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Geography > TECTONICS: Risk of Tectonic Hazards > Flashcards

TECTONICS: Risk of Tectonic Hazards Flashcards

1
Q

What do tectonic plates do?

A

move in different directions at different speeds - creating different types of plate boundaries

and therefore variations in earthquake and volcanic activity

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2
Q

Where are most earthquake and volcanic activity found?

A

Zones along plate boundaries

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3
Q

What plate boundary creates earthquakes with a magnitude of 9?

A

Destructive plate boundaries

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4
Q

What are Intra-plate earthquakes?

A

Earthquakes that do not happen at plate boundaries
- happen near the middle of plates

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5
Q

Are Intra-plate earthquakes high in magnitude?

A

No, they are associated with smaller magnitude earthquakes

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6
Q

What are Intra-plates often linked to?

A

Hot spots or old fault lines

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7
Q

Explain how volcanic activity can happen near the centre of some hot spots

A
  • tectonic plate moves over the plume leading to the formation of a chain of volcanic islands
    (e.g. Hawaii)
  • or from the top of a stationary large mantle plume just under the crust
    (e.g. Cape Verde Islands, African plate)
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8
Q

What can collisions of tectonic plates do?

A

fracture the crust well away from the plate boundary
(e.g. Himalayas)

-earthquakes can happen over long period of time as collisions slowly take place & movement is caused along faults

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9
Q

What are faults?

A

A fracture or zone of fractures between two blocks of rock

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10
Q

What’s a hotspot?

A

A large plume of hot mantle material rising from deep within the earth

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11
Q

What is convection and how is it created?

A

Convection is heat within the asthenosphere (upper mantle)

It’s created in the mantle and radiates outwards from the inner core

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12
Q

What’s in the mantle?

A

Viscous liquid that’s created by being under pressure due to depth

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13
Q

What is sea floor spreading?

A

Tectonic plates (large slabs of earth’s lithosphere) split apart from each other

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14
Q

What are the 3 causes of sea floor spreading?

A
  1. Convection currents
  2. Ridge push
  3. Slab pull
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15
Q

How do convection currents move tectonic plates? (older theory)

A

Occurs within the molten rockin the mantle, acts like a conveyor belt for the plates

  • friction between the convection current and the crust causes the tectonic plate to move (frictional drag)
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16
Q

How does ridge push move tectonic plates?
(newer theory)

A
  1. Magma rises as the plates move apart
  2. The magma cools to form new plate material
  3. As it cools It becomes denser and slides down away from the ridge
  4. This causes other plates to move away from each other
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17
Q

At which plate boundary does ridge push occur at?

A

Constructive

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18
Q

How does slab pull move tectonic plates?
(newer theory)

A
  1. The denser plate sinks back into the mantle under the influence of gravity
  2. It pulls the rest of the plate along behind it
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19
Q

At which plate boundary does slab pull occur at?

A

Destructive

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20
Q

What plate boundaries do volcanoes occur at?

A

Convergent & Divergent

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21
Q

What plate boundaries do the most powerful earthquakes occur at?

A

Convergent & Conservative

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22
Q

Where are 75% of volcanoes found?

A

Around the ‘Ring of Fire’ surrounding the Pacific Ocean

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23
Q

What are the 4 major types of plate boundaries?

A
  1. Destructive (convergent)
  2. Constructive (divergent)
  3. Collision (convergent)
  4. Transform (conservative)
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24
Q

What happens at Destructive (convergent) plate boundaries?

A

Plates move together or converge

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25
Q

What happens at Constructive (divergent) plate boundaries?

A

Plates move apart or diverge

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26
Q

What happens at Collision (convergent) plate boundaries?

A

Plates collide with each other

27
Q

What happens at Transform (conservative) plate boundaries?

A

Plates move parallel with each other

28
Q

What happens at Constructive (divergent) plate boundaries?

A
  1. Magma rises in mantle below, 2. cools off and spreads out
  2. some solidifies & creates new crust
  3. crust begins to slowly move apart (makes 2 separate tectonic plates)
    EXAMPLE: Mid-ocean ridges
29
Q

What hazards occur at Constructive (divergent) plate boundaries?
& describe what happens

A

Volcanoes:
- magma and some gases (e.g. carbon dioxide) melt through crust & are release through the surface LOTS OF LAVA!!

Earthquakes:
- are weak
- earthquakes happen when tectonic plates get stuck or grind against each other

BUT doesn’t happen often as plates are often moving apart

30
Q

What happens at Destructive (convergent) plate boundaries?
Continental + Oceanic

A

Plates move towards each other, and the oceanic plate subducts under the continental plate

31
Q

What hazards occur at a Destructive (convergent) plate boundary?
Continental + Oceanic
& describe what happens

A

Volcanoes: Violent volcanic eruptions
1. Oceanic is forced underneath (denser) by subduction
2. oceanic plate sinks into mantle & water/dead plankton on sea floor is dragged down with it
3. They are turned into water vapour & Carbon dioxide
4. Then they bubble up and melt through continental crust above (get trapped in the rock)
5. pressure builds (like shaking a fizzy drink)
6. Pressure gets too much
7. Gas & Lava violently explode out of rock (volcanic eruption)

Earthquakes: extremely powerful
1. extremely powerful
2. these huge slabs of rock continually grind against & get stuck on each other
3. when stuck, continental plate gets dragged down with oceanic plate
4. huge amounts of energy builds up
5. plates become unstuck and release all this stored energy
6. causes intense shaking of ground

32
Q

What happens at a Collision (convergent) plate boundaries?
Continental + Continental
& describe what happens

A
  1. Both plates have same density
  2. crash head on
  3. crumple upwards creating fold mountains
    EXAMPLE: Indian and Eurasian plates=The Himalayas
33
Q

What hazards occur at a Collision (convergent) plate boundary?
Continental + Continental
& describe what happens

A

NO VOLCANOES - no magma

Earthquakes:
1. plates grind and buckle upwards over millions of years
2. get locked together and stuck on each other
3. enough energy builds up and plates get unstuck
4. plates jult back into movement
(earthquake is created)

34
Q

What happens at Transform (Conservative) plate boundaries?

