Plate Tectonics

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  • Created by: EmmBlr
  • Created on: 01-06-17 15:43
What is a natural phenomenon?
Rare, remembered for a long time, caused by the natural environmnet, DOESN'T affect anyone.
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What is a hazardous event?
Something that has potential to be dangerous, caused by th natural environment, threatens life and property.
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What is a natural disaster?
Something caused by the natural environment that has potential to cause death and destruction, DOES affect life and people - at least fatalities or $16 billion of damage.
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What is Risk Perception?
People may accept the hazard - fatalistic. They may dominate the hazard - science can predict their occurence. Or they may adapt to the hazard.
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Describe the Inner core.
The centre, the hottest part of the Earth. It is solid and cosists of iron and nickel. Temperatures up to 5500. Provides immense heat energy.
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Descibe the outer core.
Layer surrounding the inner core. It is liquid, and also made of iron and nickel. Extremely hot, temperatures similar to the inner core.
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Describe the mantle.
About 2900km thick and made of semi-molten rock, magma. Rock in the upper mantle is hard, lower down the rock is soft and beginning to melt (asnethospere). Convection currents in the mantle drive the movement of the plates.
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Describe the Crust
Thin, between 0-10km thick. Solid rock outer layer. There are two types of crust. Oceanic Crust - basaltic in nature (known as sima - or silica and magnesium). Continental crust - composed of igneous, metamorphic and sedimentary rock. Less dense.
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What do the upper mantle and crust form?
Lithosphere
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What happens in the Lithosphere?
Plate tectonics are formed and destroyed.
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What shape is the Earth?
A geoid. It bulges at the equator and is flatter at the poles. This is due to centrifugal forces.
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How are the magnetic fields created?
The rotating Earth causes the liquid in the outer core to spin, creating a magnetic field.
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What causes the convection currents?
Hot spots around the core heat the asnethospere, creating a rising thermal current before spreading in the lithosphere, cooling and sinking again.
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What was Alfred Wegener's Theory?
Theory of continental fit. He suggested all the present continents were joined to form a supercontinent - Pangea.
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What evidence did Wegener have?
The jigsaw fit of South America and Africa. Matching rock sequences linking NW Scotland and East Canada. Coal (formed in tropical conditions) found in Antarctica. Glacial deposits and striations in Brazil match ones found in West Africa.
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What problem did Alfred Wegener have?
His theories did not explain how continental drift works.
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How was the continental shelf off the Atlantic coast discovered?
Seismic waves from dynamite used to reveal structures in the ocean. Discovered in 1935. Further exploration showed it was made of thin, young sedimentary oceanic crust of volcanic basalt.
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What significance did Marie Tharp and Bruce Heezen have?
First to scientifically map the topography of the ocean floor. their maps revealed the underwater ridge. 1953, Tharp observed depressions in the ridge that appeared to be a continuous crack - now called deep ocean trenches
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Whart is Seafloor spreading?
It was discovered that oceans were shallower in the middle. Hess suggested molten basalt oozed from the mantle at the ridges, creating a new seafloor which spread out in both directions. Older floor cooled and subsided to the abyssal plain.
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What did Vine and Matthews discover?
Patterns of magnetic stripes on the ocean floor. The symmetrical pattern suggested the Earth's magnetic field flipped over time. When it cooled, small magnetite crystals in the rock record the polarity of the Earth's field.
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What is Palaeomagnetism?
Studying the magnetism in rocks. Studies effectively confirm seafloor spreading and continental drift. Every 400,000 years or so the Earth's magnetic field switches polarity. The oldest lavas were furthest away from the ridge.
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What happens at a contructive plate margin?
Plates diverge - move away from one another.
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Geographical features of constructive plate margins
New oceanic crust, from rising basaltic lava. New Basaltic rocks. Mid-ocean ridges, broken up by transform faults. Shallow-focus earthquakes. Submarine, basic volcanoes. Volcanic islands. Continental Rift Valleys.
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What happens at destructive plate margins?
Plates converge - move towards each other.
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Geographical features at destructive plate margins: oceanic v. oceanic
Subduction zone. Deep ocean trenches. Island arcs. Shallow, intermediate and deep-focus earthquakes. Explosive, acid volcanoes.
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Geographical features at destructive plate margins: oceanic v. continental
Subduction Zone. Deep ocean trenches (Peru-Chile trench). Continental landmass uplifted and buckled into fold mountains. Intermediate and deep-focus earthquakes. Explosive, acid volcanoes.
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Geographical features at destructive plate margins: Continental v. continental
Fold mountains from colliding plates. Shallow-focus earthquakes.
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What happens at Conservative plate margins?
Plates move past or parallel to each other.
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Geographical Features at Conservative plate margins
Shallow-focus earthquakes
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Exceptions to plate margins
