Tectonic hazards

• Geological (Tectonic) Hazards =

  Tectonic hazards are caused by the movement of tectonic plates.

  These include:

  • Earthquakes  
  • Volcanoes 
  • Tsunamis 
• The earth has 4 layers:

  • The crust
  • The mantle
  • The inner core
  • The outer core
• The Crust

  The crust is the thinnest layer of the Earth. It is broken into several pieces know as tectonic plates. These plates move around on the mantle. There are 2 types of plate: oceanic and continental.

  Continental crust forms the land and is made mostly of granite, it isn’t very dense (heavy) and averages between 30-50 km. 

  Oceanic crust is much thinner, but heavier than the continental crust (more dense). It’s around 6-8 km thick and is made of a rock called basalt.
• The Mantle

  • The mantle is that portion of our planet that lies between the Earth’s crust and core.  
  • The mantle makes up 84% of the Earth
  • It is the thickest layer of the Earth.
• The mantle's outer layer consists of molten or liquid rock known as magma. The Earth’s tectonic plates float on top of the mantle. 
• The Core

  
  

  Outer core

  • It is a liquid between 4000-5000°C.

  Inner core

  • Solid metal made of Nickel and Iron
  • This part gives the Earth its magnetic field. 
  • It’s the hottest part of the Earth and is over 5000°C. 
• Magma

  Magma is the melted rock beneath the earth's surface. However, when it does reach the surface it is now called lava.
• Tectonic plates

  These float on top of the magma and interact with one another.
• Plate Boundary

  This is where tectonic plates meet - This is where tectonic hazards occur most frequently and severely.
• Continental drift =

  The gradual movement of the continents across the earth's surface through geological time.
• Plate Tectonic Theory

  250 million years ago the world looked like this, all the continents were joined together to form a supercontinent – Pangaea. Identical rocks and fossils dating from this time have been found in West Africa and South America, this tells us that they were once joined together.
• What makes the surface of our crust move?

  Convection currents, that occur within the molten rock in the mantle move the Tectonic plates in different directions. 

  The direction of movement and type of plate margin is determined by which way the convection currents are flowing.
• Convection currents


  1. The Earth’s core heats up the rock in the lower mantle

  2. The rock in the lower mantle melts (turns into liquid) and expands as it gets heated

  3. Heated, molten (liquid) rock is less dense (lighter) than the surrounding rock and then rise away from the core

  4. As the molten rock rises, it reaches the crust and it spreads sideways

  5. The thick, molten rock sticks to the bottom of the tectonic plate and drags it along with it

  6. As the molten rock is further away from the heat of the core, it starts to cool and become denser (heavier)

  7. As it becomes cooler and heavier it sinks back down towards the core, ready to be heated again
• DIFFERENT NAMES FOR PLATE BOUNDARIES

  1. Constructive
  2. Destructive 
  3. Conservative 
• Constructive or divergent plate boundary

  = the plates move apart.
• Destructive or convergent plate boundary

  = plates move towards each other
• Conservative plate boundary

  = plates slide past each other.
• Destructive or convergent plate boundary

  Two plates that move towards one another are the oceanic plate and continental plate. 

  The oceanic plate is heavier / denser so it goes beneath the continental plate into the mantle and is destroyed. 

  The areas where the plates meet is the subduction zone where the oceanic plate is subducted 

  Friction and pressure builds up causing an earthquake 
• Constructive or divergent plate boundary

  When the two tectonic plates move apart magma rises from the mantle to fill the gap (volcano) and when it cools it forms new crust
• Conservative plate boundary

  Only earthquakes occur at a conservative plate margin. 

  Two plates moving alongside each other, either in different directions or in the same direction but at different speeds. 

  Tension builds up when the plates grind past each other and get stuck creating an earthquake. 
• Primary effects of tectonic hazards

  • Buildings and roads are destroyed by the shaking of the ground during an earthquake
  • People are injured and killed when buildings collapse
• Secondary effects of tectonic hazards:

  • Food shortages can occur if crops are damaged, livestock is killed or supply lines are damaged
  • Earthquakes can trigger tsunamis, which cause enormous waves and coastal flooding.
  • Gas pipes and electricity cables are damaged, cutting off supplies
  • Aid and emergency vehicles cannot access areas which need help, this can cause more deaths
• Primary effect = the immediate impacts caused by the hazard itself

  Secondary effect = the indirect impacts of an event, which occurs after. For example, after hours, weeks, months or even years after the event. They can be other hazards caused by the main hazard, for example, tsunamis and landslides are secondary effects of an earthquake.
• Immediate response = are those which take place in the days and weeks after the disaster
• Long - term Response = are those which go on for months or years after a disaster.
• Immediate responses:

  • Evacuating people
  • Provide food, shelter and water
  • Charities may send aid workers with supplies
• Long - term responses:

  • Repairing homes and rehousing those whose homes have been destroyed
  • Improve building regulations so buildings can withstand future hazards.