Plate margins

• Lithosphere


  The solid outer surface of the Earth, made up of the crust and upper mantle - rock layer
• Crust


  • Solid out surface, thin. Continental crust
  • Oceanic crust
• Mantle


  • A solid layer that flows like a liquid but very slowly, upper portion is called the asthenosphere and can deform like plastic . Upper mantle
  • Lower mantle
• Plate tectonics


  1. Plates are a piece of the earth's crust. move very slowly over the upper mantle

  2. There are 3 types of plate margin: constructive, destructive and conservative
• Interactions between plates and mantle


  Cause earthquakes and volcanic activity
• Causes of plate movement

  • Ridge push- at mid ocean ridges new magma rises and cools. As it cools it becomes denser and slides down away from the ridge causing plates to move away from the ridge
  • Slab pull - as the plate sinks into the mantle because of gravity, it pulls the rest of the plate along with it.
  • Convection currents- hot rock rises from thr core towards the crust where it cool and sinks back down
• Constructive plate margin


  1. Oceanic plates are pulled apart

  2. Magma rises up and cools to form new oceanic crust

  3. Causes small earthquakes
• Volcanoes at constructive margins


  • Magma reaches the surface, forming low, wide shield volcanoes
  • Rift valleys form where land is being pulled apart
• Destructive plate margin


  1. Oceanic plate subducts under continental plate

  2. Friction, pressure and heat causes oceanic crust to melt

  3. Melted crust bubbles upwards to form explosive volcanoes
• Earthquakes at destructive margins


  Plates get stuck, pressure builds up until rock fractures along a fault line
• Conservative plate margins have earthquakes but no volcanoes
• Conservative plate boundary


  • Two plates move alongside each other, either in the same direction with one going faster, or in opposite directions
  • Friction causes the plates to become stuck, pressure builds up and the rock fractures in an earthquake
• Conservative plate boundary


  • San Andreas Fault, where the Pacific plate grinds alongside the North American plate
• Constructive plate margin


  Oceanic plates are pulled apart by slab pull and pushed apart by ridge push, magma rises up between the plates and cools down to form solid rock, forming new oceanic crust at the edge of the plate
• Formation of new oceanic crust at constructive plate margins


  1. Magma rises up between the plates

  2. Magma cools down to form solid rock

  3. New oceanic crust forms at the edge of the plate
• Constructive plate margins


  • New crust sometimes fractures as the plates move, causing small earthquakes
  • In most places, the magma never reaches the surface, but it does push up the crust, forming long ridges under the oceans
  • In a few places the rising magma has built large islands, and lava erupts on to the surface (e.g. Iceland)
• Shield volcanoes at constructive plate margins 


  Low, wide volcanoes formed because the lava is runny and spreads out before solidifying
• Rift valley at constructive plate margins


  Formed where tectonic forces first start to pull land apart, with steep sides and looking like tears in the land (e.g. East African Rift Valley)
• Destructive plate margin - Volcanoes


  An ocean plate and a continental plate move towards each other, the oceanic plate goes underneath the continental plate (subduction), the friction, pressure and heat from the mantle causes the oceanic crust to melt, the melted crust bubbles upwards because it contains gases and so is less dense, forming very explosive volcanoes (e.g. Chaiten in Chile)
• Destructive plate margin - Earthquakes


  As the oceanic plate dives underneath the overlying plate, it drags the overlying plate down with it, deforming it and forming fold mountains, the plates do not slide smoothly, friction causes plates to lock together, pressure builds up until the crust fractures usually along a fault line, the shockwaves are called seismic waves and the point on the surface where they reach first is called the epicentre, destructive margin earthquakes have the potential to be very large, sometimes the edge of the overlying plate flicks upwards, displacing sea water and causing a tsunami (e.g. Japan)