Tectonics

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What is an intra-plate process?
Middle of plates, associated with ancient faults such as the Rhine Rift Valley in Africa which resulted from the solid crust craxking over millions of years or collisions of plates- associated with smaller magnitude earthquakes
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What is a hot-spot?
Volcanic activity near the centre of plates- either the result of the upwelling of hot molten material from the core e.g. Hawaii or from the top of a large mantle plume under the crust e.g. Cape Verde Islands or rarely, large meteorite impacts
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Explain the convection of the mantle
Convection is created in the mantle by heat radiating outwards from the inner core. Mantle material, mostly peridodite is under pressure and when heated behaves like a viscous liquid- this has been proved by the Rayleigh-Bernard theory
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Why is the mantle complicated?
Multiple layers with density and mineral differences so it has been suggested that there could be convection in thw whole mantle or several layers of convection - there is also a pattern of hot and cold areas
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How can you measure and find out about the interior of the earth?
By the use of seismic waves which travel through the solid and liquid layers of the earth
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What is the mineral compostion of the earth?
Includes olivine and helium
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What happens when the mantle convection cells make contact with the base of the crust?
They move the plates by frctional drag
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What may subduction do to the mantle?
If the mantle is subducted at cold downdwellings, it may cause slab pull and may cuase the location of cooler mantle areas and the downward movement within the convection current
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Why may lots of subduction around the edge of the pacific plate cause the plate to move faster?
The downdwellings and cold areas of created by the subduction will lead to the down movement of the convection current and therefore move the plates by slab-pull
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Where is this evident?
Scotland and North America
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How thick is the crust?
Oceanic = up to 7km and continental = up to 70km
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How dense is the crust?
Oceanic = less at 2.7g/cm3 Continental = more at 3.3g/cm3
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What is the composition of the crust?
Continental= granite and Oceanic = basalt
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Can seismic waves pass through?
Surface and body waves are able to pass through
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What is the temperature of the crust?
Up to 400 degrees celcius
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How deep is the mantle?
700-2890km
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How hot is the mantle?
870 degrees celcius
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What is the density of the mantle?
Low to medium - 3.3-5.4 g/cm3
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What is the composition of the mantle?
Peridodite + upper = olivine and lower = magnesium silicate
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What is the physical state of the mantle?
Solid and liquid areas
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Can seismic waves pass through?
Body waves pass through at variable rates due to density changes
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How deep is the outer core?
2890-5150km
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How hot is the outer core?
4400-6100 degrees celcius
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How dense is the outer core?
Dense
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Composition of the outer core?
12% sulphur and 88% iron
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Physical state of the outer core?
Liquid and generates magnetic field
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Can seismic waves pass through?
Only P waves, and S wave shadow zone is created from just over a 100 degree focal point
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How deep is the inner core?
5150km
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How hot is the inner core?
7000 degrees celcius (radioactive decay)
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Is the inner core dense?
Very dense
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What is the composition of the inner core?
20% nickel and 80% iron
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Can seismic waves pass through?
Only P waves reach the inner core and pass through
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Characteristics of a Destructive Subductive plate boundary?
Range of focal depths from shallow to 700km along the Wadati-Benioff zone, often high magnitude (8-9), explosive, moderate to high VEI (5-6), Island arcs, oceanic trenches, back +fore arc, low heat flow, negative gravity anomaly, range of rock age
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Characteristics of Destructive Collision? (ocean ocean)
Range of focal depths from shallow to 700km along the Wadati-Benioff zone, often high magnitude (7-9), explosive VEI (5-6), Island arcs, ocean trenches, back and fore arc zones, low heat flow, range of rock age, negative gravity anomaly
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Characteristics of Divergent Constructive?
Shallow focus, usually low magnitude (5-6), effusive eruptions -low VEI scale (1-3), ocean ridge with central rift valley, faulting at right angles, volcanic islands, high heat flow- young baltic rock
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Characterstics of a convergent collision? (continent continent)
Shallow to intermediate focal depth, moderate magnitude (6-8), usually no volcanic activity, fold mountains and plateaus, average heat flow, variable rock age
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Characteristics of a Transformative Conservative?
Shallow focus, moderate magnitude (6-8), occasional fissure eruptions,ridges and scars on surface, average heat flow, rock age depends on oceanic or continental location
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Who are the 3 individuals associated with Plate Tectonic Theory?
Sir Francis Bacon (1620)- jigsaw idea, Benjiman Franklin (1700s)- egg shell theory, Alfred Wegner (1912)- continental drift, Harry Hess (1948) - sea floor spreading
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What is the evidence for Plate Tectonic Theory?
