The challenge of natural hazards

• Natural Hazard


  A threat to people or property
• Natural Disaster


  A natural hazard that has actually happened
• Extreme events which do not pose any threat to human activity are not counted as hazards, e.g. a drought in an uninhabited desert or an avalanche in Antarctica
• Two Main Types of Natural Hazard

  • Geological Hazards
  • Meteorological Hazards
• Geological Hazards


  • Caused by land and tectonic processes, e.g. volcanoes, earthquakes, landslides, avalanches
• Meteorological Hazards


  • Caused by weather and climate, e.g. tropical storms, extreme weather
• Hazard Risk


  The probability of people being affected by a hazard in a particular area
• Factors that can affect hazard risk


  • Vulnerability
  • Nature of Natural Hazards
  • Capacity to Cope
• Vulnerability


  The more people that are in an area exposed to natural hazards, the greater the probability they will be affected
• Vulnerability


  • High population density on a flood plain like much of Bangladesh
  • City at the base of a volcano like Naples, Italy
• Capacity to Cope


  The better a population can cope with an extreme event, the lower the risk of them being severely affected
• Capacity to Cope


  • Higher income countries (HICs) can afford to build flood defences and evacuate people
• Factors affecting the nature of natural hazards


  • Type
  • Frequency
  • Magnitude
• Type


  The risk from some hazards is greater than others, e.g. tropical storms can be predicted and monitored, but earthquakes happen suddenly with no warning
• Frequency


  Natural hazards that occur more often may carry a higher risk
• Magnitude


  More severe natural hazards tend to have the greatest effects
• Magnitude


  • A magnitude 2.0 earthquake in Japan in 2011 killed over 15,000 people, whereas a magnitude 6.3 earthquake in L'Aquila, Italy in 2009 killed around 300 people
• Natural hazards have primary and secondary effects
• Primary Effects


  • Buildings and roads destroyed
  • People injured or killed
  • Crops and water supplies damaged or contaminated
  • Electricity, gas, and communication networks damaged
• Secondary Effects


  • Hazards triggering other hazards
  • Aid and emergency vehicles unable to get through
  • Spread of disease due to lack of clean water and sanitation
  • Food shortages
  • Economic damage
• Immediate Responses


  • Evacuate people
  • Treat injured and rescue anyone cut off
  • Recover dead bodies
  • Provide temporary supplies of electricity, gas, food, drink, and shelter
  • Foreign aid
• Long-Term Responses


  • Repair homes and buildings
  • Reconnect utilities
  • Improve forecasting, monitoring, and evacuation plans
  • Improve building regulations
  • Boost economic recovery
• The Earth's surface is divided into tectonic plates that are constantly moving
• Types of Crust


  • Continental crust (thicker, less dense)
  • Oceanic crust (thinner, more dense)
• Plate Margins


  The places where plates meet
• Types of Plate Margins


  • Destructive
  • Conservative
  • Constructive
• Destructive Margins


  • Two plates moving towards each other, with the denser oceanic plate being subducted and creating volcanoes and ocean trenches
• Conservative Margins


  • Two plates moving sideways past each other or in the same direction at different speeds, with no creation or destruction of crust
• Constructive Margins


  • Two plates moving away from each other, with magma rising to fill the gap and create new crust
• Volcanoes occur at destructive and constructive plate margins
• Volcano Formation at Destructive Margins


  1. Denser oceanic plate subducted into mantle

  2. Melts to form magma pool

  3. Magma rises through cracks and erupts as lava
• Volcano Formation at Constructive Margins


  Magma rises up into gap created by plates moving apart
• Volcanoes can also form over hot spots in the mantle, e.g. Hawaii
• Volcanic Eruption Effects


  • Lava emissions
  • Ash emissions that can block out the sun and form pyroclastic flows
• Earthquakes occur at all three types of plate margin
• Earthquake Formation at Destructive Margins


  Tension builds as one plate gets stuck moving past the other
• Earthquake Formation at Constructive Margins


  Tension builds along cracks in plates as they move away from each other
• Earthquake Formation at Conservative Margins


  Tension builds as plates grinding past each other get stuck
• The plates eventually jerk past each other, sending out shock waves which are the earthquake
• Focus


  The point in the Earth where the earthquake starts