tec hazards

• Convergent plate boundaries


  • Oceanic continental
  • Oceanic crust is destroyed at subduction zone
  • Pressure build up and eventually slip past each other resulting in an earthquake
• Conservative plate boundaries


  • Oceanic-oceanic or continental-continental or oceaninc-continental
  • Plates move past each other horizontally
  • Friction and pressure build up and eventually slip past each other resulting in an earthquake and formation of composite volcanoes
• Divergent plate boundaries


  • Two plates move past each other (diverge)
  • Convection currents beneath surface force plates apart
  • Magma rises and cools on the surface forming shield volcanoes
• Tectonic hazards


  • Earthquake
  • Volcanic eruption
  • Tsunami
• Tectonic hazards happen at divergent, convergent or conservative plate boundaries
• Some areas are more at risk than others
• Intra-Plate Earthquakes and Volcanoes

  • Mantle plumes create areas of weakness known as hotspots and result in volcanoes
  • Isolated plumes of convecting heat (mantle plumes) rise towards the surface generating basaltic volcanoes
  • Plate movement over time produces a chain of volcanic islands, with extinct ones furthest from the plume location
  • Can usually occur at ancient fault lines being reactivated by tectonic stresses
  • Zones of weakness are created as plates move and stresses increase
• Wegener's Continental Drift


  Continents had once been joined together as supercontinents
• Gravitational sliding


  Elevated altitudes of oceanic crust at ridges at divergent plate boundaries – create a 'slope' down which oceanic plates slide
• Slab pull


  At convergent boundaries, the high-density ocean floor is being dragged down by a downward gravitational force
• Sea floor spreading


  Earth's magnetic field proves that new crust is created by the process of seafloor spreading at mid-ocean ridges
• Holmes' Hypothesis

  The Earth's magnetic field proves that a new crust is created by the process of seafloor spreading at mid-ocean ridges
• Divergent plate margins


  • Volcanic eruptions are basaltic and produce low viscosity lava
  • Earthquakes are low magnitude and shallow focus
  • tectonic plates move away from each other
• Convergent plate margins


  • Deep-sea trenches and fold mountain ranges often form
  • Volcanic activity is often violent due to the high viscosity of lava
  • Earthquakes are high magnitude, deep-focus
  • When two plates come together
• Conservative plate margins


  • No volcanic activity
  • Earthquakes are high magnitude, shallow-focus
  • two crustal plates slide past each other
• Focus


  Where the pressure is released underground and where the energy radiates out from. This is the place with the strongest waves that cause the most damage.
• Epicentre


  The point directly above the centre of the earthquake on the earth's surface
• Seismic waves


  Energy released from the focus in shock waves
• Shallow-focus earthquakes


  • Focus is 0-70km under the Earth's surface
• Deep-focus earthquakes


  • Focus is 70-700km under the Earth's surface
  • Caused by previously subducted crust moving towards the core, heating up or decomposing
  • Less damaging than shallow-focus because the shock waves have to travel further
• Underwater earthquakes


  • Move the seabed, which causes water to get displaced
  • If enough water is displaced, tsunamis can happen
  • The deeper the focus, the bigger the tsunami
  • Waves travel fast in deep water, and so tsunamis can strike shores with little warning
• 1. primary waves

  • first waves released when tectonic energy is released
  • Fastest waves but cause the least damage
• secondary waves make the ground shake violently
• Love waves

  • create significant damage, including crustal fracturing
  • Only travel across the surface and have a large amplitude
• Primary hazards of earthquakes

  • Ground shaking, which can range in duration and severity based on the magnitude of the earthquake and the distance from the epicentre
  • The earth may visibly separate
• Secondary hazards of earthquakes

  • Large landslides
  • Tsunamis from submarine earthquakes
• Primary hazards of volcanoes

  • Ash fall
  • Volcanic gases
  • Pyroclastic flows
  • Lava flows
• Secondary hazards of volcanoes

  • Lahars
  • Flooding from glacial or ice cap melt
• Causes of tsunamis


  • Most are generated by submarine earthquakes at subduction zones
  • The sea bed is displaced vertically (up or down) - this motion displaces a large volume of water in the ocean column which then moves outwards from the point of displacement
• Risk


  The probability of a hazard happening and creating a loss of lives and/or livelihoods
• Vulnerability


  The risk of exposure to hazards combined with an inability to cope with them
• Resilience


  The degree to which a population or environment can absorb a hazardous event and stay organised and functioning
• Features that increase a population's resilience

  • Having emergency evacuation, rescue and relief systems in place
  • Helping each other to reduce the numbers affected
  • Having a hazard-resistant design or land-use planning to reduce the numbers at risk
• Pressure and Release (PAR) model


  Shows the connections between the nature of a hazard and its wider context, including socio-economic factors and the specific nature of the hazard
• Impacts of hazards

  • Social impacts (deaths, injury, health, psychological)
  • Economic impacts (loss of property, businesses, infrastructure, opportunities)
  • Environmental impacts (damage or destruction of ecosystems)
• Moment Magnitude Scale (MMS)


  Measures the amount of energy released in an earthquake, from 1 to 10 with higher numbers meaning greater magnitude
• Mercalli scale


  Measures the intensity of shaking from earthquakes on a scale of 1 to 12
• Volcanic Explosivity Index (VEI)


  Measures the magnitude of volcanic eruptions based on the volume, duration and column height
• Hazard profiles


  Summarise the physical processes shared by all hazards so that decision-makers can determine which areas are most at risk
• Human Development Index (HDI)


  Measures inequality of access to education, housing, healthcare and income, which influence vulnerability and resilience