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Undeleted > Chapter 1: Locations-risk-tectonic hazards > Flashcards

Chapter 1: Locations-risk-tectonic hazards Flashcards

1
Q

Where are earthquakes found?

A

Earthquakes are found along plate boundaries.

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2
Q

What boundaries are associated with the most powerful earthquakes?

A

Convergent and Conservative plate boundaries

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3
Q

What three things are in the tectonic activity pattern?

A
  • Ocean fracture zone
  • Continential fracture zone
  • Scattered earthquakes in continential interiors.
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4
Q

What is the Ocean fracture zone?

A

Belt of earthquake activity through oceans along mid ocean ridges.

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5
Q

What is the Continential fracture zone?

A

Its a belt of earthquake activity following the mountain ranges from Spain to the Middle East.

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6
Q

What are scattered earthquakes in continential interiors?

Give an example.

A

The reactivasion of earhtquakes in weaknesses on old fault lines

Church Stretton fault in Shropshire.

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7
Q

What makes Earthquakes dangerous?

A

They are primary hazards (grund movement) that can cause secondary hazards e.g. landslides.

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8
Q

Define primary hazards.

A

Hazards that cause the ground to move.

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9
Q

Define Secondary hazards.

Give an example

A

Hazards caused by primary hazards,

e.g. Landslides, Tsunamis

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10
Q

Define: Volcano

A

A landform that develops around a weakness in the earth’s crust from which molten magma, volcanic rock and gases are ejected or extruded.

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11
Q

How is the violence of a volcanic eruption determined?

A

Amount of dissolved gases in magma and how easily the gases can escape.

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12
Q

What else can you call Constructive plate boundaries?

A

Divergent plate boundaries.

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13
Q

True or false: Constructive plate boundaries are low magnitude.

A

True

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14
Q

Do you find shallow focus events at constructive plate boundaries?

A

Yes.

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15
Q

In what way do plates move at constructive plate boundaries?

A

Plates move apart. < I >

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16
Q

In what way do plates move at convergent plate boundaries?

A

Plates move together. > I <

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17
Q

How do convergent plate boundaries cause frequent earthquakes and volcanoes?

A

They deform collision locations causing frequent earthquakes and volcanoes.

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18
Q

Do you find shallow focus earthquakes at conservative plate boundaries?

A

yes

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19
Q

How strong are magnitudes usually from conservative plate boundaries?

A

Very strong.

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20
Q

In which way do plates move at conservative plate boundaries.

A

Both directions against each other.

  • >

< -

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21
Q

What are the characteristics of earthquakes caused by constructive plate boundaries?

A

Earthquakes are frequent, small and a low hazard risk.

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22
Q

What do constructive plate boundaries create?

A

Creates new oceanic crust that is thinner and denser than continential crust.

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23
Q

What do conservative plate boundaries create?

A

Create friction which risks snagging.

E.g. Pacific plate and North American plate at San Andreas.

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24
Q

Convergent plate boundaries are the most damaging. Explain why.

A

Oceanic plate slides under continential plate as its denser, creating a subduction zone. Friction causes snags which are eventually overcome. This sudden jolt creates Tsunamis

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25
Q

What determins volcanic activity and distrabution.

A

Plate tectonics.

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26
Q

How do volcanoes form on convergent plate margins.

A

Volcanoes form at convergent plate margins when the mantle burns through the subducted oceanic plate picking up minerals as it goes. It then burns through the continential plate eventually forming a volcano.

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27
Q

Constructive boundaries create which volcanoes?

A

Rift volcanoes.

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28
Q

What are characteristics of Rift volcanoes.

A

Weaker eruption, very effusive as magma burns through thin layer of oceanic plate.

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29
Q

What are Hotspot volcanoes? And what are their characteristics?

A
  • Found in the middle of tectonic plates
  • Fed by underlying mantle plumes
  • Very hot compared to surrounding mantle
  • E.g. Hawaiin volcanoes within Pacific plate.
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30
Q

True of False: Magma picks up minerals under Hotspot valcanoes by burning through the plate during hot thermal plumes.

A

True

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31
Q

What are the two types of crust?

A
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32
Q

True or False: Oceanic crust is thicker than Continential crust.

A

False

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33
Q

What does each plate underline?

A

Oceanic crust underlines Ocean basins.

Continential crust underlines the continents.

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34
Q

What is each plate composed of?

A

Oceanic crust = Basalt primarily.

Continential crust = Granite primarily.

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35
Q

Whats the difference between rocks in the upper and lower mantle?

A

Upper mantle rocks are cool and brittle so cause earthquakes.

Lower mantle rocks are soft and weak so flow with forces.

36
Q

What causes plates to move?

A

Heat from the earth’s core rises in the mantle to cause convection currents that move tectonic plates.

37
Q

What is radioactive decay?

A

Heat from the earth’s core

38
Q

What can plate movements be translated into?

A

Plate movements can be translated into Hazard risks.

39
Q

How do we date the age of new tectonic crust?

A

Reconstructing paleomagnetic reversals

40
Q

What is the Benioff zone?

A

An area of seismicity corresponding with the oceanic slab in a subduction zone. It is the site of deep focused earthquakes and so theoretically it is good at earthquake magnitude as it determines the position and depth of the hypocentre.

41
Q

How do people work out the distribution of earthquakes?

A

Plot plate boundaries that have caused primary hazards in the past.

42
Q

What is the process of an earthquake?