Paleomagnetism, climatological, biological, geological
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What is the Wadati- Benioff zone?
planar zone of seismicity corresponding with the down-going slab in a subduction zone. Differential motion along the zone produces numerous earthquakes, the foci of which may be as deep as about 670 kilometres
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Whatn are the 4 seismic waves?
Primary, Secondary, Raleigh + Love
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What are the characterstics of the Primary wave?
Arrives first, fast, moves through solid rock and fluids, pushes and pulls (compresses) in direction of travel
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What are the characterstics of the Secondary wave?
Second wave, slower than P wave, only moves through solid rock, up and down movement
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What are the characterstics of the Raleigh wave?
Only travels through the surface of the crust, rolling motion, ground moved up, down + side to side- responsible for most of what is felt by people
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What are the characterstics of the Love wave?
Only travels through the surface of the crust, fastest wave, moves side to side as it moves forward
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What are secondary hazards?
Tsunamis, landslides, liquefaction etc.. anything that is caused by an earthuake
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Explain the characterstics of tsunamis
Major secondary hazard because of their potential for destructive ability + spacial area they can cover. Deep sequence of waves with deep troughs underneath them, water drawn upwards into each wave. The waves build height when they reach the shore
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Why do tsunami waves only reach height at the shore?
Friction at the base slows the waves down, shortening the wavelength and allowing them to build in height
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What are tsunamis caused by?
Water column displacement, undersea plate movement - displaces and thrusts up or down quickly or by underwater landslides such as at continental shelf edges
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How do you measure tsunamis?
Tsunami Intesity Index
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How long did it take for the Tokhuku tsunami to cross the Pacific Ocean?
22 hours, in a complex pattern due to refraction and reflection due to islands and land masses and the bathymetry of the ocean
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What does intensity depend on?
Land uses, population density, warning systems
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What does the run-up depend on?
Distance travelled, offshpre bathymetry, coastline orientation, extent of lowland, shape of coastline
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Why do volcano types differ?
They reflect the amount of enery released during an eruption
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Name 2 supervolcanoes
Taupo, New Zealand and Yellowstone, USA
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What are the characterstics of supervolcanoes?
Large calderas, long time periods between eruptions, significant eruptions- Yellowstone 2.1 mya was 6000x larger than Mt St Helens
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What is the shape of volcanoes related to?
The type of lava erupted
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What are the three main types of lava?
Rhyolitic, Basalt and Andesite
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What are the characterstics of basaltic lava?
Hottest (1000-1200 degrees celuis), low gas content, formed by melting of mantle minerals in upper zone, thin and runny flow, low viscosity -gases escape, gentle eruptions, shield volcanoes
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What are the characterstics of Rhyolitic lava?
Coolest (650-800 degrees celcuis), 4-6% gas content, formed by melting of lithospheric mantle and subducted plate, thich and stiff- high viscosity, very violent eruptions, supervolcanoes
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What are the characterstics of Andesitic lava?
800-1000 degrees celcuis, 3-4% gas content, formed by subducted plate melting and mixing with seawater + other continental rocks, slow flow + moderate-violent eruptions, composite cones, subductive zone
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What is a jokulhlaup>?
Flood of meltwater issuing from underneath and ice cap or glacier- happens when volcano erupts underneath the ice and melts ice so it forms lake in crater and will eventually spill out causing a flood due to it being warmer water melting the ice
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What is pyroclastic flow?
Dense mixture of superheated tephra and poisonous gases moving rapidly down the side of composite cones
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What is tephra?
rock fragments and particles ejected by a volcanic eruption- Eyjafjallajokull
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Evaluate the production of volcanic gases
Water vapour = most common- geysers etc.. sulphur dioxide- can cause acid rain or the cooling of the earth as the particles reflect the light e.g. Mount Pinatubo produced 20 million tonne Sulfur diox cloud and cooled the earth by 0.6 degrees c for 3
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Carry on
years.. CO2= would take 700 large eruptions a year to meet anthropogenic levels, fluorine gas- can contamine water and food
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What are lahars?
Water mixed with volcanic deposits flowing rapidly along existing valleys -dangers= fast velocity and large amounts of material carried and the great distances they can travel
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What happened with the Armero lahar in Colombia?
Nevado del Ruiz - killed 23,000 as it came in 2.5 hrs -pyroclastic flow melted 10% of the snow and ice cover on volcano, travelled at 60km/hr and travelled 100km - in places was 50m deep
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Card 2

Front

What is a hot-spot?

Back

Volcanic activity near the centre of plates- either the result of the upwelling of hot molten material from the core e.g. Hawaii or from the top of a large mantle plume under the crust e.g. Cape Verde Islands or rarely, large meteorite impacts

Card 3

Front

Explain the convection of the mantle

Back

Preview of the front of card 3

Card 4

Front

Why is the mantle complicated?

Back

Preview of the front of card 4

Card 5

Front

How can you measure and find out about the interior of the earth?

Back

Preview of the front of card 5
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