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Geography > Tectonics > Flashcards

Tectonics Flashcards

1
Q

What is the global distribution of earthquakes?

A

Most earthquake zones are found at, or close to, tectonic plate boundaries, often in clusters. 70% of all earthquakes are found in the ‘Ring of Fire’ in the Pacific Ocean.

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2
Q

What is the oceanic fracture zone (OFZ)?

A

A belt if activity through the oceans along the mid-ridges, coming ashore in Africa, the Red Sea, the Dead Sea rift and California

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3
Q

What is the continental fracture zone (CFZ)?

A

a belt of activity following the mountain ranges from Spain via the Alps, to the Middle East, the Himalayas to the East Indies and then circumscribing the Pacific.

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4
Q

What is the cause of earthquakes?

A

Earthquakes are a sudden release of stored energy. As two plates move past each other they inevitably ‘stick’. This allows strain to build up over time and the plates are placed under increasing stress. Earthquakes are generated because of the sudden release of the stress. A pulse of energy radiates out in all directions from the earthquake focus. In some cases the earthquake motion displaces the surface, so a fault scarp can be seen.

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5
Q

What is the global distribution of tsunamis?

A

Around 90% of all events occur within the Pacific Basin, associated with activity at the plate margins. Most are generated at subduction zones (convergent boundaries).

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6
Q

What are the causes of tsunamis?

A

Tsunamis are generated when a sub-marine earthquake displaces the sea bed vertically as a result of movement along a fault line at a subduction zone. The violent motion displaces a large volume of water in the ocean water column, which then moves outwards in all directions from the point of displacement.

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7
Q

What is subduction?

A

the process of one plate sinking beneath another at a convergent plate boundary.

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8
Q

What is Gravitational Sliding?

A

Constructive margins have elevated altitudes because of the rising heat between them, which creates a ‘slope’ down which oceanic plates slide. This occurs at destructive plate margins

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9
Q

What is Slab Pull?

A

newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools. This causes it to sink into the mantle under its own weight- pulling the rest of the plate further down with it

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10
Q

What is Mantle Convection?

A

heat produced by the decay of radioactive elements in the Earth’s core heats the lower mantle- creating convection currents

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11
Q

What is Seafloor Spreading?

A

in the middle of the oceans are huge mid-ocean ridges, or underwater mountain ranges. These are formed when hot magma is forced up from the asthenosphere and hardens- forming new oceanic crust. This new crust pushes the tectonic plates apart in a process called seafloor spreading

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12
Q

What are the 3 types of boundary?

A

CONVERGENT
DIVERGENT
CONSERVATIVE

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13
Q

What is a convergent plate boundary?

A

where two plates collide, known as destructive margins

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14
Q

What is a divergent plate boundary?

A

where two plates move apart, known as constructive margins

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15
Q

What is a conservative plate boundary?

A

where two plates slide past each other, also known as transform margins

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16
Q

Destructive plate margins- what happens when an oceanic plate meets a continental plate?

A

oceanic plate is denser than continental plate, so, when the plates collide, the oceanic plate slides beneath the continental plate into the mantle and melts

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17
Q

What is the Benioff Zone?

A

The friction created between the colliding plates causes intermediate and deep earthquakes in an area called the Benioff Zone

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18
Q

What do destructive plate margins (when oceanic meets continental) form?

A

Deep ocean trenches mark the place where the oceanic plate starts to sink beneath the continental plate
The subduction also leads to the formation of fold mountains

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19
Q

Destructive plate margins- what happens when an oceanic plate meets an oceanic plate?

A

when oceanic plates collide, one plate (the denser or faster) is subducted beneath the other. The subducted plate then melts- creating magma, which rises up from the Benioff Zone to form underwater volcanoes.

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20
Q

Destructive plate margins- what happens when a continental plate meets a continental plate?

A

when two continental plates meet, a collision margin occurs- they collide and sediments between them are crumpled and forced up to form high fold mountains, like the Himalayas. However, inevitably there are can be some subduction caused when the compressed sediments result in plate subduction beneath them

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21
Q

Conservative plate margins- what are mid ocean ridges?

A

mid ocean ridges of underwater mountains extend for over 60,000 km across the world’s ocean floor- regular breaks called transform faults cut across these ridges.
Regular volcanic eruptions also create submarine volcanoes along these mid-ocean ridges

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22
Q

Conservative plate margins- what are rift valleys?

A

when plates move apart on continents, the crust stretches and breaks into sets of parallel cracks (faults). The land between these faults then collapses, forming steep-sided valleys called rift valleys

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23
Q

What are the 3 types of seismic waves?

A

primary waves
secondary waves
love waves

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24
Q

How are earthquakes measured

A

earthquake magnitude- Moment Magnitude Scale (MMS)
earthquake intensity- Modified Mercalli Intensity Scale

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25
Q

What are the primary effects of an earthquake?

A
  • ground shaking
  • crustal fracturing
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26
Q

What are the secondary effects of an earthquake?

