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A Level Physical Geography > Hazards: Tectonics/Volcanoes > Flashcards

Hazards: Tectonics/Volcanoes Flashcards

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1
Q

Name the layers of the earth

A

Crust
Mantle - lithosphere, asthenosphere
Outer core
Inner core

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2
Q

What elements make up the crust?

A 
Very light elements...
Silicon
Oxygen
Sodium
Aluminium
Potassium
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3
Q

Name the two types of crust

A

Continental

Oceanic

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4
Q

How thick is the continental crust?

A

30-70km thick

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5
Q

What is the continental crust made up of?

A

Granite

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6
Q

How thick is the oceanic crust?

A

6-10km thick

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7
Q

What is the oceanic crust made up of?

A

Basalt

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8
Q

Is continental or oceanic crust denser?

A

Oceanic

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9
Q

What is the mantle made up of?

A

Molten / semi molten rocks

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10
Q

What elements make up the mantle?

A

Light elements…
Silicon
Oxygen

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11
Q

What is the core made up of?

A

Dense iron / nickel alloys

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12
Q

Is the inner core solid or liquid?

A

Solid

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13
Q

Is the outer core solid or liquid?

A

Liquid

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14
Q

What temperature is the inner core?

A

> 5000°C

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15
Q

Where does the high temperatures in the core come from?

A

Primordial heat from the earth’s formation.

Radiogenic heat from radioactive decay of isotopes.

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16
Q

What consistency is the asthenosphere?

A

Semi molten

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17
Q

Where is the asthenosphere found?

A

Upper mantle - where convection is thought to occur

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18
Q

What is the lithosphere?

A

The solid layers of the earth

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19
Q

Where is the lithosphere found?

A

Crust and upper mantle

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20
Q

How thick is the lithosphere?

A

80-90km thick

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21
Q

How thick is the outer core?

A

2,200km

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22
Q

How thick is the inner core?

A

1,200km

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23
Q

Who developed plate tectonic theory? When?

A

Alfred Wegener, 1912

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24
Q

What was Alfred Wegener’s theory?

A

That a single continent existed 300million years ago - Pangea.
It area split into two continents - Laurasia (N), Gondwanaland (S).
Due to continental drift.

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25
Q

Give the geological evidence for Wegener’s theory of continental drift

A
  • Appeared that S America and W Africa would fit together.
  • Late Carboniferous glaciation (290million years ago) deposits found in S America, Antarctica and India.
  • Striations on rocks in Brazil and W Africa which point to similar situation.
  • Similar rock sequencing in N Scotland and E Canada.
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26
Q

Give the biological evidence for Wegener’s theory of continental drift

A
  • Similar fossil brachiopods found in Indian limestone and Australia.
  • Fossil remains of the Mesosaurus reptile are found in S America and S Africa.
  • Fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica.
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27
Q

What couldn’t Wegener’s theory explain?

A

He couldn’t explain how the continents could move, so his ideas gained little ground

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28
Q

When was more evidence revealed to suggest that Wegener could have been correct?

A

1940s

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29
Q

What evidence discovered in the 1940s supported Wegener’s theory?

A

Mid Atlantic Ridge and ridge in Pacific Ocean were discovered.
The surrounding ocean crust was examined -> sea floor spreading.

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30
Q

Give the evidence for sea floor spreading

A

Iron particles in erupted lava are aligned with the earth’s magnetic field.
The earth’s polarity reverses every 400,000 years approx -> series of magnetic stripes with rocks aligned alternately.
The crust gets older the further away from the ridge it is = suggests the oceanic crust is slowly spreading away from this boundary.

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31
Q

Name all the Earth’s tectonic plates

A 
Pacific Plate
North American Plate
Nazca Plate
South American Plate
African Plate
Eurasian Plate
Indo-Australian Plate
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32
Q

Which direction do plates move at a constructive boundary?

A

Plates move apart

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33
Q

What landforms/events are likely to occur at a constructive boundary?

A

Volcano - magma wells up to fill the gap and eventually a new crust is formed

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34
Q

Give a named example of a constructive boundary

A

Mid-Atlantic Ridge

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35
Q

Which direction do plates move at a destructive boundary?

A

Oceanic and continental plate move together.

Oceanic plate is denser so it subducts.

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36
Q

What landforms/events are likely to occur at a destructive boundary?

A

Volcano - friction causes oceanic plate to melt, magma rises through cracks and erupts.
Earthquakes - due to friction.

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37
Q

Give a named example of a destructive boundary

A

Nazca Plate is forced under South American Plate

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38
Q

Which direction do plates move at a collision boundary?

