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Geography > The Restless Earth > Flashcards

The Restless Earth Flashcards

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0
Q

What is a plate?

A

A section of the earths crust.

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1
Q

What is the crust?

A

Outer layer of the earth.

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2
Q

What is a plate margin?

A

The boundary where 2 plates meet.

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3
Q

What is the mantle?

A

The dense, mostly solid layer between the outer core and the crust.

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4
Q

What are convection currents?

A

Rising hot currents in the mantle that create movement and determine which direction the plates move in.

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5
Q

What is the difference between oceanic crust and continental crust?

A 
Oceanic crust is:
Newer.
Denser.
Can sink.
Can be renewed or destroyed.
Continental crust is:
Older.
Less dense.
Cannot sink.
Cannot be renewed or destroyed.
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6
Q

What is a constructive plate margin?

A

Where the plates move apart. Cracks and fractures form between the plates where there no solid crust. Magma rises up to the surface and new land is formed.

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7
Q

What do constructive plate margins form?

A

Lava flows and very shallow sided volcanoes. The volcanoes are not very explosive or dangerous. Ridges are built up from the sea bed because so much magma is poured out. Small earthquakes may occur.

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8
Q

Give an example of a country on a constructive boundary.

A

Iceland on the mid-Atlantic ridge where the North American and Eurasian oceanic plates are pulling apart.

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9
Q

What is a destructive plate boundary?

A

When plates move together. If one plate is oceanic crust and the other is continental crust, the denser oceanic plate sinks under the lighter continental. This is known as subduction. The subduction zone is an oceanic trench. As the oceanic plate sinks there is great pressure and the oceanic crust is destroyed and it melts forming magma.

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10
Q

What happens at a destructive plate margin?

A

Magma may rise upwards causing volcanic eruptions and leading to the formation of cone shaped composite volcanoes. The sinking oceanic plate can stick to the continental plate and pressure will build up. When the plates finally snap apart, a lot of energy is released as an earthquake. The earthquakes are often devastating.
The lighter continental crust stays at the surface, but sediment becomes crumpled into fold mountains.

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11
Q

Give an example of fold mountains at a destructive plate boundary:

A

Andes mountains in Peru and Chile where the Nazca oceanic plate is subducted under the South American continental plate.

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12
Q

What is a collision plate margin?

A

A type of destructive plate boundary when two continental plates collide. The plates are pushed up forming forming fold mountains. Destructive earthquakes also happen on faults in collision zones.

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13
Q

Give an example of a fold mountain range on a collision plate margin:

A

The Himalayas where the Indian and Eurasian continental plates push into each other.

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14
Q

What happens at a conservative plate margin?

A

The plates slide past each other

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15
Q

Why do earthquakes occur at conservative plate margins?

A

As one plate is moving slightly faster than the other and in a slightly different direction, causing the plates to stick to eachother. The movement of the plates causes friction and pressure builds up along the fault. Eventually the build up of pressure gets too great and on plate jerks past the other. The sudden release of pressure causes an earthquake.

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16
Q

Give a example of a conservative plate margin

A

San Andreas Fault, California, USA where the North American and Pacific plate are sliding past each other.

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17
Q

What are fold mountains?

A

Large mountain ranges where rock layers have been crumpled as they have been forced together.

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18
Q

What is a geosyncline?

A

A large depression

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19
Q

How are fold mountains formed?

A

Rivers carry sediments which are deposited in geosynclines.

Over millions of years the sediments are compressed into sedimentary rocks.

The sedimentary rocks are then forced upwards into a series of folds by the movement of tectonic plates.

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20
Q

What is an anticline?

A

Upfold of folded rocks.

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21
Q

What is a syncline?

A

Downfold of folded rocks.

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22
Q

What is an overfold?

A

Where a fold has been pushed over on one side.

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23
Q

What are ocean trenches?

A

Deep sections of ocean, usually where an oceanic plate sinks beow a continental plate.

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24
Q

What is the continental shelf?

A

The shallow zone, less than 200m deep, off the coast.

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25
Q

What are the main opportunities in the continental shelf?

A

Fishing.

Oil and Gas.

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26
Q

What are the physical problems of high fold mountains?

