geography section A

• Natural Hazard


  A natural process which can cause death, injury, disruption to humans or destroy property and possessions
• Natural Disaster


  A natural Hazard that has already happened
• Types of natural hazards

  • Geological hazards
  • Meteorological hazards
• Geological hazards


  • Caused by the land and tectonic processes
• Geological hazards


  • Volcanoes
  • Earthquakes
  • Landslides
• Meteorological hazards


  • Caused by weather and climate
• Meteorological hazards


  • Tropical storms
• Factors affecting hazard risk

  • Human factors: Population, Income level, Ability to cope
  • Natural factors: Type of hazard, Frequency and magnitude, Physical geography
• Primary effects of natural hazards

  • Building and Road destruction
  • Deaths and injuries
  • Crop and Water Supplies being damaged or contaminated
  • Electricity cables, gas pipes and communication networks being damaged
• Secondary effects of natural hazards

  • Initial hazards triggering other hazards
  • Emergency aid unable to get through
  • Lack of clean water and sanitation causing diseases
  • Country's economy being weakened
• Immediate responses to natural hazards

  • Evacuating people
  • Treating the injured
  • Rescuing people
  • Giving temporary food and water supplies
  • Foreign aid from other countries
• Long-term responses to natural hazards


  • Repairing houses
  • Repairing buildings
  • Repairing roads
  • Improving forecasting, monitoring and evacuation plans
  • Promoting tourism to boost economy
• Tectonic plates


  Random jagged shapes that the Earth's outer layer (crust) is divided into
• Plate margins/boundaries


  Where the tectonic plates meet
• Types of plate margins

  • Destructive
  • Constructive
  • Conservative
• Destructive plate margins


  • Plates collide towards each other
• Constructive plate margins


  • Plates pull apart
• Conservative plate margins


  • Plates move side by side in different directions or at different speeds
• Volcanoes are only formed at destructive and constructive plate margins
• Formation of destructive volcanoes

  1. Oceanic and continental plates collide

  2. Denser oceanic plate sinks/subducts beneath continental plate

  3. Heat and pressure melts oceanic plate into magma

  4. Magma rises back up through cracks in crust (vents)

  5. Forms destructive/composite volcanoes
• Formation of constructive volcanoes

  1. Plates pull apart, creating a gap

  2. Magma rises up and fills the gap

  3. Forms shield volcano
• Tectonic plates


  Random shapes that the Earth's outer layer (the crust) is divided into
• Plate margins/boundaries


  Where the tectonic plates meet
• Tectonic plates are constantly moving
• Tectonic plates get stuck

  When they finally move, they release a lot of energy in the form of seismic waves, causing an earthquake
• Earthquakes are unpredictable
• Focus


  The point in the Earth where the earthquake starts, normally in the mantle
• Epicenter


  The point directly above the focus on the Earth's surface
• Seismic waves


  Vibrations from the earthquake, strongest near the epicenter and weakest further away
• Moment magnitude scale


  Used to measure earthquakes, from 1 to 10
• Earthquake magnitude ≤ 6


  May cause slight damage to buildings
• Earthquake magnitude ≥ 7


  Will cause major damage and death
• The moment magnitude scale is logarithmic, so a 7 magnitude earthquake is 10 times bigger than a 6 magnitude earthquake
• Global atmospheric circulation


  The transfer of heat from the equator to the poles by the movement of air
• Why air moves


  1. Difference in air pressure

  2. High pressure - cool air descends

  3. Low pressure - warm air ascends
• How global atmospheric circulation works

  1. Equator is hottest part due to tilt

  2. Air rises at equator due to warming, creating low pressure and rainfall

  3. Air reaches edge of atmosphere, travels north and south, becomes colder and denser, descends creating high pressure and dry conditions at 30 degrees north and south

  4. Cycle repeats with air rising at 60 degrees north and south, descending at 90 degrees north and south
• Hadley cells


  • Air rises at equator, separates and moves north and south, sinks at 30 degrees north and south
  • Creates trade winds flowing towards equator
• Ferrel cells


  • Air pulled towards poles, meets cold air from poles, warm air rises creating low pressure and unstable weather
• Polar cells


  • Cold air sinks at poles, flows towards lower latitudes, meets warm tropical air and rises
• Global atmospheric circulation


  Creates winds across the planet, leading to areas of high rainfall like tropical rainforests and areas of dry air like deserts