Natural Hazards and Tectonic Hazards

• Natural hazard

  an extreme natural event that threatens property and human life
• Types of natural hazards:

  • earthquakes
  • volcanoes
  • tsunamis
  • tropical storms
  • droughts
  • wildfires
  • tornadoes
  • floods
• Factors that affect the risks that hazards pose:

  • wealth
  • population density
  • geographical location
• Wealth


  how rich or poor a country is will affect how it prepares for a hazard, and how it is able to cope with the effects of a hazard
• Population density


  areas that have high population densities are more likely to be severely impacted
• Geographical location


  the location of a place influences the risks that hazards pose
• The Earth's surface is divided into different sections called tectonic plates
• Types of tectonic hazards:

  • Volcanoes
  • Earthquakes
• Tectonic hazards

  Natural hazards that occur at plate margins
• Plate margins

  where two tectonic plates meet
• Places near plate margins are more at risk of tectonic hazards than others
• Tectonic plate can move apart, towards each other and side by side
• The Earth's four layers:

  • crust
  • mantle
  • outer core
  • inner core
• Crust

  the surface of the planet and is divided into tectonic plates - the two types of crust are oceanic crust, which is heavier and denser, and continental crust
• Mantle

  molten rock
• Outer core

  liquid iron and nickel
• Inner core

  solid iron and nickel
• Two theories for why the Earth's plates move:

  • convection currents in the mantle move the plates
  • ridge push/ slab pull - heavier oceanic crust sinks into the mantle, pulling the plate downwards
• Three types of plate margins:

  • destructive
  • constructive
  • conservative
• Destructive plate margins:

  • an oceanic plate moves towards a continental plate
  • the denser oceanic plate is subducted beneath the continental plate
  • friction between the plates as they move causes earthquakes
  • the oceanic plate melts in the mantle and mixes with sea water
  • this liquid rises up through cracks in the mantle as a volcanic eruption
• Hazards of destructive plate margins:

  • powerful earthquakes
  • violent composite volcanoes
• Constructive plate margins:

  • two plates move apart from each other
  • this creates a gap in the Earth's crust
  • magma from the mantle rises up to fill this gap and a volcanic eruption occurs
  • small earthquakes also happen due to the movement of the magma
• Hazards of constructive plate margins:

  • gentle earthquakes
  • gently sloping shield volcanoes
• Conservative plate margins:

  • two plates slide past each other
  • as they move they get caught on each other
  • pressure builds up (friction) and is released as an earthquake when the plates suddenly jolt free
• Hazards of conservative plate margins:

  • earthquakes
• what is the focus of an earthquake?

  the point in the Earth's crust where the pressure is released
• Seismic waves

  the energy released in an earthquake
• What is the epicentre of an earthquake?

  the point on the Earth's surface directly above the focus