A

Relief-high and steep (little flat land)
Climate-growing season is short
Soils-stony, thin and infertile
Accessibility-travel disrupted by rockfalls, large mountains and bad weather

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27
Q

What is a volcano?

A

A cone shaped mountain formed by surface eruptions from a magma chamber inside the earth.

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28
Q

What is lava?

A

When magma reaches the surface it is called lava. Lava is one of the products that can be thrown out of volcanoes.

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29
Q

Where do volcanoes form?

A

Where magma escapes through a vent- a fracture or crack in the earths crust.

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30
Q

Where do shield volcanoes form?

A

Constructive plate margins.

When plates move apart magma rises from the mantle to fill the gap.

31
Q

Give an example of a shield volcano:

A

Mauna Loa, Hawaii

Surtsey, Iceland

32
Q

What type of lava comes from shield volcanoes?

A

Lava with a low silica content. This means that is pours easily, is runny and flows long distances before cooling.

33
Q

Name some characteristics of shield volcanoes:

A

The cone has a wide base and gentle slopes.
It is made of lava only.
It has regular eruptions.
Lava pours out with little violence.

34
Q

Where do composite cone volcanoes form?

A

At destructive plate margins.

The denser oceanic plate is pushed below the lighter continental plate at a subduction zone. In the subduction zone, the plate forms a pool of magma. Great heat and pressure forces the magma up a crack where it erupts at the surface to form a volcano.

35
Q

Why is the lava from composite cone volcanoes more viscous than the lava from shield volcanoes?

A

Because the acid lava from composite cone volcanoes has a higher silica content. This mans that it is more viscous so it travels shorter distances before cooling.

36
Q

Why are the eruptions at composite cone volcanoes explosive?

A

Because after an eruption the vent becomes blocked with cooled magma, which leads to great pressure building up behind it. When the next eruption occurs the cooled lava is shattered into pieces creating molten boulders.

37
Q

Give some characteristics of composite cone volcanoes:

A

The cone is tall with a narrow base and steep sides.
It is made of alternate layers of ash and lava.
Its eruptions are irregular and often have long dormant periods.
The eruptions are very volatile and explosive.

38
Q

Give an example of a composite cone volcano:

A

Mt Vesuvius and Mt Etna, Italy
Mt St Helans, USA
Krakatoa, Indonesia

39
Q

Name some possible primary effects of a volcanic eruption:

A

People injured or killed.
Buildings, property and farmland destroyed.
Communications and public services disrupted.

40
Q

Give some examples of possible secondary effects of a volcanic eruption:

A 
Shortage of drinking water, food, shelter, medicine.
Spread of disease.
Economic probems.
Social problems.
Lahars.
Environmental problems.
41
Q

What is a Lahar?

A

A mudflow resulting from ash mixing with melting ice water.

42
Q

Give examples of possible immediate responses of volcanic eruptions:

A

Evacuation.
Emergency services deployed.
International emergency aid sent.

43
Q

Give examples of possible secondary responses for a volcanic eruption:

A

Rebuilding.

Redeveloping economic activities (tourism+farming).

44
Q

Why do people live near volcanoes?

A

Volcanic soil is very fertile
Tourism industry provides employment
Valuable minerals
Endless supplies of hot water can create geothermal power

45
Q

How do we monitor and predict volcanic eruptions?

A

Electronic tiltmeters-measure small changes in the profile of a mountain

Global Positioning Systems (GPS)- use satellites to detect movement

Changes in the earths temperature can be monitored on satellite images

We can look at past eruptions and predict the next

Land use zoning and hazard mapping

46
Q

Where do super-volcanoes occur?

A

At hotspots

47
Q

What is a hotspot?

A

A section of the Earths crust where plumes of magma rise, weakening the crust. They are away from plate margins.

48
Q

Why don’t super-volcanoes look like normal volcanoes? What do they look like?

A

They are large depressions called calderas, and are often marked by a rim of higher land around the edges.

49
Q

How are super-volcanoes formed?

A

When magma in the Earth rises into the crust from a hotspot but is unable to break through. Pressure builds in a large and growing magma pool until the crust is unable too contain the pressure. Cracks appear in the surface and gas and ash erupt form the magma chamber. The magma chamber collapses, forming a depression called a caldera

50
Q

What is a caldera?

