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Geography > Tectonic Hazards 1 > Flashcards

Tectonic Hazards 1 Flashcards

Plate tectonics, earthquakes and volcanoes, living in areas at risk from tectonic hazards.

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1
Q

What are the two layers of the core?

A

-Inner metallic core (solid)
-Outer core (liquid)

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2
Q

What are the layers of the earth called?

A

-Core (hottest part)
-Mantle (consists of semi-molten rock)
-Crust (thin outer ‘shell’)

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3
Q

The Earth’s crust is divided into what?

A

Large slabs called tectonic plates which float on the mantle.

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4
Q

What are tectonic plates made up of?

A

Two types of crust: Continental and Oceanic.

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5
Q

Continental crust

A

Thicker (30-50km) and less dense.

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6
Q

Oceanic crust

A

Thinner (5-10km) and denser.

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7
Q

Why do tectonic plates move?

A

Tectonic plates move due to convection currents in the mantle.

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8
Q

What are convection currents?

A

Circular movements of semi-molten rock.

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9
Q

What do we call the place where tectonic plates meet?

A

Plate margins/Plate boundaries

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10
Q

What is a plate margin?

A

A boundary between tectonic plates (which may be moving together, apart, or alongside each other).

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11
Q

What is the first step in how convection currents are formed?

A
  1. Radioactive decay of some of the elements in the core and mantle generates a lot of heat.
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12
Q

What is the second step in how convection currents are formed?

A
  1. When lower parts of the mantle molten rock (magma) heat up, they become less dense and slowly rise.
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13
Q

What is the third step in how convection currents are formed?

A
  1. As they move towards the top of the mantle layer (nearer to the lithosphere), they cool down, become more dense, and slowly sink.
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14
Q

What are the features of a constructive plate margin?

A

-Mid -ocean ridges
-Rift valleys
-Gentle earthquakes
-Shield volcanoes (gentle eruptions)

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15
Q

What is the fourth step in how convection currents are formed?

A
  1. These circular movements of semi-molten rock are known as convection currents.
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16
Q

What is the fifth and final step in how convection currents are formed? (hint: what do they do next?)

A
  1. Convection currents create drag on the base of tectonic plates, and this causes them to move.
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17
Q

What are the 4 types of plate margin?

A

-Constructive
-Destructive
-Conservative
-Collision

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18
Q

Constructive plate margins

A

Two plates diverge away from each other. Magma rises to fill the gap and eventually cools, forming new crust.

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19
Q

Example of a constructive plate margin

A

The Eurasian plate and the North American plate are moving away from each other, forming the Mid- Atlantic ridge.

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20
Q

Destructive plate margin

A

Two plates converge towards each other. When these are different types, (oceanic and continental) the denser oceanic plate is subducted into the mantle where it is destroyed, creating gas-rich magma. Magma is pushed to the surface, forming volcanoes.

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21
Q

Features of a destructive plate margin

A

-Ocean trenches
-Strong earthquakes
-Composite (explosive) volcanoes (violent, unpredictable).

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22
Q

Example of a destructive plate margin

A

Along the west coast of South America, the oceanic Nazca plate is being subducted beneath the continental South American plate, creating the Atacama trench.

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23
Q

Collision plate margin

A

Plates of a similar density meet (usually continental). They collide, causing the ground to become crumpled and uplifted. This is how the Himalayas were formed.

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24
Q

Features of a collision plate margin

A

-Crumple zone
-Fold mountains
-Earthquakes

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25
Q

Conservative plate margin

A

Two plates move sideways past each other, or move in the same direction but at different speeds (creating friction!) Crust isn’t created or destroyed.

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26
Q

Example of a conservative plate margin

A

At the San Andreas fault, USA, the Pacific plate is moving in the same direction as the North American plate, but faster.

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27
Q

Where do earthquakes occur?

A

Along all plate margins. (as all involve tension building up).
Some can occur in the middle of plates.

28
Q

Why do earthquakes occur?

A

Due to the build up and sudden release of pressure. This pressure (stress) is typically caused when two plates become locked, causing friction to build up.

29
Q

What are seismic waves?

A

A form of energy that travels through the crust (from the focus to the epicentre) when pressure is suddenly released. This causes the crust to vibrate, triggering an earthquake.

30
Q

What is an earthquake?

A

A severe shaking of the ground.

31
Q

Where do volcanoes occur?

A

Constructive and destructive plate margins.
Some also form over hotspots (parts of the mantle which are really hot) e.g in Hawaii.

32
Q

How do volcanoes form at constructive plate margins?

A

Magma rises up into the gap created when the plates diverge away from each other, forming a volcano.

33
Q

How do volcanoes form at destructive plate margins?

A

Denser oceanic plate is subducted into the mantle where it is destroyed, creating gas-rich magma. Magma rises to the surface through cracks in the crust called vents. The magma (called lava once it reaches the surface) erupts, causing a volcano.

34
Q

Why are volcanoes and earthquakes classed as tectonic hazards?

A

They are caused by the movement of the Earth’s crust.

35
Q

What happens when a volcano erupts?

A

-It emits lava and gases
-Some emit ash, which can cover land, block out the sun, and form pyroclastic flows.

36
Q

Pyroclastic flows

A

Super- heated currents of gas, ash, and rock.