Hot spots (Basic volcanoes), Intraplate earthquakes.
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What is an Intraplate earthquake?
Occurs on the interior of a tectonic plate. Not sure of the causes. Can be very dangerous as they are in areas unaccustomed to earthquakes and buildings not usually seismically retrofitted.
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Describe Mid-Ocean ridges
Oceanic divergence. Plates pull apart and rift, magma rises, cools and is pulled away. Submarine volcanoes form here. Eg.g Mid-Atlantic Ridge.
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Describe Transform Faults
Oceanic divergence. Cut across ocean ridges at 90 degrees to the plate boundary, separating sections of the ridge. Can create frictional stress and tension, allowing shallow-focus earthquakes.
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Describe Fold Mountains
Oceanic and Continental and Continental and Continental convergence. The continental mass, and sediments between, is uplifted, compressed, buckled and folded into to chains of mountains e.g. Andes
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Describe Rift Valleys
Continental Divergence. The lithosphere stretches, causing it to fracture into sets of parallel faults. Land between collapses into deep, wide valleys separated by upright blocks of land called horsts. E.g. the Great African Rift Valley.
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Describe the Formation of New Basaltic rocks
Oceanic divergence and hot spots. Dried cooled lava from erupted volcanoes/magma spilled from Mid-Ocean ridges. Same basaltic rock in Scotland and Greenland as they moved apart.
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Describe Grabens
Continental divergence. As rift valleys pull apart the land between drops down further than before due to a release in pressure. E.g. the Great African Rift Valley
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Describe Island Arcs
Oceanic convergence and divergence. One plate subducts beneath the other creating a deep ocean trench. Magma rises from the Benioff zone creating a submarine volcano. The volcano develops over time and a chain of them form an island arc. Marianas arc
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Describe Submarine Volcanoes
Oceanic divergence or convergence. Volcanic eruptions along mid-ocean ridges or deep ocean trenches. Can grow into volcanic islands e.g. Surtsey
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Describe Shield (Basic) Volcanoes
Mid-Ocean ridges, rift valleys and hot spots. Repeated eruptions of runny lava from a central vent form gently sloping volcanic cones and shields. e.g. Hawaiian volcanoes
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Describe ocean trenches
Oceanic and continental convergence. Oceanic crust subducted beneath continental crust, which forms the ocean trench. E.g. Peru-Chile trench
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Describe Composite (Acid) Volcanoes
Convergence. Alternating eruptions of ash, tephra and lava. Viscous lava can't flow far before cooling, creating steep-sided volcanoes/convex cones. E.g. Mount Pelee
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Describe Shallow-focus earthquakes
Conservative plate margins. Friction between moving plates causes stress to build from sticking. Energy released suddenly in the form of an earthquake. E.g. The Great San Francisco Earthquake
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Describe Oceanic Crust Destroyed
Oceanic and Oceanic and Oceanic and Continental convergence. Denser oceanic crust is subducted and melted in the Bleinoff Zone. E.g. Pacific Ring of Fire
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Describe Hot Spots and Basic Volcanoes.
Oceanic. Concentrated radioactive decay in the core generates hot spots, heating asnethosphere, creating localised thermal currents. Plumes of magma rise vertically and create basic volcanoes E.g. Hawaii
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Describe Shallow and Deep-focus earthquakes
Both Oceanic and Oceanic and Continental Convergence. Oceanic plate subducted, friction and sticking create a huge amount of pressure, plate slips and creates an earhquake.
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Describe Volcanic Islands
Oceanic Crust. Form from hot spots or submarine volcanoes.
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Current theory of Hot spots
Regions of superheating create stong convection currents and mantle plumes. Nearing the surface, the plume ancounters significantly lower pressures and becomes molten. Sometimes it pierces the crust above, where it coincides a crustal weakness.
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Weak Aspects of Hot Spot 'Proof' - Hawaiian Islands
Static Hotspots - classic explanation for bend in Hawaiian islands and Emperor Seamount chain is plate changed direction. However, modelling over time suggests this is not plausible and plume must have shifted.
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Weak Aspects of Hot Spot 'Proof' - Lithology
Analysis of Icelandic crust shows it formed in temperatures lower than expected in a superheated mantle plume
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Weak Aspects of Hot Spot 'Proof' - Depth of plume
Unsufficient evidence to show plumes emanate at core-mantle boundary
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Alternative theory of Hot Spot proof
All plates have scars from former collisions or divergence, and larger plates like the Pacific will be stretched towards the centre. When vulnerable crust pass over previously subducted slabs that melt easily in low-pressure, the stage is set.
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Hawaiian Islands
19, increase in size with distance. Kilauea erupting continuously since 1983. 30km offshore, Loihi Seamount promises to reach sea level in nest 100,000 years. Basaltic lava - 'aa' and 'pahoehoe'
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Hawaiian Islands
4000km from nearest continental landmass- perfect for astronomical and atmospherical observations. Mild tropical climate, very fertile soils. Extreme location means colonisation of new species took thousands of years. Highly adapted environment
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Hawaiian Islands tourism
65% domestic US tourism. Accounts for 25% of local economy, significant source of employment.
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Card 4

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Card 5

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Describe the Inner core.

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