Plate Tectonic Revision

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  • Created on: 15-06-14 17:56
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Structure of the Earth
Inner Core Outer core Mantle Crust
Solid, iron and nickel. Semi-molten, Semi-solid. Asthenosphere Divided into plates. Asthenosphere + lithosphere
5000°. Lots of (upper mantle) - 20km thick. = 80km thick. Oceanic crust SIMA (young
iron and Magnesium and iron and <200myo) mainly granite, 6-10km thick + denser
nickel. silicate rocks. than Continental crust (>1500myo) SILA (old)
65km thick and less dense, mainly basalt.
Plates ­ there are 7 large pieces of the lithosphere they float on asthenosphere and move through convection currents.
Mohorovicic discontinuity ­ boundary between Earth's crust and the mantle
Conrad discontinuity - boundary within the Earth's crust
Francis Bacon 1620 Continental fit ­ puzzle-like fit
1965 Tuzo Wilson ­ Hotspots
Alfred Wegener, German 1915
Coastlines of South America and Africa ­ suggested continents were joined together
Originally one continent, Pangaea
Split into super continents (Laurasia and Gondwanaland) he couldn't prove it so theory was dismissed
Harry Hess Sea floor spreading in Mid-Atlantic Ridge brought his theory back to light ­ he noticed that the plate grew from
the ocean ridge ­ oldest material was along the coasts.
Glacial deposits of similar ages in Brazil and West Africa
Geologically corresponding mountains in US (Appalachian) and NW Europe (incl. Scotland)
Coal deposits in tropical regions ­ decay of plants ­ coal deposits found in UK.
Fossil remains of the Mesosaurus (270 million years extinct) found in South Africa and Brazil. Mesosaurus is a freshwater
reptile ­ remains found in areas that would have meant crossing saltwater oceans.
Fossilised plants e.g. Glossopteris, a tree like plant found in Africa, Antarctica, Australia and South America.
Frederick Vine and Drummond Matthews looked at patterns of magnetic stripes (symmetrical) on ocean floor.
Polar Wandering Curve - plotting the polar positions of iron in rocks aligns with the poles of different ages ­ shows how the
land moved.
Paleomagnetism shows periodically reversing magnetic fields (shown by sea floor spreading) once every 200,000 years or
so, the Earth's magnetic field reverses polarity (the poles switch)
As magma erupts from mid-ocean ridges, magnetic minerals in the molten rock align themselves with the direction of the
earth's magnetic field. When the crust is solidified, the alignment is fixed, iron particles. Alternating stripes where new floor
is created and the poles switch.
Radioactive decay of some elements in the mantle and core, e.g. uranium, generates lots of heat. When lower parts of the
asthenosphere heat up they become less dense, and slowly rise. As they move towards the top of the asthenosphere they cool
down and become denser and slowly sink. These circular movements of semi-molten rock are called convection currents. They
drag the base of the tectonic plates which causes them to move. Basalt material fills the gap.
N. American + Eurasian = Mid-Atlantic ridge
African = Somali + Nubian = East African Rift Valley
Mount Nyiragongo, Congo 2002
At constructive boundaries volcanoes basic volcanoes and destructive they are explosive acidic volcanoes
CONVERGENT/DESRTRUCTIVE (continental + oceanic sinks = subduction) (oceanic + oceanic subduction) OR COLLISION
(two continental = fold mountains)
Destructive e.g. Nazca + S. American plates Collision e.g. Indian and Eurasian plate (Mountains e.g.
Himalayas). (Sichuan earthquake 2008).
Peru-Chile trench as oceanic crust is subducted
Earthquakes due to the heat created as the Nazca plate is
destroyed. Tohuku earthquake and tsunami March 2011.
Torre Mayor, Mexico City + Sky Tower, New Zealand.
Fold mountains e.g. Andes

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Volcanoes e.g. Nevada Del Ruiz 1985. Montserrat Soufriere
Hills 1995-1998. Mount Etna, Sicily 1983. Mount Krakatoa,
Indonesia 1883. Pinatubo, Philippines 1991. Mount St.
Helens, Washington DC 1980. Solfatara, Naples, Italy 1198.
CONSERVATIVE (side by side/same direction different speeds)
No earthquakes - shallow focus earthquakes
Pacific (fastest 5-9cm/year) vs N. American plates = San Andreas Fault, California
E.g. Hawaiian Islands, hotspot within pacific plate. Radioactive elements within the mantle, magma rises to surface in plumes,
forming shield volcanoes.…read more

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Pahoehoe flow: Is fluid rather than viscous, but does not move quickly. Often the surface layer is static whilst flow
continues beneath.
Shield ­ often occur at constructive margins, basaltic
lava, short and wide e.g. Mauna Loa, Hawaii
Fissure ­ elongated crack of surface crust, basaltic
lava (runny) rises up e.g. Mid-Atlantic Ridge
Acidic Dome ­ often at destructive margins, viscous
lava, tall and steep e.g.…read more

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Swelling ground (rising magma)
Seismic activity (splitting rock), smaller tremors
Groundwater levels
Emission of gases ­ high sulphur content = volcano close to erupting e.g. Lake Nyos 1986 limnic eruption
Changes in the magnetic fields
Animal behaviour
Training and education ­ in Japan one day a year is dedicated to "acting out" what to do in the event of an earthquake. USA,
New Zealand raised awareness in brochures.…read more

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Love waves can only travel through solids. They move the surface from side to side. These waves cause the most damage
due to their shearing effect; they are also the slowest waves.
Rayleigh waves can travel through liquids and solids. They radiate from the epicentre in a rolling motion.
Benioff zone the point at which two plates subduct and melt. Earthquakes originate from this point.…read more


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