A
  • liquefaction- violent shaking causes surface rocks to lose strength and become more liquid than solid- buildings and roads tilt or sink
  • landslides and avalanches- ground shaking places stress on slopes
  • tsunamis- underwater earthquakes generate tsunamis
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27
Q

What are volcanoes?

A

openings int he Earth’s crust through which lava, gas and ashes erupt

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28
Q

How do volcanoes form?

A

As tectonic plates move, pressure builds and hot magma and gases push up from the mantle to the Earth’s crust- and erupt
when the magma reaches the Earth’s surface its called lava
when lava cools, it forms rock

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29
Q

What are the primary hazards of volcanic eruptions?

A

lava flows
pyroclastic flows
tephra and ash falls
gas eruptions

30
Q

what are lava flows?

A

streams of lava that have erupted from a volcano onto the Earth’s surface. Not particular threat to humans but destroy

31
Q

what are pyroclastic flows?

A

mixtures of dense rock, lava, ash and gases ejected from a volcano, which move very quickly across Earth’s surface. Hot and destroy- travel 100km/h

32
Q

what are tephra and ash falls?

A

TEPHRA- pieces of rock and ash that blast into the air during volcanic eruptions. Smaller pieces travel far whereas larger pieces tend to fall near to the volcano, where they cause injury or death
ASH FALLS- ash lands and covers everything- poor visibility and slippery roads- roofs collapse and engines clog

33
Q

what are gas eruptions?

A

magma contains dissolved gases that are released into the atmosphere during a volcanic eruption- can travel

34
Q

What are the secondary hazards of volcanic eruptions ?

A

Lahars
Jokulhlaup
Hot Spots

35
Q

what are lahars?

A

masses of rock, mud and water that travel quickly down the sides of a volcano. They are caused when an eruption quickly melts snow and ice or heavy rainfall during or after an eruption erodes loose rock and soil- surges downslope

36
Q

what is a jokulhlaup?

A

heat of a volcanic eruption can melt the snow and ice in a glacier- causing heavy and sudden floods called jokulhlaups. Can be dangerous as they suddenly release large amounts of water, rock, gravel ad ice that can catch people unaware and flood and damage structures

37
Q

what are hot spots?

A

volcanoes can also form in the middle of a plate, where plumes of hot magma rise upwards and erupt onto the sea floor (at what is called a hot spot).

38
Q

What are tsunamis and how are they generated?

A

can be generated by landslides or even the eruptions of volcanic islands, but most are generated by sub-marine earthquakes
generated when a sun-marine

39
Q

how do sub-marine earthquakes form tsunamis?

A

generated when a sun-marine earthquake displaces the sea bed vertically as a result of movement along a fault line at a subduction zone. The violent motion displaces a large volume of water in the ocean water column, which then moves outwards from a point of displacement.

40
Q

What is the PAR model?

A

suggests that the socio- economic context of a hazard is important, in poorly-governed (root causes) places with rapid change and low capacity (dynamic pressures) and low coping capacity (unsafe conditions), disasters are likely

41
Q

How does the level of development affect the impact of tectonic hazards?

A

population growth, urbanisation, environmental degradation, very young or old population, inadequate infrastructure…
warning and emergency response systems, economic wealth, government disaster-assisant programmes, insurance, community initiatives, scientific understanding..

42
Q

How does the level of governance impact vulnerability?

A

meeting basic needs, planning, environmental management, preparedness, corruption, openness

43
Q

What geographical factors impact the vulnerability?

A

population density- highly populated areas are hard to evacuate
degree of urbanisation
isolation and accessibility- can slow the rescue relief effort

44
Q

what are hydro-met hazards and what is their trend?

A

floods, storms, cyclones and drought appear to have become more common overtime, perhaps because of global warming and human environmental management issues such as deforestation

45
Q

what is the trend of tectonic disasters?

A

the events have not increased or decreased overtime- the number of events is broadly the same

46
Q

what are the trends in death toll ?

A
  • deaths have fallen overtime because better response management, preparation and prediction-
    120,000 in 1975, 90,000 in 1980, 70,000 in 2000, 20,000 in 2015
47
Q

what is the trend in number of reported disasters?

A

the number of reported disasters increased then stabilised as improvements in data coverage and accuracy of data bases increased

48
Q

what is the trend in umber of people affected by disasters?

A

the number of people affected by disasters continues to rise as populations grow and more live in risky locations

49
Q

What are megadisasters?

A

they are high magnitude, high impact, infrequent disasters that affect multiple countries (directly or indirectly), so their impacts are regional or even global

50
Q

What are multiple hazard zones?

A

they are places where two or more natural hazards occur, and in some cases interact to produce complex diasasters

51
Q

What does prediction mean?

A

Prediction means knowing when and where a natural hazard will strike on a spatial and temporal scale that can be acted on meaningfully in terms of evacuation

52
Q

What is forecasting?

A

Forecasting is much less precise than prediction and provides a percentage change of a hazard occurring

53
Q

can earthquakes be predicted and how?

