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physical geography > plate tectonics > Flashcards

plate tectonics Flashcards

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1
Q

What is the earths structure

A

Core
Mantle
Crust
Lithosphere

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2
Q

What elements are in the crust

A

Silicon, oxygen, aluminium, pottasium

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3
Q

How thick is the crust below the ocean

A

6-10km

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4
Q

How thick is the crust below land

A

30-40km

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5
Q

How thick is the lithosphere

A

60-70km

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6
Q

What are the two types of crust

A

Continental and oceanic

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7
Q

Which type of crust is denser

A

Oceanic

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8
Q

What is the composition of continental crust

A

Mainly granite, silicon,aluminium and oxygen

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9
Q

What is the composition of oceanic crust

A

Basalt, silicon,magnesium and oxygen

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10
Q

How do the plates move

A

Convection currents which push and pull the plates

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11
Q

What was Alfred wegeners theory of tectonic

A

That tectonic plates have evolved from pangea, 300 million years ago

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12
Q

How is sea floor spreads evidenced

A

Examination of the oceanic crust either side of the mid Atlantic ridge (alternating polarity of magnetic rock)

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13
Q

What create thermal convection currents

A

Hot spots in the mantle

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14
Q

Biological evidence for continental drift

A

-Fossil remains of mesosaurus in Brazil and South Africa
-fossil brachiopods found in Indian limestone and Australia
-fossil remains of plant which existed when coal was being formed found in India and Antarctica (coal only forms in tropical conditions)

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15
Q

Evidence for continental drift- climatology

A

Evidence of glaciation found in South America and India

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16
Q

Evidence for continental drift- geology

A

Rocks of similar age,formation and structure found in Brazil and South Africa
Coal sandstone and limestone could not have been formed in Britain with its current climate

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17
Q

Palaeomagnetism

A

In underwater eruptions basaltic lava cools
Rock aligns with earths magnetic field
This is reversed every 400,000 years
Bands of rock facing different poles are formed

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18
Q

Constructive margins occurs where

A

Two plates move away from eachother

19
Q

What do constructive boundaries form

A

Rift valleys
Mid oceanic ridges

20
Q

Volcanic activity at constructive boundaries

A

Gentle slides
Basaltic lava
Gentle eruptions
Frequent
Effusive

21
Q

Transform faults

A

Occur at right angles to boundary as new crust is formed
Friction and earthquakes )shallow focused)

22
Q

Rift valleys

A

-form when plates move apart on continental areas
-areas of crust drop down parrallel faults
-forms an upstanding block known as a horst
-in east african rift valley it is said to be an emergent plate boundary and forming a new ocean

23
Q

Example of rift valley

A

East African rift valley
Extends for 5000km from Mozambique to the Red Sea and Jordan
Width varies from 10-50km

24
Q

Conservative plate margins occur when

A

Two plates move past eachother

25
Q

What hazards occur at conservative margins

A

Earthquakes only

26
Q

Example of conservative margin

A

San Andreas fault in california

27
Q

Destructive margins occur when

A

Two plates move towards each other and the heavier plate sinks beneath the lighter plate

28
Q

Example of destructive margin

A

Andes, west coast of South America
Nazca plate subducts under South American plate
Molten magma rises forming explosive volcanoes

29
Q

What are island arcs and how are they formed

A
  • subducting plate becomes hot
    -pressure and friction melts the plate
    -rises to the surface as a pluton of magma
    -composite volcano islands are formed
30
Q

Where are fold mountains formed

A

-Destructive continental and continental boundaries
-there is no subduction
-edges and sediments are forced upwards
-there is no volcanic activity
-indo-australian plate travelling nirthwards into eurasian
-formed the himalayas

31
Q

How do fold mountains form

A

Lower density continental courts collide
Plate edges forced upwards
No subduction so no volcanic activity e.g. the Himalayas

32
Q

Hotspots

A

Areas on the crust of volcanic activity that are not related to hazards

33
Q

What do hot magma plumes do

A

Burn through weaker parts of the crust and states in the same plates as the plate moves

34
Q

Hawaiian chain of volcanic islands facts and figures

A

60° bend in the shape of the islands
3,700 miles long
Travelling NW
Are getting eroded
Up to 5 million years old

35
Q

What does Tuzo Wilson say creates magma plumes

A

Static radioactive elements

36
Q

What does Foulger 2003 suggest forms hotspots

A

Weakness in tectonic plates
Faults in the crust allow plume of magma through

37
Q

What is a mantle plume

A

A pocket of magma which has melted through the asthenosphere from the core due to static radioactivity

38
Q

What is the most common rock type formed by the eruption of Hawaiian volcanoes

A

Basaltic rock (low silica and low gas content)

39
Q

ocean ridges

A

longest continuois uplifted features
when plates move apart in oceanic areas
space is filled with basaltic lava, cools and forms magnetic rock
volcanic acitivity - submarine volcanoes

40
Q

deep sea trenches

A

where oceanic and continental plates move
denser plate subducts
nazca under south american
formed peru-chile trench

41
Q

island arcs

A

during subduction the descending plate enters hotter surroundings generated by frcition
begins to melt the plate
material is less dense and rise towards surface as plutons of magma
eventually reach surface and form compositive explosive volcanoes

42
Q

Sea floor spreading theory

A

After discovery of mid Atlantic ridge
Altenratating polarity of the rocks - iron/magnetic particles in erupted lava
Poles reverse every 400,000 years
Results in magnetic stripes that are aligned to the poles
Oceanic crust gets older with the distance from the ridge

43
Q

Ridge push / gravitational sliding

A

Constructive boundaries
Upwelling of hot material at ocean ridges - creates buoyancy effect
Plates experience force that acts away from the ridge
Gravity acting down the slope of the ridge

44
Q

Slab pull

A

Destructive boundaries
Downward gravitational force on the cold dense decending plate
Pills the whole oceanic plate down as a result of negative buoyancy
Frictional resistance - gives rise to shallow and deep earthquakes

physical geography (28 decks)

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