1.2.1 Tectonic Hazards

• The Earth is composed of 4 main layers:

  Inner core

  Outer core

  Mantle

  Crust
• Inner core:

  About 1400km in diameter, a solid and dense layer composed of iron and nickel with temperatures of about 5500 degrees Celsius
• Outer core:

  About 2100 km thick, a semi-molten metal layer with temperatures between about 5000 - 5500 degrees Celsius
• Mantle:

  About 2900km thick, a semi-molten layer which is less dense than the outer core
• Crust:

  The thickness varies, and is made up of two types of crust.
• There are two types of crust:

  The Oceanic crust and The continental crust
• The Oceanic Crust is thinner (5-10km) but heavier and denser
• The Continental crust is thicker (25-90km) but is older and lighter
• Oceanic crust is continually being created and destroyed as a result of plate movement, where it is denser and so subducts under the continental crust.

  This is why continental crust is much older than oceanic crust, as it isn't destroyed
• Plate tectonics

  • The crust is broken into a number of tectonic plates
  • These plates move on top of the semi-molten mantle below.
  • Tectonic theory once stated the movement of the plates was the result of convection currents in the mantle
  • Current theory is called slab pull theory which suggests that the movement is the result of the weight of the denser oceanic plates subducting and dragging the rest of the plate along
  • A plate boundary or margin is where two plates meet
• Volcano distribution

  • Most volcanoes occur at constructive and destructive plate boundaries
  • The majority of active volcanoes (approximately 75%) are located around the rim of the Pacific Ocean called the 'Ring of Fire'
  • Hotspots occur away from plate boundaries and are plumes/columns of magma which escape through the Earth's crust
• Distribution of Earthquakes & Volcanoes

  Earthquake distribution

  • Earthquakes occur at all types of plate boundaries
  • Most occur along the Pacific 'Ring of Fire' (approximately 90%)
• Plate Boundaries

  -Types of plate boundary

  • Volcanic eruptions and earthquakes most commonly occur at or near plate boundaries
  • There are three main types of plate boundaries:
  • Constructive
  • Destructive
  • Conservative (transform)
• Constructive plate boundary

  • At a constructive boundary the plates are moving apart
  • The Mid Atlantic Ridge is an example of a constructive plate boundary
  • Both volcanic eruptions and earthquakes can occur at this type of plate boundary
• Destructive plate boundary

  • At a destructive plate boundary the plates are moving together
  • The denser, heavier oceanic plate subducts under the lighter, less dense continental plate
  • The boundary between the Nazca plate and the South American plate is one example
  • Both volcanic eruptions and earthquakes occur at this type of plate boundary
• Conservative (transform) boundary

  • At a conservative (transform)boundary the plates move passed each other in opposite directions or in the same direction at different speeds
  • Earthquakes are the only hazard at this type of boundary
• The Primary Hazard of Tectonic Activity

  Volcanic Eruption

  • Ash
  • Pyroclastic flow (Clouds of superheated material up to 700 degrees centigrade which can travel up to 500 kmph)
  • Lava flow
  • Gas emissions
  • Volcanic bombs
• The Primary Hazard of Tectonic Activity

  Earthquake

  • Ground shaking
  • Gas emissions
• The Secondary Hazards of Tectonic Activity

  Volcanic Eruption

  • Lahars (When water(often from melting snow and ice) mixes with volcanic ash to create a fast moving mudflow)
  • Acidification (Sulphur emissions from volcanic eruptions increase the acidity of water)
  • Landslides
  • Climate change
  • Fires
  • Floods
• The Secondary Hazards of Tectonic Activity

  Earthquake

  • Building collapse
  • Landslides
  • Gas leaks
  • Fires 
  • Soil liquefaction (When loose material including soil and rock acts like a liquid due to an earthquake.)
  • Subsidence(The sudden sinking of the Earth's surface)
  • Mudflows
  • Tsunami