Section A - Natural Hazards

• Natural hazard - An event caused by the environment that results in damage to people or property
• A natural hazard becomes a natural disaster when it has caused:

  • 10 deaths
  • 100 injuries
  • $16 million loss
• A natural event is an event that is caused by a natural phenomenon, such as a volcanic eruption or a hurricane. It becomes a hazard when it causes damage to people or property
• Atmospheric hazard - related to weather and climate
• Geological / Tectonic hazard - related to the Earth's crust
• Hydrological hazard - related to water bodies
• Hazard risk - the probability of a population being affected by a natural event
• Factors increasing hazard risk:

  • Urbanisation - 50% live in cities, causing informal settlements increase. These are riskier areas because of poorly built houses
• Factors increasing hazard risk:

  • Climate change - global warming increases energy in atmosphere making storms more intense. Increasing rain and sea levels increase flood risk / severity
• Factors increasing hazard risk:

  • Poverty - shortage of housing forces people to live in informal settlements which are more easily destroyed. LICs can't afford infrastructure or hazard defences
• Factors increasing hazard risk:

  • Agriculture - farmers will live on floodplains or volcanoes because alluvium / Ash makes soil more fertile
• Why people live in hazardous areas:

  • Tourism creates jobs (Etna)
  • Ash creates fertile farmland (Agung)
  • Geothermal energy heating groundwater provides renewable energy (New Zealand)
• Earth's layers:

  • Crust (solid): 8-40km
  • Mantle (magma): 2900km
  • Inner core (solid): 1300km
  • Outer core (liquid): 2250km
• Inner core is made from iron and nickel. It is in a state of radioactive decay
• Plates:

  • Earth's crust is made from them
  • Meeting points are plate boundaries/margins
• Plate movement evidence:

  • Match in shape
  • Similar rock patterns
  • Similar fossils
• Continental drift - the movement of tectonic plates and continents
• Oceanic crust:

  • 5-10km thick
  • More dense
  • Younger
  • Can be destroyed at margins
• Continental crust:

  • 30-50km thick
  • Less dense
  • Older
  • Not destroyed at margins
• Theories for plate movement:

  • Convection currents
  • Ridge push
  • Slab pull
• Convection currents:

  1. Heat from core makes magma lighter (it rises)
  2. Magma starts to cool down (it solidifies)
  3. Cooler magma is forced sideways at the crust by fresh. The solid magma creates friction and moves the crust
  4. Dense, solid magma sinks back towards core
  5. It is heated by core to become lighter and rise
• Ridge push:

  1. Fresh magma rises to the surface at a constructive margin
  2. The two plates are forced apart and up, away from the ridge, by an injection of new magma
  3. The mid-ocean ridge is elevated higher than the ocean floor, so gravity causes the plate to move down and away
• Slab pull:

  1. At destructive plate margins, the denser plate subducts under the lighter one
  2. The denser plate is dragged into the mantle due to gravity
• Volcanoes:

  • 500 active
  • Can be active, dormant, or extinct
  • Most are found on plate margins
  • 50% are found on the ring of fire
  • Also found on Mid-atlantic ridge
  • Pacific plates are moving the faster
• Earthquake:

  • A sudden or violent period of ground shaking
  • Caused by a sudden movement of rocks in the crust due to a release of pressure/friction
  • Over 20,000 per year
• Plate margins:

  • Constructive
  • Destructive
  • Conservative
  • Collision
• Constructive:

  • Two oceanic plates move apart and magma fills in the gap created
  • Volcanoes due to magma and pressure
  • (Rarely) earthquakes due to friction
• Destructive:

  • Plates (one oceanic and one destructive) move together.
  • Oceanic plate subducts
  • Volcanoes due to pressure from magma
  • Earthquakes due to plate friction
• Conservative:

  • Plates move alongside eachother in the same or opposite directions
  • Earthquakes due to friction
  • No volcanoes
• Collision:

  • Two of the same plates move towards eachother.
  • Neither subduct and both are forced up
  • Earthquakes due to friction
  • No volcanoes
• Volcanic eruptions are easier to predict than earthquakes bacuse they have more warning signs that appear further in advance
• Volcanic eruption warning signs:

  • Earthquakes
  • Ground deformation due to changing gas and pressure
  • Gas releases (sulphur)
• Measuring warning signs:

  • Seismicity - earthquakes
  • Laser beams to measure shapes - ground deformations
  • Gas/hydrology - gas releases
• Earthquake resistant buildings:

  • Cross-bracing to reinforce walls
  • Automatic shutters over windows, to stop glass falling
  • Underground shock absorbers
• Hazard maps - show the most at-risk areas of land. Used to decide land use
• Volcanoes are hard to protect against due to scale. Strategies include concrete walls and explosives to divert lava
• Factors needed for a tropical storm:

  • Sea temperature above 26.5°C
  • Sea depth at least 75m
  • 5-15m North or South of equator (coriolis effect)
  • 120+km/h wind speeds
  • Unstable conditions
• Coriolis effect:

  • Anti-clockwise in Northern hemisphere
  • Clockwise in Southern hemisphere
• Landfall - where a tropical storm meets the land. It will weaken and die out because there is less warm water and more friction with the land
• Formation of storms:

  1. Warm water vapour rises up
  2. It condenses, releasing latent heat which powers the storm
  3. More air condenses
  4. Coriolis effect begins
  5. Storm develops and eye
  6. Smaller storms join to make one large one
  7. Storm carried by prevailing winds and gains energy
  8. As it hits land it loses energy and weakens. May gain energy again later