A

Two continental plates move together.

Neither is forced underneath the other so both are forced upwards.

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39
Q

What landforms/events are likely to occur at a collision boundary?

A

Fold mountains

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40
Q

Give named examples of a collision boundary

A

Himalayas
Rockies
Andes
Alps

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41
Q

Which direction do plates move at a conservative boundary?

A

Two plates slide past each other in opposite directions / same direction at different speeds.

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42
Q

What landforms/events are likely to occur at a conservative boundary?

A

Earthquakes - due to build up of friction leading to sudden movements.

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43
Q

Give a named example of a conservative boundary

A

San Andreas fault, California

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44
Q

Give an example of an oceanic ridge

A

Mid-Atlantic Ridge

45
Q

Where do oceanic ridges form?

A

Constructive boundaries - magma rises

46
Q

What landforms often occur along oceanic ridges?

A

Volcanoes, submarine volcanoes that may also rise above sea level.
Eg Surtsey, south of Iceland.

47
Q

Give an example of a rift valley

A

East African Rift System

48
Q

Where do rift valleys form?

A

Constructive boundaries - an area of linear shaped lowland is left between several highlands or mountain ranges when plates move apart.

49
Q

Do rift valleys form on land or in oceans?

A

Can be found on land or in oceans due to sea floor spreading.

50
Q

Give an example of a deep sea trench

A

Mariana Trench, west Pacific ocean

51
Q

Where do deep sea/oceanic trenches form?

A

Destructive boundaries - where oceanic plate subducts.

52
Q

At what depths are deep sea/oceanic trenches found?

A

7,300m - 11,000+m deep

53
Q

Give an example of island arcs

A

Marianas Islands and Guam

54
Q

What are island arcs?

A

Chains of volcanic islands that form parallel to oceanic trenches

55
Q

Where do island arcs form?

A

Destructive boundaries - parallel to deep sea/oceanic trenches

56
Q

Why do island arcs form?

A

When a plate subducts it melts due to friction/heat from the mantle -> magma is forced up through the overriding plate, forming a volcano.
When this occurs along an oceanic trench it forms a chain of volcanoes.

57
Q

Give examples of young fold mountains

A

Rockies, Himalayas

58
Q

Where do fold mountains form?

A

Collision boundaries - usually continental crusts

59
Q

Define young fold mountain

A

Mountains formed 10-25million years ago

60
Q

Define old fold mountain

A

Mountains that are >200million years old

61
Q

Give examples of volcanoes

A 
Calbuco, Chile (destructive boundary)
Hawaiian Islands (hotspot chain)
62
Q

Where do volcanoes form?

A

Constructive boundaries
Destructive boundaries
Hot spots

63
Q

What is the generally accepted view on what causes plate movement?

A

That convection currents cause plate movement

64
Q

Name the forces generated at plate boundaries that are thought to contribute to plate movement

A

Ridge push

Slab pull

65
Q

What is ridge push?

A

Oceanic plates experience a force that acts away from the ridge - the result of gravity acting down the slope of the ridge.

66
Q

What is slab pull?

A

Downward gravitational force that pulls the whole oceanic plate down - the result of the negative buoyancy of the plate.

67
Q

Why is there thought to be some frictional resistance to ridge push?

A

Shallow earthquakes occur due to the repeated tearing apart of the newly formed crust - suggests frictional resistance.

68
Q

Does the slab pull force lead to earthquakes?

A

Yes - due to friction created by pushing of the subducting plate against the overriding plate.

69
Q

Why does the importance of driving/retarding forces vary from plate to plate?

A

Each plate moves at its own rate

70
Q

How do hot spots form?

A

Radioactive decay within the Earth’s core generates very hot temperatures.
If the decay is concentrated, hotspots will form.

71
Q

How do hot spots create volcanic activity?

A

Hot spots heat the lower mantle, creating localised thermal currents where magma plumes rise vertically.
The plumes can burn/melt through the lithosphere to create volcanic activity on the surface.

72
Q

How do hot spots create a volcano chain?

A

The overlying plate moves over the stationary hot spot, resulting in a chain of active / extinct volcanoes in its path.

73
Q

Give an example of a hot spot chain of volcanoes

A

Hawaiian Islands, Pacific Plate

74
Q

Define hot spot

A

An area in the upper mantle where hot magma from the lower mantle upwells and melts through the crust.

75
Q

How many islands are there in the Hawaiian chain?

A

8

76
Q

Name the oldest Hawaiian island

A

Kauai - 5.5million years old

77
Q

Name the youngest Hawaiian island

A

Hawaii - 0.7million years old

78
Q

Give evidence for the Hawaiian islands being a result of hot spot volcanism

A

The islands get progressively older towards the northwest of the chain, with more being seamounts in this area.

