-1200C), low silica/gas content, low viscosity (runny), gentle/effusive
• andesitic lava


  Type of magma with a medium amount of silica content/ viscosity.
• rhyolitic lava

  Coolest (650-800C), high silica/gas content, high viscosity, very violent
• what helps to create composite volcanoes

  high viscosity lava with a high silica content (rhyolitic) as the lava cannot travel far.

  
• what helps create shield volcanos

  low viscosity lava with a low silica content (basaltic) which allows the runny lava to travel far from the vent.
• why are composite volcanoes more violent

  rhyolitic lava which sets quickly effectively seals off the magma and cases creating high pressure.
• What is a cinder cone volcano?

  A steep, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs piled up around a shield or composite volcano's opening

  
• primary volcanic hazards

  - Pyroclastic flow- fast-moving current of hot gas and volcanic matter that flows along the ground away from a volcano at average speeds of 100 km/h

  - Lava

  - Tephra, rock fragments and particles ejected by an eruption.

  - Volcanic gases, carbon dioxide, sulfur dioxide, hydrogen sulfide. can settle and suffocate people or livestock

  - volcanic ash
• secondary volcanic hazards

  - lahars (mud flows with volcanic ash and rock) caused by melting snow and volcanic material or heavy rain after a volcanic event

  -jokulhlaups- melting of glaciers due to volcanic activity leads to the creation of glacial lakes that eventually become too large and flood. (glacial outbursts)
• two types of crust

  continental crust and oceanic crust
• What is the lithosphere?

  the crust and solid upper part of the mantle.

  the rigid part of the earth
• what is the Asthenosphere

  The asthenosphere is the part of the mantle just beneath the crust. It is viscous which means it can flow.
• what is the moho discontinuity

  boundary between crust and mantle
• what forms the inner and outer core

  The outer core is a layer of liquid iron and nickel. The heavier metals have sunk to the centre of Earth, beneath the lighter rock.

  The inner core also consists of iron and nickel though it is solid, even at 6200⁰C. The pressure is so great that the metal is not able to expand and melt.
• how thick is the crust

  0-100km
• what causes continental drift


  convection currents
• how do convection currents work

  heat produced by radioactive decay, causes a current of less dense rock to rise.

  when it hits the crust it is forced sideways as it cannot break through the crust (although some does creating mid ocean ridges)

  the moving magma drags plates along with it

  the magma then cools and sinks back to the core repeating the process and creating slab pull.
• how does continental drift occur

  The heat from the core (concentrations of radioactive material) causes the lower mantle to become less dense and rise towards to the crust.

  
  

  Just below the crust the magma cools and spreads sideways. The plates move along with this convection current.

  
  

  As magma escapes through the cracks in the crust it forces the plates apart. This is called ridge push.

  
  

  The cooler magma starts to sink back to the mantle. As it sinks it drags oceanic crust down into the mantle. This is called slab pull.

  
  

  The combination of ridge push and slab pull causes plates to move slowly, and continental drift to occur.
• 3 types of plate margin

  divergent

  convergent

  conservative
• what do divergent plate margins create

  Sheila volcanoes, fissures, rift valleys and mid ocean ridges
• what happens on a divergent plate margin

  as the plates stretch apart the crust becomes thiner

  fissures develop parallel to the plate margin.

  land may become unsupported and fall creating rift valleys

  magma erupts beneath fissures creating shield volcanoes

  under water the lava cools quickly creating mid ocean ridges
• what happens when a oceanic and continental plate collide

  the denser (oceanic) plate will be subducted
• What happens at a subduction zone?

  as the denser plate is dragged down into the mantel it creates great heat through friction which melts part of the plate creating a magma chamber under high pressure
• what happens over time in the subduction zone

  Built up magma inside the magma chamber burst through the mountainside due to the high pressure.
• what hazards occur at convergent plate margins

  earthquakes occur due to high pressure building up and eventually suddenly moving.
• example of convergent plate boundary between two oceanic plates


  Japan was created by an offshore subduction zone as the less dense plate was dragged into the mantle creating volcanoes which over time created an Island arc
• what happens to crust at a conservative plate margin


  its neither created nor destroyed it simply moves along side each other
• what is the biggest risk from conservative plate margins and why

  earthquakes. friction between the plates leads to pressure building and sudden quick movements causing earthquakes.
• what causes hot spots

  extremely hot areas of mantle flow up to the crust and melt their way through and volcanic eruptions create new land over time.
• how do Plates move

  convection currents, ridge push and slab pull.
• what's the difference between the lithosphere and asthenosphere

  the lithosphere is rigid and floats on top of the more viscous asthenosphere
• which type of crust is thiner and younger

  oceanic crust although its denser
• what causes convection currents

  a concentration of radioactive material
• What is ridge push? (gravitational sliding)


  where rising magma pushes up in between two plates and forces them to rise.

  when the magma subsequently cools the plates slide down due to gravity pulling the rest of the plate with it

  
• where does ridge push occur?

  divergent plate boundaries
• Where does slab pull occur?

  convergent plate boundaries
• what can happen as a result of two oceanic plates diverging?

  what's an example

  a mid ocean ridge forms, eg the mid Atlantic ridge where the North American and Eurasian plates diverge
• what can happen as a result of two continental plates diverging?


  rift valley, eg East African rift valley.
• what happens when two continental plates collide

  significant earthquakes and mountains although no magma build up
• what happens when two oceanic plates collide


  the older, denser plate is subjected