Physical processes along plate margins

• what is meant by a natural hazard?

  a natural event that usually has negative impacts on society and the environment.
• types of natural hazard

  earthquakes + volcanoes (tectonic)

  flooding (geomorphological)

  tropical storms (Atmospheric)

  forest fires (Biological)
• Factors affecting hazard risk

  Climate change : warmer planet increases frequency + severity of tropical storms flooding and droughts.

  inequality: in poorer parts of the world, poverty may force ppl to live in areas at risks which makes them more vulnerable .

  Demographics: if areas are densely populated = greater risks from hazards

  type of hazards: some hazards are more devastating thsn others, some are more predictable.

  frequency + magnitude: weaker/less frequency hazards pose less threat compared to those that have a high magnitude or occur more often.
• plate tectonics theory


  earth is divided into the crust , mantle, outer core and inner core. area that includes the crust can be described as the asthenosphere and the upper section of the crust the lithosphere. the crust is like a jigsaw as it is seperated up into tectonic plates. it is due to the movement of these tectonic plates by convection currents that we get volcano eruptions and earthquakes.
• convection currents


  core is very hot due to radioactive decay. heat creates convection currents which travel into the mantle. they spread outwards as they begin to rise as their distance from the core inceeases. the convection currents sink as their temperature decreases. this completes the convection cell and causes the plates to move.
• slab pull

  slab pull occurs when there is subduction . the force is created as the plate sinks into the mantle + pulls the lower plate further away from the volcanic ridge where its formed.
• ridge push


  occurs when newly formed rock at the mid ocean ridge is warmer and less dense than the older denser rock below it. This makes the older rock slope down and push away from the ridge.
• Constructive plate margins

  Plates move away form each other due to the convection currents, magma rises upwards through the gap that had been created.

  this leads to the formation of volcanoes as the layers of lava build up establishing the volcano .
• destructive plate margins

  plates move toward each other , due to convection currents.

  when an oceanic plates meets a continental plate, the oceanic plate is forced under the continental as it is more dense.

  oceanic plate then melts to create magma, leading to the formation of volcanoes as magma can rise to the surface .
• conservative plate margins

  Plates move sideways past each other,rub against each other.

  Creating friction and pressure as the movement is not smooth

  stress eventually overcomes the frictional resistance, causing the sudden release of energy = generating the earthquake

  earthquake occurs at the focus but is felt at the epicentre
• no volacanoes are created here as there is no area created for the magma to come through.