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Plate techtonics



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  • 1. Plate tectonics
  • 2. Plates
    • 2 plates meet and push together
    • The continental plate folds upwards
    • The oceanic plate sub ducts, this forms a deep ocean trench.
    • The 2 plates keep moving towards each other and this causes friction.
    • Friction causes heat which melts the plates
    • The magma created, forces its way out, causing the volcano to erupt
    • The force of the 2 plates rubbing against each other causes earthquakes.
    • Sea floor sediments are scrapped off and folded into mountain
  • 3. Evidence of Plate tectonics
    • Jigsaw like fit of continents
    • Fossils found only in certain parts of the world that are separated by sea, also with certain rock types and formations.
    • Glacial deposits is more tropical conditions
    • Coal deposits in colder countries (UK)
    • Long line of volcanoes down the mid-Atlantic ridge, suggesting movement of plates.
  • 4. Structure of Earth
    • Solid Inner core- pressures so great its unable to melt even at extremely high temperatures.
    • Liquid outer core – pressure slightly lower so is molten
    • Mantle – thickest layer, dense and mainly solid
    • Asthenosphere – Upper portion of mantle, molten, this allows plates to move
    • Lithosphere – the solid rocks of earths surface
    • Crust – tectonic plates.
  • 5. How the plates move
      • Core is extremely hot
      • Upper mantle relatively cool
      • Hot material from mantle rises to surface
      • As material gets to top, it cools and sinks again.
      • This causes convection currents.
      • Some think the diverging currents cause the crust to split and diverge
      • Others believe that the sinking material drags the plate under, could be a combination
  • 6. Location of plate margins
    • Location of volcanoes and earthquakes
    • Ocean trenches
    • Gravity anomalies
    • Active faults
  • 7. Fissure eruptions
    • Occur where fissure in the earths crust dominate volcanic activity
    • Currents from the mantle slowly push the 2 crusts apart, certain area’s split into a series of fissures
    • Fissures will then begin to erupt with 100m high of lava.
    • After several weeks eruptions stop, lava cools and seals up the fissures
    • A row of small cinder cones can be seen
  • 8. Conservative boundaries + Hot Spots
    • Conservative boundaries are formed when Plates move alongside each other and crust is neither created or destroyed
    • Evidence of this – a fault or contrasting geology either side of fault
    • Hotspots are a point in the middle of a plate where eruptions occur
  • 9. Sea Floor Spreading
    • Rising magma in mantle causes a bulge in the crust
    • The crust will eventually break due to the rising magma’s pressure
    • Magma will escape through faults in boundary
    • Magma cools quickly (as it is underwater)
  • 10. Case study – Mt St Helens May 18 th 1980
    • Buildings buried
    • More than 200 houses destroyed
    • More than 185 miles of highway destroyed or damaged
    • Wildlife suffered – no home and death, salmon
    • Forrest damage – timber
    • Caused avalanche, mudflows and flooding
    • Crusting of ash helped grow crops in summer
    • Ash fall caused transportation problems – highways and roads closed, Airports shut due to lack of visibility
    • Ash caused pollution And damage to electrical systems many blackouts experienced
    • Unemployment rose in Mt St Helens region
    • Tourism down
  • 11. Earthquakes
    • 3 types are: constructive (extensional), destructive (compressional) and conservative (transform)
    • Compressional cause the most damage
    • Quakes tend to occur in clusters, that strike the same area within a limited time period
    • Largest quake in the cluster is called the mainshock, those before are called foreshock and those after the aftershock
    • Undersea tremors can cause tidal waves (seismic sea waves or tsunami)