Natural Hazards


What is a natural hazard?

  • A natural event becomes a natural hazard when it has a social impact (impact on people and human activities).
  • A natural event and a vulnerable population creates a natural disaster.
  • Hazard risk is the chance or probability of being affected by a natural event.
  • The three types of Hazards are:
    • Category A: Atmospheric Hazards
    • Category B: Geological Hazards
    • Category C: Flooding
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Examples of Category A Hazards

  • Storm/Rain
  • Lightning
  • Wild Fire/Drought
  • Blizzard/Snow
  • Hurricane
  • Tornado
  • Wind
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Examples of Category B Hazards

  • Volcano
  • Landslide
  • Mudslide
  • Avalanche
  • Earthquake
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Factors affecting a hazard risk

  • Location
  • Level of Development
  • Time of year/day
  • Population distribution and density
  • Farming
  • Hazard managment
  • Frequency
  • Natural factors
  • Magnitude
  • Urbanisation
  • Education
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Earth's Layers

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Inner Core

  • Made of nickel and iron.
  • 6000 - 7000 degrees celcius.
  • Solid due to the intense pressures in the centre of the Earth.
  • All the other layers are heated by the core (so it gets cooler towards the surface).
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Outer Core

  • Made of nickel and iron.
  • Liquid Layer.
  • Between 3000 - 6000 degrees celcius.
  • Approximately 2000 km deep.
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The Mantle

  • This is the thickest layer within the Earth
  • Forms about half the Earth.
  • High Temperatures in this layer - up to 1300 degrees celcius.
  • Upper mantle is hard but the rock below it is soft and runny in places (moving as slowly as your fingernails grow).
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  • Thin skin of rock around the Earth.
  • 5km - 8km thick.
  • Broken into plates.
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Continental plates

  • Older - most over 1500 million years old.
  • Less dense.
  • Cannot sink.
  • Cannot be renewed or destroyed.
  • Granite.
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Oceanic plates

  • Newer - most under 200 million years old.
  • Denser.
  • Can sink.
  • Can be renewed and destroyed.
  • Basalt.
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Formation of the Continents

  • 225 million years ago, all the land masses were one land mass called Pangaea.
  • Over time the land masses moved apart to create the continents we have today.
  • India started south of the equator but moved up and collided with Asia to become part of Asia.
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Plate tectonics theory evidence

  • A scientist called Alfred Wegner first suggested the idea of continental drift.
  • Study of fossils: fossils of the same creatures were found in different continents.
  • Pattern of rocks: similar patterns of rock layers, in some places they are exactly the same.
  • Shape of continets fit like a jigsaw.
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Convection Currents

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How do plates move?

  • Plates move on a bed of molten lava.
  • Convection currents carry heat  from the hot inner mantle to the cooler outer mantle.
  • The hot rock rises, cools then sinks back to the core.
  • The hot core is driving the plates as it sets up convection currents in the mantle.
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Plate Boundaries

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Factors increasing the risk from Natural Hazards

  • Urbanisation - Over 50 percent of the world's population live in cities. Some of the world's largest cities (e.g. Tokyo, Istanbul and Los Angles) are at risk from earthquakes. Densely populated urban areas are at great risk from natural events.
  • Poverty - In poorer parts of the world poverty may force people to live in areas at risk. In Lima and Carcas a shortage of housing has lead to people building on unstable slope prone to floods.
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Factors increasing the risk from Natural Hazards

  • Climate Change - In a warmer world the atomsphere will have more energy leading to more intense storms and hurricanes. Some parts of the world will become wetter with an increased risk of flooding. Other parts of the world will become drier and prone to droughts and famine.
  • Farming - In low lying countries many people may live on flood plain and rivers depositing fertile silt put them at risk.
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Conservation Plates

  • The tectonic plates are sliding past each other.
  • The plates are moving in a similar direction at slightly different speeds and angles.
  • The sudden release of pressure causes an earthquake. At this type of margin plate, crust is neither destroyed or made.
  • As one plate moves faster than the other and in a slightly different direction, they tend to get stuck. Eventually, the build up of pressure causes them to be released.
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Destructive Subduction Plate Margins

  • The plates move together due to the convection currents in the mantle.
  • The denser oceanic crust sinks underneath the lighter continental crust in a process known as subduction. Great pressure is exerted and the oceanic crust is destroyed as it melts to form magma.
  • The magma rises because it is hotter and less dense resulting in volcanoes forming. This creates a deep ocean trench on the edge of the continental plate.
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Constructive Plate Margins

  • The tectonic plates are moving apart. This usually happens under the oceans.
  • As the plates pull away from each other, cracks and fractions form between the plates where there is no solid crust.
  • Magma forces its way into the cracks and makes its way to the surface to form volcanoes. In this way new land is formed as the plates gradually pull apart.
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Destructive Collision Plate Margins

  • The plates move together due to convection current in the mantle. The plates are the same - both continental crusts.
  • The plates are the same size and density so neither one will sink. Instead, they collide, when the two plates collide they buckle and force upwards to create fold mountains.
  • When two oceanic plates collide, the cooler, denser plate subducts. This forms a chain of volcanic islands called island arcs.
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Earthquakes - Primary Effect

  • Collapsed buildings
  • Roads destroyed
  • Lives lost
  • Schools, hospitals and other services destroyed
  • Bridges collapsed
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Earthquakes - Secondary Effects

  • Disease
  • Families destroyed
  • Tsunamis
  • Broken water & gas pipes
  • Homeless people
  • Poor sanitation
  • Fires
  • Landslides & avalanches
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Earthquakes - Immediate Responses

  • Field hospitals set up
  • Helicopters and rescue equipment
  • Social media pages up to help locate people
  • International appeals by NGOs
  • Tents for housing
  • Heavy lifting equipment provided
  • Satellite images used to map damaged areas
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Earthquakes - Long term Responses

  • Housing reconstruction
  • Stricter rules on building construction
  • Schools rebuilt
  • Roads repaired
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