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Physical Geography > Plate Tectonics > Flashcards

Plate Tectonics Flashcards

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1
Q

Earth structure:

Describe the core

A
  • 2900km down to the centre
  • densest part of the planet
  • made of rocks rich in iron and nickel
  • semi-molten outer core and solid inner core
  • can reach 5000*
  • generates convection currents
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2
Q

Earth structure:

Mantle

A
  • bottom of the crust down- 2900km
  • surrounds core, silicate rocks rich in iron and magnesium
  • most is semi-molten up to 3800*
  • density increases as you go down
  • generate convection currents
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3
Q

Earth structure:

Crust

A
  • thinnest layer
  • made of the coolest, less dense rocks
  • rich in silicon, oxygen amd aluminium
  • oceanic: thin, young basalt rocks and 5-10km in thickness
  • continental: thick, old and up to 70km thick
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4
Q

Plate tectonic theory:

Who came up with it and describe it

A

1912 Alfred Wegener

  • all continents were once joined together in a super continent called Pangea
  • at some time the land masses had drifted apart until they occupied their current positions
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5
Q

What is some of the evidence for continental drift

A
  • jigsaw fit: some continents seem to fit together if placed side by side eg. Africa and South America
    -geological evidence: rocks of the same age and type found in SE Brazil and South Africa
    _ trends in mountains like E Canada and NW Scotland are similar
    -biological evidence: similar fossil formations found either side of Atlantic
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6
Q

How tectonic theory developed:

A
  • W theory unable to explain how continents move
  • 1940 improvements in rock and fossil dating
  • 1950 nuclear submarines began monitoring and mapping ocean floors- mid Atlantic ridge was discovered
  • 1962 Harry Hess updated w theory.
  • studied rocks found youngest in the middle and oldest on the outside
  • At,antic sea floor was spreading outwards from the centre- 5cm a year
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7
Q

Evidence for sea floor spreading

A
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8
Q

Issue of sea floor spreading

A
  • implies the earth is getting bigger
  • not the case- plates must be getting destroyed somewhere
  • found this with huge ocean trenches
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9
Q

What is an ocean trench

A
  • large areas of the ocean floor being pulled down
  • subduction provides the mechanism
  • denser oceanic crust is created in some areas and destroyed in others
  • continental crust is not consumed
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10
Q

What are convection currents

A
  • higher temperatures at the earths core and heat released by radioactive decay creates them
  • more liquid magma which creates a continuous circulatory motion
  • causes plates to move
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11
Q

Major plate boundaries

A
  • seven major plates
  • all moving at different speeds and at different directions
  • over 50 plates
  • move on average 5-10 cm a year
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12
Q

Tectonic plates:

Continental

A

-over 1500 million years old
-permanent
-will not sink
-low density
-

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13
Q

Tectonic plates:

Oceanic

A
  • less than 200 million years old
  • denser
  • continually being formed sat ocean ridges
  • and continually being destroyed
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14
Q

Tectonic plates:

Facts

A
  • driven by slow moving convection currents within the mantle
  • can move in any direction
  • cannot overlap their boundaries so must either push past, be pushed upwards or downwards
  • no gaps can occur
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15
Q

Landforms associated with constructive margins:

A
  • Two plates separate to form a constructive margin
  • Oceanic areas: sea floor spreading occurs on either side of mid-oceanic ridge: mid Atlantic ridge
  • continental areas: stretching and collapsing the crust creates rift valleys: great African Rift Valley
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16
Q

Mid-oceanic ridges

A
  • oceanic ridges are long continuous uplifted features
  • total length of 60000km
  • regular breaks are transform faults
  • middle of ridges are deep valleys
17
Q

What are rift valleys

A 
-two plates pull apart 
Weaker zone in the crust and an increase in heat towards the surface 
Hotter expanded crust forms a ridge 
Central part may form a valley 
Great African Rift Valley
18
Q

What is constructive margin

A

When two plates separate

19
Q

What are submarine volcanoes

A

Split in the crust a lower pressure zone created where more liquid lava can erupt
Associated with constructive margins

20
Q

What are transform faults

A

New crust forms and spreads causes transforms faults at a right angle to the plate boundary
Spreading plate on either side moves at different rates

Leading to friction and earthquakes

21
Q

Three types of convergent margin

A

Oceanic and continental

Oceanic and oceanic

Continental and continental

22
Q

What happens at a oceanic and continental plate boundary

A

Denser oceanic plate forced under lighter continental plate
Subduction deep trenches can be found
Fold mountains

23
Q

What are deep trenches

A

Found along seaward edge of destructive margins
Marks where one plate begins to descend
Peru chile trench
Found at destructive plates

24
Q

What are fold mountains

A

Sediments accumulate on the continental shelf
Where land mass are deformed from folding and faulting
Along edge of continental plate which are uplifted
Andes
Found at destructive margins

25
Q

What is the Benioff zone

A

When oceanic plates begin to melt into magma on part of the subduction zone

26
Q

What is a destructive margin

A

When a oceanic plate sinks under a continental plate

27
Q

Oceanic and oceanic

A

Destructive margin
Two oceanic plates collide resulting in the denser one being sub-ducted
May be because it’s slightly denser or moving faster
Oceanic trenches and island arcs formed

28
Q

Continental and continental

A

Lower density - not much subduction
Plates move towards each other they are forced up into fold mountains
Little subduction so no volcanic activity
Shallow focus earthquakes
Material forced downwards to form deep mountain roots

29
Q

Conservative margin

A

Two crusts slide past each other

30
Q

What happens at constructive margins

A 
No creation or destruction 
No subduction- no volcanic activity 
Creates stress between plate edges 
Shallow focus earthquakes 
San Andreas fault 
Both moving in the same direction but not at same speed 
Transform faults
31
Q

Hot spots

A

Islands with volcanoes not connected with any plate boundary
Volcanic area created by a hot spot
‘A concentration of radioactive elements inside the mantle’
Plume of magma rises to eat into the plate above
Lava breaks through- active volcanoes
Stationary

32
Q

Island arcs

A

Hot spot stationary
Pacific plate moves over and lime of volcanoes is created
One above hot spot is active
Rest from a chain of extinct volcanoes

Physical Geography (3 decks)

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