37
Q

Pacific ring of fire

A

The high concentration of volcanoes found around the Pacific plate margin.

38
Q

How does tension build up on destructive plate margins?

A

One plate gets stuck as it moves past the other.

39
Q

How does tension build up on constructive plate margins?

A

Along cracks in the plates as they move away from each other.

40
Q

How does tension build up on conservative plate margins?

A

When plates that are grinding past each other get stuck.

41
Q

Why might people choose to live in areas at risk from tectonic hazards?

A

-If they don’t have a choice because they are too poor to move
-They don’t know the risks
-They and their families have always lived there
-Confidence in government and infrastructure
-Fertile soils from volcanic ash
-Geothermal energy
-Tourism industry/ports

42
Q

Living in areas at risk from tectonic hazards for farming.

A

The minerals from volcanic ash make the soil around volcanoes very fertile.

This means that farmers can benefit greatly: as these fertile soils provide plants with the nutrients they need to grow, this means that the farmers can make a good income to support their livelihoods.

For example, Kenyan coffee is grown on fertile volcanic soil, which makes it taste rich but also means that the farmers here can afford to grow coffee beans without the need to buy expensive fertilisers.

43
Q

Living in areas at risk from tectonic hazards for geothermal energy.

A

Fault lines found at tectonic plate boundaries allow water from underground supplies to reach the surface.

This means that hot water and heating can be provided using geothermal energy, which means that a country and its people can save money as geothermal energy is a cost effective, sustainable source.

For example, in Iceland , 90% of building are heated this way.

44
Q

Living in an area at risk from a tectonic hazard - tourism.

A

Volcanoes are tourist attractions. This means lots of people live nearby to work in the tourism industry. For example, Mount Etna, Italy, receives hundreds of thousands of visitors when its erupting.

45
Q

Living in an area at risk from a tectonic hazard - confidence.

A

In higher income countries, e.g. Japan, monitoring and warning systems are often put in place.

This means that the people living in these areas should get advanced warnings about a natural hazard that will occur, which means they have time to prepare and decide to evacuate if needed, minimising the risk of the hazard.

Furthermore , many people in these wealthier countries trust their government will support them in recovery from a hazard. For example, after Mt Etna erupted in 2001, the Italian government provided tax breaks and other financial aid.

46
Q

What are the four main management strategies that can reduce the effects of tectonic hazards?

A

-Monitoring
-Prediction
-Protection
-Planning

47
Q

What are the ways to monitor?

A

-Seismicity (earthquakes)
-Remote sensing
-Ground deformation
-Gas measurements
-Hydrology
-Geophysical measurements
-Physical signs like fractured rocks or steam eruptions.

48
Q

Seismicity (earthquakes)

A

Seismometers are used to record seismic energy in the Earth’s crust, and can be used in early warning systems to give a small but vital amount of warning before an earthquake occurs.

49
Q

Remote sensing

A

Satellites detect heat and changes to the shape of a volcano.

50
Q

Ground deformation

A

Changes to the shape of a volcano are measured using laser beams.

51
Q

Gas measurements

A

Scientific instruments are used to detect gases released as magma rises (a change in gas levels would indicate a potential eruption). Hydrology follows the same idea, but measures gases dissolved in water.

52
Q

Geophysical measurements

A

Detecting changes in gravity as magma rises.

53
Q

Detecting changes in a volcano’s shape may help to predict an eruption because…

A

…as magma rises before an eruption, the volcano is likely to swell.

54
Q

Can earthquakes be predicted?

A

No, but scientist can forecast when they might occur by monitoring the movement of tectonic plates.

55
Q

Can volcanoes be predicted?

A

Yes, if scientists monitor volcanoes closely. Predicting a volcanic eruption gives people time to evacuate.

56
Q

How can we protect buildings from earthquakes?

A

Make them ‘earthquake resistant’

57
Q

How can we make buildings ‘earthquake resistant’?

A

-Reinforce walls with concrete
-strengthen buildings and doors with steel frames
-Rolling weights on roofs
-Shock absorbers
-Automatic shut off switches

58
Q

Why do we reinforce walls with concrete?

A

So they absorb an earthquake’s energy (shock waves)

59
Q

Why do we strengthen buildings and internal structures with steel frames?

A

So they are less likely to collapse.

60
Q

Why might we build rolling weights of roofs?

A

To counteract shock waves.

61
Q

What do shock absorbers do?

A

Absorb earthquake energy in the foundations of a building.

62
Q

Automatic shut-off switches

A

Turn off gas and electricity supplies to prevent fires.

63
Q

Open areas

A

People can assemble here during an evacuation.

64
Q

Protection from volcanic eruptions

A

Earth embankments have been used to try to divert lava away from settlements, but with little success.

65
Q

HOW do management strategies reduce the effects of tectonic hazards?

A

By reducing the number of people killed, injured, homeless, or left unemployed.

66
Q

Planning methods

A

Similar methods are used to plan for earthquakes and volcanic eruptions.

67
Q

Methods used to plan for earthquakes and volcanic eruptions:

A

-Future developments can avoid high risk areas
-Emergency services can prepare e.g. practicing rescuing people from collapsed buildings
-People can be educated so they know what to do in the event of a hazard
-Governments can plan evacuation routes to get people away quickly and safely
-Emergency supplies like blankets, clean water, and food can be stock-piled.

Geography (18 decks)

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