geography - hazards A level

• Geographic hazards refer to natural processes or features that may cause harm to human society, infrastructure or the environment.
• Hotspots occur when molten rock from deep within the Earth's mantle reaches the surface through cracks in the lithosphere.
• Disaster refers to an extreme event which causes significant loss of life, injury, economic disruption, social upheaval, environmental degradation etc.
• Hazard is defined as any event with the potential to cause damage
• Dregg’s Model

  Known as a disaster once hazard crosses with a vulnerable population (dese pop/ poverty)

  10 deaths/ 100 injured/ International Assistance Required
• Structure of earth

  1. Crust (Oceanic/ continental)

  2.Lithosphere

  3.Asthenosphere

  4.Mesosphere

  5.Mantle

  6.Outer core

  7.Inner core
• Crustal evolution theory

  1. Francis Bacon – Map jigsaw

  2.Alfred Wegener – Pangea and biological/ geological evidence

  3.Sea floor spreading – polarity evidence either side of mid Atlantic ridge/Subduction – as earth not growing oceanic crust must be being destroyed

  5. Convection currents – plates are pulled apart/ push together due to rising and sinking convection cells caused by earth internal heat in the core

  6. Gravity – ridge push/ gravitational sliding

  7. Slab pull
• Constructive:

  Oceanic crust being pulled apart/ causing sea floor spreading.

  Movement caused by rising convection currents in the asthenosphere driven by heat from the core and by ridge push/ gravitational sliding which is the force of gravity also pulling the plates apart.
• Destructive

  Oceanic and continental crust being pushed together. This causes the movement of subduction as the denser oceanic crust sinks back into the asthenosphere as the plates are forced together.

  Movement caused by sinking convection currents in the asthenosphere driven by loss of energy as away from heat from the core and slab pull which is the downward force of gravity on the sinking plate.
• Conservative:

  Two slabs of crust sliding past each other either in the same or opposing direction.

  Movement caused due to the push and pull movement of the other surrounding plates. Not directly linked to sea floor spread or subduction and convection currents.
• Hot spots/ plumes

  Slabs of crust are constantly moving due to convection currents.

  When crust moves over a hot spot/ plume which is caused by a hot section of the core/ mantle it will cause a chain of volcanoes in the crust directly above the hot spot.
• Ocean Ridges – Constructive Boundaries

  • up lifted piece of land
  • forms when plates move apart in oceanic areas
  • rising convection currents lifts/pushes land up
  • gravity takes hold and pushes the ridge apart
  • space between the plates is filled with basaltic lava
  • e.g. mid Atlantic ridge
• Rift Valleys – Constructive Boundaries

  • valleys form when plates move apart (continental)
  • as plates pull apart the crust will get thinner and drop down in sections as weakening thick continental crust - areas of crust drop down between parallel faults to form the valley
  • cracks form - magma can rise to the surface
  • an area between 2 parallel rift valleys forms an upstanding block known as a horst
  • e.g. African Rift Valley