A
  • they cannot be predicted
  • only areas at high risk can be identified (risk forecasting) plus areas that are likely to suffer severe ground shaking and liquefaction- used for land zoning purposes
  • ‘seismic gaps’- areas that have not experienced an earthquake for some time and are overdue- can point to areas at high risk
54
Q

can volcanic eruptions be predicted and how?

A
  • can be predicted
  • sophisticated monitoring equipment on volcanoes can measure changes s magma chambers fill and eruption nears
  • tiltmeters and strain meters record volcanoes ‘bulging’ as magma rises and seisometers record minor earthquakes indicating magma movement
  • gas spectrometers analyse gas emissions which can point to increased eruption likelihood
55
Q

can tsunamis be predicted and how?

A
  • can be partly predicted
  • an earthquake-induced tsunami cannot be predicted
  • However, seisometers can tell an earthquake has occurred and locate it, then ocean monitoring equipment can detect tsunami int he open sea
56
Q

What is the hazard management cycle?

A

it illustrates the different stages of managing hazards in an attempt to reduce the scale of a disaster. It is a cycle, with one disaster event informing preparation for the next

57
Q

What are the different stages of the hazard management cycle?

A
  • response
  • recovery
  • mitigation
  • preparedness
  • recovery stage
58
Q

What is park’s model?

A

the importance of recovery can be seen on park’s model: the disaster-response curve.
Provides a simple visual illustration of the impact of a disaster, and can be used to compare different events

59
Q

what are the three ways to modify the impacts of a disaster?

A
  • modify the event
  • modify the vulnerability
    -modify the loss
60
Q

What is land use zoning and what are the adv/disadvantages of using it ?

A

Land use zoning prevents people from building:
- on low-lying coasts (at risk from tsunami and flooding)
- close to volcanoes
- on areas of high ground shaking and liquefaction risk
advantages: low cost, removes people from high risk areas
disadvantages: prevents economic development on some high-value land, requires strict, enforced planning rules

61
Q

What are aseismic buildings?

A

Buildings that are strong enough to resist (most) earthquakes and prevent damage. They may include:
- cross-bracing (reinforced structures, since one diagonal brace may be in tension whilst the other is slack)
- counter weights
- deep foundations
- hollow concrete bricks designed to cause minimal damage
- reinforced cement concrete roof
- reinforced steel corner pillars to provide strength and flexibility

62
Q

What are tsunami defences and what are the adv/disadvantages of using them?

A

Tsunami sea walls and breakwaters, which prevent waves travelling inland
advantages: Dramatically reduces damage
Provides a sense of security
disadvantages: Can be overtopped
Very high cost
Ugly and restrict use/development at the coast

63
Q

What us lava diversion and what are the adv/disadvantages of using it?

A

Channels, barriers and water cooling used to divert and/or slow lava.
Advantages
- Diverts lava out of harm’s way
- Relatively low cost
Disadvantages
- Only works for low VEI basaltic lava
- The majority of ‘killer’ volcanoes are not of this type

64
Q

What is meant by modifying vulnerability?

A

increasing the resilience of a community to increase their capacity to cope. In many cases, prediction, warning, and evacuation are used to move people out of harm’s way.

65
Q

what is high-tech scientific monitoring? (for prediction)

A

This is used to modify the behaviour of volcanoes and predict eruptions.
Advantages:
- In most cases, predicting an eruption is possible
- Warnings and evacuation save lives
Disadvantages
- Costly, so not all developing world volcanoes are monitored
- May suffer from ‘cry wolf syndrome’ if predictions are not accurate
- This is where predictions (and evacuation) are wrong, so people are less lively to believe the next one.
- Does not prevent property damage

66
Q

what are the advantages of using community preparedness and education?

A

Examples of this are: preparation days, education in schools and earthquake kits. These are boxes of essential household supplies (water, food, battery powered radio, blankets) kept in a safe place at home to be used in the days following an earthquake.

Advantages
- Low cost, often implemented by NGOs
- Can save lives through small actions
Disadvantages:
- Does not prevent property damage
- Harder to implement in isolated rural areas

67
Q

What are the adv/disadvantages of using adaptation strategies?

A

Advantages
- Would save both lives and property
Disadvantages
- High population densities prevent it
- Disrupts people’s traditional homes and traditions

68
Q

What is meant by modifying loss?

A

Loss modification could be described as ‘picking up the pieces’ after a disaster has occurred. Losses should be small if event and vulnerability modification have been used, however loss modification is often the main management strategy in developing countries.

69
Q

What are the adv/dis of using short term emergency aid?

A

Advantages
- Reduces death toll by saving lives and keeping people alive until longer-term help arrives
Disadvantages
- High cost
- Difficult to distribute in isolated areas
- Emergency services are limited and poorly equipped in developing

70
Q

What are the adv/dis of long term aid?

A

Advantages
- Reconstruction can ‘build in’ resilience through land-use planning and better construction methods
Disadvantages
- Very high costs
- Needs are quickly forgotten by the media after the initial disaster

71
Q

What are the adv/dis of insurance?

A

Advantages
- Allows people to recover economically by paying for reconstruction
Disadvantages
- Does not save lives
- Few people in the developed world have insurance.

Geography (11 decks)

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