Geography

• Natural hazards


  Sudden severe events which make the natural environment difficult to manage
• Natural hazards are extreme natural events that can cause loss of life, extreme damage to property and disrupt human activities
• Disaster


  When natural hazards cause high levels of death, injury, damage or disruption to human life
• Types of natural hazards

  • Floods
  • Tropical storms
  • Earthquakes
  • Droughts
• Categories of natural hazards

  • Atmospheric
  • Hydrological
  • Geological/Geomorphological
  • Biological
• Hazard risk


  The chance of being affected by a natural hazard
• People live in risky areas because they have little choice as to where to live
• Factors affecting risk


  • Urbanisation
  • Poverty
  • Farming
  • Climate change
• Tectonic plates


  Slabs that the Earth's crust is divided into

  
• Types of crust


  • Oceanic
  • Continental

  
• Oceanic crust


  • 5-10 km thick, denser (heavier), younger and can be destroyed

  
• Continental crust


  • 30-50 km thick, less dense, older and can never be destroyed

  
• Plate movement


  1. Driven by convection currents

  2. Earth's core heats mantle

  3. Heated magma rises, cools and sinks

  4. Convection currents drag plates along

  
• Plate margins


  • Destructive
  • Conservative
  • Constructive
• Destructive plate margin


  Two plates moving towards one another, denser oceanic plate subducted into mantle

  
• Conservative plate margin


  Two plates moving alongside each other, tension builds up and is released as an earthquake
• Constructive plate margin


  Two plates moving apart, magma rises up to fill the gap and forms new crust
• Earthquake


  A sudden, violent period of ground-shaking, caused by friction and sticking between plates

  
• Volcano


  Large, often cone-shaped landforms, formed over long periods by several eruptions, occur at plate margins and hot spots

  
• The theory of continental drift was proposed by Alfred Wegener
• Before Wegener, it was thought mountains formed as the Earth cooled and contracted
• Wegener's theory


  Mountains formed when the edge of a drifting continent collided with another, causing it to crumple and fold
• Evidence for continental drift


  • Match in shape between east coast of South America and west coast of Africa
  • Similar patterns of rocks on both sides of the Atlantic
  • Similar fossils on both sides of the Atlantic
• Focus


  The point inside the Earth's crust where the earthquake originates from

  
• Epicentre


  The point on the Earth's surface directly above the focus
• Richter scale


  Measures the magnitude of an earthquake, logarithmic scale from 1-10

  
• Effects of earthquakes


  • Primary effects (ground shaking)
  • Secondary effects (fires, landslides)
  • Immediate responses (emergency care)
  • Long-term responses (reconstruction)

  
• Reasons why people live at risk from tectonic hazards

  • Poor people have no choice
  • Earthquakes and volcanic eruptions are rare
  • Earthquake-resistant building designs
  • Effective monitoring and warning systems
  • Plate margins coincide with favourable settlement areas
  • Lack of experience or knowledge of risks
  • Volcanoes can bring benefits
• Monitoring techniques for volcanoes

  • Remote sensing
  • Seismicity
  • Ground deformation

  
• Earthquakes generally occur without warning, but some precursor events can occur