Hazards content

• Natural Hazard


  A natural process which could cause death, injury or disruption to humans, or destroy property and possessions
• 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 (eg, a drought in an uninhabited desert or an avalanche in Antarctica)
• Main Types of Natural Hazard

  • Geological Hazards
  • Meteorological Hazards
• Geological Hazards


  • Caused by land and tectonic processes
  • Include volcanoes and earthquakes, landslides and avalanches
• Meteorological Hazards


  • Caused by weather and climate
  • Examples include storms, floods, droughts, heatwaves and cold spells
• Hazard Risk


  The probability of people being affected by a hazard in a particular area
• Factors affecting Hazard Risk


  • The number of people in an area exposed to natural hazards
  • The capacity of a population to cope with an extreme event
  • The nature of the hazard(type/frequency/magnitude)
• Higher income countries (HICs)


  Better able to cope with flooding because they can afford to build flood defences and evacuate people
• Earthquakes can also trigger landslides, tsunamis, and volcanic eruptions.
• Volcanoes are mountains that have been formed from solidified lava or ash ejected during previous eruptions.
• Tsunami is a series of large waves caused by underwater earthquakes, volcanic eruptions, or other disturbances on the ocean floor.
• Landslide is a sudden downward movement of rock, debris, or soil due to gravity.
• Avalanche is a rapid flow of snow down a mountain slope triggered by gravity.
• Natural Hazards


  Have both effects and responses
• Natural Hazards Have Primary and Secondary Effects
• Primary effects of natural disasters

  1. Buildings and roads are destroyed

  2. People are injured or killed

  3. Crops and water supplies can be damaged or contaminated

  4. Electricity cables, gas pipes and communication networks can be damaged, cutting off supplies
• Secondary effects of natural disasters

  1. The initial hazard can trigger other hazards

  2. Aid and emergency vehicles can't get through because of blocked roads or bridges

  3. Shortage of clean water and lack of proper sanitation makes it easier for disease to spread

  4. Food shortages can occur

  5. The country's economy can be weakened
• Immediate Responses


  • Evacuate people
  • Treat the injured and rescue anyone cut off by damage
  • Recover dead bodies to prevent disease spreading
  • Provide temporary supplies of electricity and gas
  • Provide food, drink and shelter
  • Foreign governments or charities may send aid
• Long-Term Responses


  • Repair homes or rehouse people
  • Repair or rebuild buildings, roads, railways and bridges
  • Reconnect broken electricity, water, gas and communication connections
  • Improve forecasting, monitoring and evacuation plans
  • Improve building regulations
  • Boost economic recovery
• Tectonic Plates

  Huge floating plates that are constantly moving and make up the Earth's surface
• The Earth's Surface is Separated into Tectonic Plates

  1. The Earth's crust (its outer layer) is divided into slabs called tectonic plates that float on the mantle (a layer of semi-molten rock)

  2. Plates are made of 2 types of crust: Continental crust is thicker (30-50 km) and less dense, Oceanic crust is thinner (5-10 km) and more dense

  3. The plates are moving because of convection currents in the mantle

  4. The places where plates meet are called plate margins or plate boundaries
• Types of Plate Margin

  • Destructive Margins
  • Constructive Margins
  • Conservative Margins
• Destructive Margins

  • Where two plates are moving towards each other
  • Where an oceanic plate meets a continental plate, the denser oceanic plate is subducted (forced down into the mantle and destroyed), creating gas-rich magma. Volcanoes and ocean trenches occur here
  • Where continental plates meet, the ground is folded upwards, creating fold mountains
• Destructive Margin Example

  • Along the west coast of South America, the oceanic Nazca plate is being subducted beneath the continental South American plate, creating the Atacama Trench
• Constructive Margins

  • Where two plates are moving away from each other
  • Magma rises from the mantle to fill the gap and cools, creating new crust
• Constructive Margin Example

  • The movement of the Eurasian plate and the North American plate away from one another is forming the mid-Atlantic ridge
• Conservative Margins

  • Where two plates are moving sideways past each other, or are moving in the same direction but at different speeds
  • No new crust is created or destroyed
• Conservative Margin Example

  • At the San Andreas Fault the Pacific plate is moving in the same direction as the North American plate but it is moving faster
• Where plates meet, volcanoes and earthquakes occur
• Volcanoes

  Occur at Destructive and Constructive Plate Margins
• Volcanoes at Destructive Margins

  1. Denser oceanic plate moves down into the mantle, where it melts

  2. A pool of magma forms

  3. Magma rises through cracks in the crust called vents

  4. Magma (called lava when it reaches the surface) erupts, forming a volcano
• Volcanoes at Constructive Margins

  Magma rises up into the gap created by the plates moving apart, forming a volcano
• Some volcanoes

  Form over parts of the mantle that are really hot (called hotspots), e.g. in Hawaii
• Volcano eruptions

  • Emit lava and gases
  • Some volcanoes emit lots of ash, which can cover land, block out the sun and form pyroclastic flows (super-heated currents of gas, ash and rock)
• Earthquakes

  Occur at All Three Types of Plate Margin
• Earthquakes at Destructive Margins

  Tension builds when one plate gets stuck as it pushes against the other
• Earthquakes at Constructive Margins

  Tension builds along cracks in the plates as they move away from each other
• Earthquake occurrence

  1. Plates eventually jerk past each other, sending out shock waves

  2. Shock waves spread out from the focus (the point in the Earth where the earthquake originated)

  3. Waves are strongest near the focus and cause more damage
• Epicentre

  The point on the Earth's surface directly above the focus