Plate margins


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AQA A2 tectonics powerpoint on the types of plate margin

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Plate margins

  1. 1. Types of plate margin <ul><li>There are 2 types of crust: </li></ul><ul><li>Continental crust which is older, thicker and less dense than… </li></ul><ul><li>Oceanic crust which is younger, thinner and denser </li></ul><ul><li>There are 3 directions of movement between plates: </li></ul><ul><li>Converging: where 2 plates are moving towards each other </li></ul><ul><li>Diverging: where 2 plates are moving away from each other </li></ul><ul><li>Passive: where 2 plates are moving side by side </li></ul><ul><li>There are 6 different combinations of types of crust and directions of movement: </li></ul><ul><li>Destructive – where oceanic and continental crust converge </li></ul><ul><li>Destructive – where oceanic and oceanic crust converge </li></ul><ul><li>Destructive (Collision) – where continental and continental crust converge </li></ul><ul><li>Constructive – where 2 plates diverge under the ocean </li></ul><ul><li>Constructive – where continental crust is diverging </li></ul><ul><li>Conservative – where 2 plates move parallel to each other </li></ul><ul><li>Each of the 6 combinations above create different tectonic hazards and produce different landforms. </li></ul>
  2. 2. <ul><li>Description </li></ul><ul><li>denser oceanic crust is subducted </li></ul><ul><li>friction and heat cause partial melting of the crust </li></ul><ul><li>this magma is less dense than the mantle and rises / forces its way through fissures in the lithosphere </li></ul><ul><li>Landforms </li></ul><ul><li>deep ocean trenches such as the Peru-Chile trench </li></ul><ul><li>Fold mountains from rock scraped off the descending plate and folding of the continental crust </li></ul><ul><li>Hazards </li></ul><ul><li>Violent volcanoes (composite cone) – due to viscous acidic lavas which block the vents in the volcanoes </li></ul><ul><li>Powerful earthquakes </li></ul>1. Destructive boundary - Continental / oceanic convergence
  3. 3. <ul><li>Description </li></ul><ul><li>2 plates with oceanic crust collide </li></ul><ul><li>the densest crust will be subducted </li></ul><ul><li>Landforms </li></ul><ul><li>Deep ocean trenches e.g. the Marianas trench </li></ul><ul><li>Island arcs as volcanoes rise out of the sea e.g. Caribbean, Philippines, Japan, Indonesia </li></ul><ul><li>Hazards </li></ul><ul><li>Violent earthquakes and volcanoes </li></ul>2. Destructive boundary - Oceanic / oceanic convergence
  4. 4. <ul><li>Description </li></ul><ul><li>Subduction of oceanic crust brings 2 continental masses together </li></ul><ul><li>Both have a similar density so can’t be subducted </li></ul><ul><li>Sedimentary rocks scraped off the old sea floor are compressed together to form young fold mountains </li></ul><ul><li>Landforms </li></ul><ul><li>Young fold mountains such as the Himalayas (created in the last 40 million years) These are still growing despite erosion </li></ul><ul><li>Hazards </li></ul><ul><li>Earthquakes as powerful as at destructive margins </li></ul>3. Collision boundary - Continental / continental convergence
  5. 5. <ul><li>Description </li></ul><ul><li>plates are moving away from each other causing the crust to weaken and hot magma to force upwards creating a ridge </li></ul><ul><li>in the centre of the ridge, the crust can subside into to magma below creating a valley </li></ul><ul><li>the fissures (splits) in the crust provide a route for the more fluid lavas to escape if these continue submarine volcanoes form </li></ul><ul><li>Landforms </li></ul><ul><li>Mid-ocean ridges </li></ul><ul><li>Volcanic islands e.g. Iceland, Surtsey </li></ul><ul><li>Hazards </li></ul><ul><li>Volcanoes that erupt with basic (runny) lava – more frequent & less violent eruptions </li></ul><ul><li>Shallow focus earthquakes </li></ul>4. Constructive boundary – sub-marine divergence
  6. 6. <ul><li>Description </li></ul><ul><li>occurs where spreading occurs beneath the continents </li></ul><ul><li>the up-welling magma leads to fracturing and rifting </li></ul><ul><li>central sections collapse to form rift valleys </li></ul><ul><li>volcanoes form where magma forces its way through fissures </li></ul><ul><li>Landforms </li></ul><ul><li>Rift valleys such as East African Rift valley – these can widen and eventually get flooded by the sea e.g the Red Sea </li></ul><ul><li>Volcanoes such as Mt Kilimanjaro & Mt Kenya </li></ul><ul><li>Hazards </li></ul><ul><li>Volcanoes </li></ul><ul><li>Shallow focus earthquakes </li></ul>4. Rifting – continental divergence
  7. 7. <ul><li>Description </li></ul><ul><li>plates are moving parallel to each other, no collision or subduction occurs </li></ul><ul><li>movement is erratic as plates stick together, pressure builds up and is released in a sudden movement </li></ul><ul><li>Landforms </li></ul><ul><li>Fault lines such as the San Andreas and Hayward faults </li></ul><ul><li>Hazards </li></ul><ul><li>No volcanoes </li></ul><ul><li>Earthquakes as powerful as at destructive margins </li></ul>4. Conservative boundary – passive movement