How do plate tectonic shape our world?

• Structure of the Earth

  • inner core, 1400km in diameter, solid and dense layer composed of iron and nickel with temperatures of 5500 degrees Celsius.
  • outer core, 2100km thick, semi-molten layer with temperatures between 5000-5500 degrees Celsius.
  • mantle, 2900km thick, semi-molten layer which is less dense than the outer core.
  • crust, made up of two types of crust, continental and oceanic.

  
• Crust

  • oceanic crust, thinner, 5-10km but is heavier and denser.
  • continental crust, thicker, 25-90km but is older and lighter.
  • oceanic crust is denser so subducts under the continental crust.
• Plate tectonics

  • the crust is broken into a number of tectonic plates.
  • tectonic plates move on top of the semi-molten mantle below.

  
• Ridge push and slab push

  • the movement of the plates was the result of convection currents in the mantle.
  • ridge push, the new crust forming at the constructive boundary which then pushes the older crust away.
  • slab pull, the weight of the denser oceanic plates subducting and dragging the rest of the plate along.
  • a plate boundary or margin is where the two plates meet.

  
• Earthquake distribution

  • earthquakes occur at all types of plate boundaries, most occur along the Pacific Ring of Fire.

  
• Volcano distribution

  • most volcanoes occur at constructive and destructive plate boundaries.
  • the majority of active volcanoes are located around the Ring of Fire.
  • hotspots occur away from plate boundaries and are plumes of magma which escape through the Earth's crust.

  
• Constructive plate boundary

  • the plates are moving apart.
  • the Mid-Atlantic Ridge is an example.
  • both volcanic eruptions and earthquakes can occur at this type of plate boundary.

  
• 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 an example.
  • both volcanic eruptions and earthquakes occur at this type of plate boundary.

  
• Collision boundary

  • two continental plates are moving towards each other.
  • they are less dense than the mantle below them so they do not subduct.
  • the crust is forced upwards forming fold mountains such as the Himalayas.
  • At a collision boundary there are no volcanoes but earthquakes do occur.

  
• Conservative boundary

  • the plates move past each other in opposite directions or in the same direction at different speeds.
  • earthquakes are the only hazard at this type of boundary.

  
• Earthquakes and plate boundaries

  • they can occur anywhere but mostly at or near any type of plate boundaries.
  • earthquakes are the result of pressure building when tectonic plates move.
  • the epicentre is the point on the Earth's surface directly above the focus.
  • the focus is the point at which the earthquake stars below the Earth's surface.
• Measuring earthquakes

  • seismometers are used to record the size of the seismic wave.
  • the magnitude by earthquakes is measured on the moment magnitude scale which replaced the Richter scale.
  • the damage caused by earthquakes is measured on the Mercalli scale.

  
• Earthquake focus

  • the depth of the earthquake focus can affect the impact of an earthquake.
  • a deep focus earthquake starts at a depth greater than 70km below the surface, they tend to occur at destructive plate boundaries and may be very powerful, the seismic waves tend to move vertically so a smaller area is affected.
  • a shallow focus earthquake starts at a depth less than 70km below the surface, they can occur at all plate boundaries and tend to be less powerful, the seismic waves tend to move horizontally so a larger area is affected.
• Earthquake sequence

  • as the tectonic plates move, they can get stuck.
  • pressure builds as the plates continue to try to move.
  • eventually the plates jolt free and the pressure is released as energy.
  • the point at which the earthquake starts is the focus.
  • the epicentre is the point directly above the focus on the earth's surface.
  • the energy passes through the Earth's crust as waves which is the earthquake.
  • they can happed as a result of human activity such as drilling into crust or mining.

  
• Structure of volcanoes

  • a volcano is formed when magma erupts onto the Earth's surface as lava through a vent in the Earth's crust.
  • the magnitude of a volcanic eruption is measured on the Volcanic Explosivity Index.
  • due to the type of lava erupted the formation of volcano varies.

  
• Composite volcano

  • steep sided.
  • viscous lava.
  • more explosive eruptions.
  • formed from alternating layers of ash and lava.
  • tend to form on destructive plate boundaries.