A

A large depression, often marked by a rim of higher land around the edges.

51
Q

What happens in a volcanic winter?

A

Lower temperatures on Earth, due to less sunlight reaching the surface.

52
Q

In what ways do super-volcanoes differ to ordinary volcanoes?

A
  1. They are much bigger
  2. They emit huge amounts of material (at least 100km3 compared to 1km3 when Mt St Helens erupted)
  3. They do not have characteristic cone shapes
  4. They are large depressions called calderas
  5. They often have a rim of higher land around the edges
  6. They only occur at hotspots
53
Q

What is an earthquake?

A

The shaking of the earth and vibration of the crust due to movement of the Earths tectonic plates.

54
Q

At which boundary can earthquakes occur?

A

Any

55
Q

What is the Focus of an earthquake?

A

The point in the Earths crust where the earthquake originates. The shaking is worse on the surface if the focus is shallow.

56
Q

What is the epicentre of the earthquake?

A

The point at the Earths surface directly above the focus

57
Q

What are shockwaves?

A

Seismic waves generated by an earthquake that pass through the Earths crust

58
Q

How is the magnitude of an earthquake measured?

A

With a seismograph

59
Q

What is the Richter Scale?

A

The Richter Scale is used for measuring earthquakes based on scientific recordings of the amount of movement.

60
Q

What type of scale is the Richter Scale?

A

It is a logarithmic scale. This means that there is a 10 fold increase every time the scale increases by 1. For example an earthquake measured at 7, is 10 times stronger than the one measured at 6 and 100 times stronger than the one measured at 5.

61
Q

What is the Mercalli Scale?

A

It is used to indicate the intensity of an earthquake. It classifies the effects of an earthquake using Roman numerals from I-XXII. It takes into account the visible effects on the Earths surface, people and infrastructure based on a persons observation.

62
Q

How do the Mercalli valcus differ?

A

Based on the distance to the earthquake, with the highest intensities being around the epicentre.

63
Q

What are the general primary effects of an earthquake?

A

Collapsed buildings

People killed/injured

64
Q

What are the general secondary effects of an earthquake?

A

Fires
Tsunami
Landslides
Diseases dues to burst sewage pipes.

65
Q

What are the physical factors that would cause high levels of damage during an earthquake?

A

A high magnitude on the Richter Scale
Shallow focus
Sands and clays vibrate more

66
Q

What are the physical factors that would cause low levels of damage during an earthquake?

A

Low magnitude
Deep focus
Hard rocky surface

67
Q

What are the human factors that would cause high levels of damage during an earthquake?

A

High density of population
Residential area
Self-built housing
Lack of emergency procedures

68
Q

What are the human factors that would cause low levels of damage during an earthquake?

A

Low density of population
Urban area with open spaces
Earthquake proof buildings
Regular earthquake drills

69
Q

What are the 3 Ps of managing earthquakes?

A

Prediction, Protection and Preparation

70
Q

How do scientists attempt to predict earthquakes?

A

Watching animal behaviour
Foreshocks
Guesswork

71
Q

How do we try and protect buildings from earthquakes?

A

Computer controlled weights on the roof
Steel frames that can sway during earth movements
Fire resistant building materials
Automatic window shutters to prevent falling glass
Foundations sunk into bedrock, avoiding clay
Open areas outside where people can assemble in saftey
Roads to provide quick access for emergency services

72
Q

How do we prepare for erthquakes?

A

By organising activities and drills so that people know what to do in the event of an earthquake.

73
Q

What is a tssunami?

A

A special type of wave where the entire depth of the sea or ocean is set in motion by an earthquake which displaces the water above it and creates a huge wave.

74
Q

How do tsunamis form?

A

They are caused by earthquakes at sea. The energy from an earthquake vertically jolts the seabed by several metres displacing hundreds of cubic kilometres of water. Large waves begin moving through the ocean, away from the earthquakes epicentre. In deep waer, the tsunami moves at great speeds. When it reaches shallow water near the coastal areaas, the tsunami slows but increases in height.

75
Q

What is the only warning system of a tsunami?

A

When the waterline suddenly retreats, exposing hundreds of metres of beach and seabed.

Geography (9 decks)

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