A
  1. At faults in earth’s crust there is a gradual build up of tectonic strain.
  2. When the pressure exceeds the strength of the fault the rock fractures.
  3. Produces a sudden release of energy creatign seismic waves.
  4. Brittle ground rebounds either side of fracture which is ground shaking.
43
Q

Define: Hypocentre

A

The point of rupture underground.

44
Q

What does a Seismometer measure?

A

Measures the horizontal and vertical movements of the ground.

45
Q

What are the three types of seismic waves earthquakes produce?

A
  • P waves, vibrations caused by compression
  • S waves, vibrate at right angles to direction of travel
  • L waves, surface waves on a horizontal plain
46
Q

What does earthquake severity depend on?

A

The strength of it’s seismic waves.

47
Q

What is Soil liquefication?

A

A side effect of earthquakes,

Water saturated material loses normal strength and behaves like a liquid due to strong shaking.

48
Q

What can soil liquefacation cause?

A

Buildings to collapse and sloping ground.

49
Q

Soil liquefacation causes sliding as it reduces friction. What is this called?

A

Lateral spreading.

50
Q

What can lateral spreading from soil liquefacation cause?

A

Fissures in the ground.

51
Q

What are some consequences of lateral spreading?

A

Damage to roads, bridges, and communications.

52
Q

What is a short term and long term impact of lateral spreading?

A

Short term- delivery of aid.

Long term- rebuilding costs

53
Q

What causes landslides?

A

When slopes weaken and fail.

54
Q

What are landslides impacts of?

Where do they occur?

A

secondary impacts of destructive earthquakes.

Mostly occur in mountain areas.

55
Q

In what scale of earthquakes do landslides rarely occur?

A

In 1-4 magnitude earthquakes do landslides rarely occur.

56
Q

What are landslides particularly hazardous to?

A

People with property.

57
Q

Give an example of a place landslides often occur?

A

Nepal.

58
Q

Whats unusual about Tsunami’s wavelengths?

A

They are much longer than average.

59
Q

Where are Tsunamis the most dangerous and why?

A

Mostly dangerous at coastlines as they vary in height.

60
Q

What causes the series of waves in Tsunamis?

A

Seabed displacement.

61
Q

Why are Tsunamis dangerously unpredictable?

A

Time between the waves vary.

62
Q

From where are most Tsunamis generated? Example?

A

Subduction zones.

E.g. Japan-Taiwan island arc.

63
Q

What are the six factors that impact Tsunami damage?

A
  • Duration of event
  • Wave amplitude, Water collumn displacement and distance travelled.
  • Physical geography of coast, especially water depth and gradient of shoreline.
  • Degree of coastal ecosystem buffer, e.g. protection by mangroves.
  • Timing of event and quality of the warning systems.
  • Degree of coastal development and its proximity from the coast.
64
Q

When is a tsunami at its most dangerous?

A

When its influenced by both physical and human factors.

65
Q

What are the primary hazards caused by volcanoes?

And what do they all have in common?

A

Pyroclastic flows, Tephra, Lava flows and Volcanic gases.

They all have very long geographical reach.

66
Q

What is in pyroclastic flows?

A

Hot gas, volcanic debri, glass, pumice, crystals and ash.

67
Q

Why can pyroclastic flows flow upwards?

A

They are not dense.

68
Q

What makes pyroclastic flows incredibly dangerous?

A

They are extremerly fast and hot.

E.g. can reach 700 km/h and 1000°C

69
Q

What is volcanic tephra?

A

Rock fragments ejected into atmosphere by valconoes.

That can vary from bombs to fine dust.

70
Q

What negative impacts can volcanic tephra cause?

A

Can casue fires and buildings to collapse.

Dust can reduce visibility and effect air travel.

71
Q

When is lava at its most threatening and what are it’s propeties when it is?

A

Lava is the most threatening when it flows fast.

It flows fast from low viscocity, when it has little silicon dioxide.

72
Q

What determines lava’s viscocity?

A

How much silicon dioxide it contains.

73
Q

What eruptions are volcanic gases associated with?

A

Explosive ones.

74
Q

What does volcanic gas normally include?

A

Water vapour, Sulphur dioxide, hydrogen and Carbon monoxide.

75
Q

Why is Carbon monoxide from volcanic gas especially dangerous?

A

It can’t be detected as it is colourless and odorless.

76
Q

What are the two most significant secondary impacts of volcanic eruptions?

A

Volcanic mudflows (Lahars)

Catastrophic floods (Jökulhlaups)

77
Q

What are Lahars composed of?

A

Fine sand and silt.

78
Q

What mainly causes Lahars?

A

Heavy rainfall.

79
Q

What influences the degree of the Lahar hazard?

A
  • Steepness of slope
  • Volume of material and partical size
    *
80
Q

What are Jökulhlaups?

A

A type of glacial outburst flood.

81
Q

What are the main impacts of Jökulhlaups?

A

Can modify landscape via erosion and deposition.

Can cause a lot of property damage.

82
Q

What happens during a Jökulhlaup?

A

A large rapid discharge of water, ice, and debris come from a glacial source.

83
Q

Where do Jökulhlaups occur?

A

Anywhere where water accumulates in a subglacial lake beneath a glacier.

84
Q

What causes Jökulhlaups?

A

A failure in ice in glacier or Moraine dam.

85
Q

How many have died in volcanic eruptions in in the last 300 years?

A

Over 250,000 people.

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