  
• Shield volcano

  • gently sloping sides.
  • runny lava.
  • less explosive and gentle eruptions.
  • tend to form on constructive plate boundaries or hot spots.
  • frequent eruptions.

  
• Volcanoes at a hotspot

  • at a hot spot the tectonic plate passes over a plume of magma.
  • the magma rises to the surface through cracks in the crust.
  • as the tectonic plate moves slowly over the magma plume a line of island may form, such as Hawaii.

  
• Case study Nepal earthquake

  • Nepal is one of the poorest countries in the world with a GDP under $1000.
  • located between China and India, Nepal is a land locked country.
  • in April 2015 Nepal was struck by an earthquake with a magnitude of 7.8.
  • the epicentre was 80km northwest of Kathmandu in the Gorka district.
  • the focus was shallow at only 15km beneath the surface.
  • over 3000 aftershocks followed the main earthquake.

  
• Cause of the earthquake

  • Nepal is located on a collision boundary between the Indian and Eurasian plates.
• Effects of the earthquake

  • 9000 deaths and 20,000 injured.
  • electricity and water supplies cut.
  • 7000 schools and 1000 health facilities were damaged or destroyed.
  • 4.5 million people were made homeless.
  • offices, shops and factories were destroyed meaning people were unable to make a living.
  • UNESCO world heritage sites were destroyed.
  • landslides which blocked roads and rivers.
  • damages estimated between $7-10 billion which is about 35% of the GDP.
• Immediate responses to the earthquake

  • donations of money and aid from around the world totalling $3 billion, $51 million from the UK.
  • aid in the form of temporary shelters, medicines, food and water, clothing, search and rescue teams, medical staff.
  • 90% of the Nepalese army were mobilised.
  • tent cities were set up in Kathmandu for those made homeless.
  • GIS crisis mapping tool was used to co-ordinate the response.
  • $3 million grant provided by the Asian Development Bank for emergency relief.
• Long term responses to the earthquake

  • landslides were cleared and roads repaired to restore access to remote rural communities.
  • schools were rebuilt.
  • earthquake drills were introduced to provide people with education about what to do in the event of an earthquake.
  • stricter building cores with more enforcement.
  • $200 million was provided by the Asian Development Bank for rebuilding.
  • a new government task force was set up to plan for future earthquake events.
• Prediction of earthquakes

  • accurate predictions are not currently possible but monitoring is.
  • many different methods of monitoring are being used to help research possible prediction methods such as tiltmeters which monitor ground changes, clusters of small earthquakes, changes in radon gas emissions, changes in animal behaviour and remote sensing of ground movement using satellites.
• Building design preparation

  • in developed countries building design and engineering is commonly used to reduce the impact of earthquakes.
  • shutters of windows prevent falling glass.
  • cross-bracing of steel frames.
  • foundations sunk deep into the bedrock.
  • frames which sway with the earthquake tremors.
  • rubber shock absorbers to reduce tremors moving through buildings.
• Land planning preparation

  • mapping of areas most at risk from earthquakes.
  • planning can ensure valuable services like the fire service and hospitals are not built in high risk areas.
  • densely populated housing can be located away from high risk areas.
• Drills and education preparation

  • earthquake drills help people to prepare for what to do in an earthquake to protect themselves.
  • education about how to prepare homes means that people are less likely to be injured by falling objects and furniture.
• Remote sensing and GIS

  • remote sensing of the Earth's surface by satellites provides data about changes in ground movement.
  • GIS provides layers of data such as vulnerable areas, land use, infrastructure such as roads.
  • GIS data is then used to assist with land use planning.
• Nepal reparations before the earthquake and issues with preparation

  • 1997 the Nepali government created KVERMP which included SESP providing funding to schools for earthquake drills, training to make buildings resistant to earthquakes. however, was mainly in urban areas, people in rural areas did not have drills.
  • Improved 1994 National Building Code and training building inspectors. however, the code was ignored and buildings were still not earthquake resistant.
  • Nepal Red Cross Society had 12 warehouses stocked of emergency supplies. however they weren't enough for the scale of the disaster.