CGP Types of Plate Margin

• The next couple of pages build on some of the stuff you should have learnt at GCSE. It's not the most difficult of topics
• Earthquakes and Volcanoes Occur at Constructive Margins

  1. Contractive margin occurs where two plates are moving APART (diverging)

  2. Mantle is under pressure from the plates above

  3. When plates move apart, pressure is released at the margin

  4. Release of pressure causes the mantle to melt producing magma

  5. Magma is less dense than the plate above, so it rises and can erupt to form a VOLCANO

  6. Plates don't move apart in a uniform way, some parts move faster than others

  7. Pressure builds up

  8. When pressure becomes too much, the plate cracks, making a fault line and causing an EARTHQUAKE

  9. Further earthquakes may also occur along the fault line once it's been created
• Constructive margins


  • Create two different landforms, depending on where they are
• Ocean Ridge


  • Where diverging plates are underwater, an ocean ridge forms
  • Underwater volcanoes erupt along mid-ocean ridges and they can build up to be above water level, e.g. Iceland
• Rift Valley


  • Where plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines
  • As the plate keeps moving apart, the crust between parallel faults drops down to form a rift valley, e.g. the East African Rift System
  • Volcanoes are found around rift valleys, e.g. Mount Kilimanjaro and Mount Kenya
• Earthquakes and Volcanoes Also Occur at Destructive Margins

  1. Destructive margin occurs where two plates are moving TOWARDS EACH OTHER (converging)

  2. Where continental crust and oceanic crust converge, the more dense oceanic crust is forced under the less dense continental crust (it's subducted), forming a DEEP SEA TRENCH

  3. FOLD MOUNTAINS also form where the plates meet, made up of sediments that have accumulated on the continental crust, which are folded upwards along with the edge of the continental crust

  4. The oceanic crust is heated by friction and contact with the upper mantle, which melts it into magma

  5. The magma is less dense than the continental crust above and will rise back to the surface to form VOLCANOES

  6. As one plate moves under the other they can get stuck, causing pressure to build up

  7. When the pressure becomes too much, the plates jerk past each other causing an EARTHQUAKE

  8. Most of the same processes occur where two plates of oceanic crust are moving towards each other - the denser of the two will be subducted, forming a DEEP SEA TRENCH and triggering EARTHQUAKES and VOLCANIC ERUPTIONS

  9. Volcanic eruptions that take place underwater (e.g. when two plates of oceanic crust converge) create LAND ARCS - clusters of islands that sit in a curved line, e.g. the Mariana Islands
• Only Earthquakes Occur at Conservative Plate Margins


  • Conservative margin occurs where two plates are moving PAST EACH OTHER
  • The two plates get locked together in places and pressure builds up
  • As with destructive margins, this can cause the plates to jerk past each other, creating fault lines, releasing the energy as an EARTHQUAKE
  • For example, the Pacific plate is moving past the North American plate, causing many earthquakes along this margin and along fault lines, e.g. the San Andreas fault in California
• Magma Plumes Can Form Volcanoes Away From Plate Margins

  1. A magma plume is a vertical column of extra-hot magma that rises up from the mantle

  2. Volcanoes form above magma plumes

  3. The magma plume remains stationary over time, but the crust moves above it

  4. Volcanic activity in the part of the crust that was above the magma plume decreases as it moves away

  5. New volcanoes form in the part of the crust that is now above the magma plume

  6. As the crust continues to move, a chain of volcanoes is formed

  7. The chain of islands that makes up Hawaii was formed by a magma plume
• The ground above a magma plume is called a hotspot
• Tectonic plates are great - but they do have their faults...