A
  • two tectonic plates slide past each other
  • opposite or same direction
  • different speeds
35
Q

What hazards occur at Transform (conservative) plate boundaries?
& describe what happens

A

NO VOLCANOES - no magma

Earthquakes:
1. edges of plates get stuck as they grind past
2. builds up energy
3. jolt back to moving again
4. energy is released causing ground to shake

36
Q

What happens in palaeomagnetism?

A

Mid-Ocean Ridge:
1. maga rises and solidifies on edge of crust
2. certain minerals in rocks ‘lock-in’ a record of the direction of Earth’s magnetic field
3. results in a series of magnetic strata with rock aligned alternately to N & S poles

37
Q

How does palaeomagnetism show plate movement?

A
  1. Striped pattern is mirrored exactly on either side of the ridge & Proves the magma from the spreading centre forms the plates
  2. The rock further away from the spreading centre is older and is a different polarity & Proves the movement of the plate, and the formation of new rock
38
Q

What is meant by the ‘focus’ of an earthquake?

A

The point at which the strain is released

  • sends earthquake (seismic) waves in all directions
  • strongest at the point on the Earth’s surface directly above the focus (epicentre)
39
Q

Which plate boundaries have the most stress and strain buildup along?

A

Destructive plate boundaries:
e.g. Wadati-Benioff zone (Japan)

Transform (conservative) boundaries
e.g. San Andreas Fault

40
Q

Which plate boundary has shallow focus;usually low magnitude (5-6)

A

Constructive (divergent)

41
Q

Which plate boundary has a range of focal depths from shallow to 700vkm along Wadati-Benioff zone; often high magnitude (8-9)

A

Destructive (convergent):
Ocean + Continental

42
Q

Which plate boundary has a range of focal depths from shallow to 700vkm along Wadati-Benioff zone; moderate to high magnitude (7-9)

A

Destructive (convergent)
Oceanic + Oceanic

43
Q

Which plate boundary has shallow to intermediate focal depth; moderate magnitude (6-8)

A

Collision (convergent)
Continental + Continental

44
Q

Which plate boundary has shallow focus; usually moderate magnitude (6-8)

A

Transform (conservative)

45
Q

Which plate boundary has effusive eruptions (low VEI scale 1-3)

A

Constructive (divergent)

46
Q

Which plate boundary has explosive (moderate to high VEI scale 5-6)

A

Destructive (convergent)
Oceanic + Continental

47
Q

Which plate boundary has explosive (moderate to high VEI scale 5-6)

A

Destructive (convergent)
Oceanic + Oceanic

48
Q

Which plate boundary has effusive eruptions (low VEI scale 1-3)

A
49
Q

Which plate boundary has effusive eruptions (low VEI scale 1-3)

A
50
Q

Which plate boundary has explosive (moderate to high VEI scale 5-6)

A

Destructive (convergent):
Ocean + Continental

51
Q

Which plate boundary has usually no volcanic activity?

A

Collision (convergent)
Continental + Continental

52
Q

Which plate boundary has usually no volcanic activity except for the occasional fissure eruptions?

A

Transform (conservative)

53
Q

What are the different types of earthquake (seismic) waves?

A

Primary (P waves)
Secondary (S waves)
Rayleigh wave
Love wave (L waves)

54
Q

Characteristics of Primary (P waves)

A
  • arrives first
  • short wavelength
  • travel quickly through the crust
55
Q

Characteristics of Secondary (S waves)

A

S waves - secondary
- longer wavelength
- velocity of 4 km/s
(causes more destruction)

56
Q

Characteristics of Rayleigh waves

A
  • only travels through surface of crust
  • travels in a rolling motion
  • ground is moved up and down & side to side
  • responsible for most of the shaking felt by people
57
Q

Characteristics of Love (L waves)

A
  • only travels through surface of crust
  • fastest of the surface waves
  • moves from side to side as it moves forwards
58
Q

In november 2011, what happened in Japan
(In terms of earthquake seismic waves)

A

In Tohoku, Japan the S waves reached Tokyo 90 seconds after the release of stress at the focal point

59
Q

What are secondary hazards?
& give an examples

A
  • The indirect effects caused by the primary impact after the main event

Examples:
- Tsunamis
- Landslides
- Liquefaction

60
Q

How do Landslides occur

A

The movement of the Earth may loosen rock or trigger the collapse of unconsolidated material down steep slopes

  • have possible consequences e.g. may hit property’s, block or destroy roads, etc
61
Q

How does Liquefaction occur

A
  • occurs in lowland areas
  • shaking sorts the ground material to the point where it acts as a fluid
62
Q

How can Tsunamis be caused by earthquakes?

A
  1. may occur if an earthquake happens beneath the sea bed
  2. As the sea bed jolts water is displaced and forced upwards creating a wave
  3. As the wave approaches the land they slow and the wavelength becomes compressed
  4. leads to an increase in wave height: they frequently reach 5-10 meters, but can reach 30 meters
  5. As the wave reaches shore a vacuum is created and the water recedes rapidly out to sea leaving the sea bed exposed
63
Q

What else can Tsunamis be caused by?

A
  • Landslides which may be due to earthquakes and volcanic eruptions displacing the water
  • Underwater volcanic eruptions

Geography (13 decks)

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