79
Q

Define seamount

A

A large underwater mountain of at least 1000m height above the sea floor.
Usually form when volcanoes age and sink.

80
Q

Who came up with hot spot theory?

A

John Tuzo Wilson

81
Q

What did J. Tuzo Wilson argue?

A

That volcanic regions like Hawaii could only exist if there was a localised source of heat beneath them:
Hot spots = thermal plumes.

82
Q

Name the primary impacts of a volcanic eruption

A

Tephra
Pyroclastic flow
Lava flow
Volcanic gases

83
Q

Define tephra

A

Solid material of varying grain size ranging from volcanic bombs to ash, all ejected into the atmosphere.

84
Q

Define pyroclastic flow

A

Very hot, gas charged, high velocity flows made up of gas and tephra.

85
Q

Give the speed and temperature of pyroclastic flow

A

800*C

700km/h

86
Q

Give an example of an eruption that had an extreme impact by pyroclastic flow

A

Mt Vesuvius, Pompeii

87
Q

Define lava flow

A

Stream of molten rock that pours from an erupting vent

88
Q

Name the volcanic gases

A 
Carbon dioxide
Carbon monoxide
Hydrogen sulphide
Sulfur dioxide
Chlorine
89
Q

Give an example of an eruption that had an extreme impact by volcanic gases

A

Nyos, Cameroon, 1986

CO2 emissions killed 1700 people.

90
Q

Name the secondary impacts of volcanic eruptions

A 
Lahars
Flooding
Volcanic landslides
Tsunamis
Acid rain
Climatic change
91
Q

Define lahars

A

Combination of melted snow/ice and ash -> mud flows that move down the course of river valleys at high speeds.

92
Q

Give an example of an eruption that had an extreme impact by lahars

A

Nevado del Ruiz, Colombia, 1985.

3/4 of the town of Armero were killed.

93
Q

How can flooding result from an eruption?

A

When the eruption melts glaciers/ice caps.

94
Q

Give an example of an eruption that caused extreme flooding

A

Grimsvotn, Iceland, 1996

95
Q

Define volcanic landslide

A

Large masses of wet/dry rock and soil that fall, slide or flow very rapidly due to gravity.

96
Q

Define tsunamis as a result of volcanoes

A

Sea waves generated by violent volcanic eruptions

97
Q

Give an example of an eruption that led to a tsunami

A

Krakatoa, Indonesia, 1883.

Killed 36,000

98
Q

Define acid rain

A

When gases eg sulphur combine with atmospheric moisture.

99
Q

How can volcanic eruptions lead to climatic change?

A

The ejection of huge amounts of volcanic debris into the atmosphere can block the sun and reduce global temperatures.

100
Q

Give an example of an eruption that led to climatic change

A

Mt Pinatubo, Phillipines, 1991

101
Q

By what means can people manage volcanic hazards?

A

Prediction

Mitigation - preparation, prevention, adaptation

102
Q

Is it easy/difficult to predict when a volcano will erupt?

A

Difficult

103
Q

How can the effects of volcanoes be managed by prediction?

A

Monitoring of ground deformation (swelling).
Changes in groundwater levels / chemical composition of gwater.
Changes in gas emissions -> higher sulphur = closer eruption.
Monitoring seismic activity using seismometers.
Monitoring temperature change using thermal imaging/ satellite cameras.

104
Q

Give an example of when prediction of a volcanic hazard was effective

A

Popocatepetl, Mexico, 2000.

Use of seismology saved 30,000 people.

105
Q

Name the means of mitigation of a volcanic hazard

A

Preparation
Prevention
Adaptation

106
Q

How can the effects of volcanoes be managed by mitigation: preparation ?

A 
Exclusion zones around the volcano.
Evacuation.
Emergency supplies of basic provisions.
Having funds available to deal with aftermath.
Good communication system -> warning.
Emergency shelters.
Hazard maps showing predicted pathway of eruption.
Educating residents of what to do.
107
Q

How can the effects of volcanoes be managed by mitigation: prevention ?

A

Prepared with evacuation routes.
Development of a warning system that detects seismology etc.
Building structures that are able to withstand eruptions.
Lava channels to redirect flows.
Building infrastructure away from danger zones.

108
Q

How can the effects of volcanoes be managed by mitigation: adaptation ?

A

Developing new monitoring systems.
Amendment to eruption plans based on past experience.
Modification to prevention methods based on past experience.
Residents may choose to relocate.

A Level Physical Geography (10 decks)

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