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Eddie's Geography > 2.1 volcanos and earthquakes > Flashcards

2.1 volcanos and earthquakes Flashcards

1
Q

What ideas does the theory of plate tectonics encapsulate

A
  • Continents drift over the surface of the earth
  • Sea floor is removed and destroyed along continental margins
  • Sea floor is continuously regenerated at mid-ocean ridges
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2
Q

Label the structure of the earth

A
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3
Q

What is the crust

A

Relatively thin and rocky, broken up into plates

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4
Q

What is the mantle

A
  • Has the properties of a solid but can flow very slowly
  • It is plastic
  • Up to 3800*C
  • Makes up 82% of the earth’s volume
  • 2900 km from the earth’s surface
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5
Q

What is the outer core

A
  • Made up of iron and nickel
  • Liquid
  • 5100 miles from the earth’s surface
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6
Q

What is the inner core

A
  • Made up of solid iron and nickel
  • Up to 5500*C
  • 6400 kilometres from the earth’s surface
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7
Q

What is a continental plate

A
  • Crust that makes continents (dry land)
  • Made of granite
  • 1500 million years old
  • Between 25-100km thick
  • Less dense then oceanic crust
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8
Q

What is oceanic crust

A
  • Crust under oceans
  • Less than 200 million years old
  • Made up of basalt
  • 5-10 km thick
  • Denser than continental crust
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9
Q

What are the three reasons plates move

A
  • Convection currents
  • Slab pull
  • Ridge push
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10
Q

What is convection current

A
  • When plates are floating on extremely hot mantle, the intense heat in the earth’s core gives rise to convection currents that cause the plates to move
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11
Q

What is slab pull

A
  • Old oceanic plate, sinking into the mantle at destructive boundaries, pulls the rest of the plate down with it
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12
Q

What is ridge push

A
  • New material formed at constructive plate boundaries forces the plates away
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13
Q

What is a constructive plate boundary

A
  • Two plates move apart from each other causing sea floor spreading
  • New oceanic crust is formed, creating mid-ocean ridges
  • Volcanic activity is common
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14
Q

What is a convergant/ destructive plate boundary

A
  • When the oceanic crust sinks below the contintental crust due to its greater density
  • Deep sea trenches and island-arcs are formed
  • The continental crust is folded into fold mountains
  • Volcanic activity is common
    *
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15
Q

What is a convergant/ collision plate boundary

A
  • Two continental crusts collide
  • As neither can sink they are folded up into fold mountains
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16
Q

What is a conservative plate boundary

A
  • Two plates slip sideways past each other but neither land is destroyed nor created
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17
Q

What is an earthquake

A
  • A sudden movement in rock
  • Relatively near the earth’s surface along a zone of geological weakness called a fault
    *
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18
Q

Describe how earthquakes occur (elastic energy)

A
  • Most earthquakes occur where plates meet in subduction zones
  • Slow movement of plates deform crustal rocks and produces stored elastic energy
  • When the stored stress exceeds the strength of the fault it fractures
  • The sudden release of energy produces seismic waves
  • The fracture of the crust followed by the elastic rebound either side of the fault produces ground shaking
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19
Q

What is the focus of an earthquake

A
  • The orginal point of the earthquake where the two plates have moved relative to each other
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20
Q

What is the epicentre of an earthquake

A
  • The point on the earth’s surface directly above the focus
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21
Q

How is the energy recorded from an earthquake

A
  • From a seismometer
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22
Q

Why could a big earthquake occur

A
  • Large amount of movement at the fault
  • A rupture occuring over a long distance
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23
Q

What does the destruction of an earthquake depend on

A
  • Distance
  • Building quality
  • Duration of shaking
  • population density
  • local conditions
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24
Q
  • Why is ground shaking a primary hazard from earthquakes
  • What are the four types of wave
A
  • Due to seismic waves
  • Primary, secondary, Reighley and Love waves are the seismic wave types
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25
Q

Why is local conditions an earthquake hazard

A
  • Waves can be amplified by ridge crests as ground mtoions in soil are amplified in amplitude and duration
    *
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26
Q

How were earthquake hazards dealt with

A
  • Hazard resistant design - the implementation of construction sites, building materials, shock absorbers, building re-enforcement, building shape
27
Q

How can building materials decrease risk of earthquake

A
  • Replace stiff and weak building materials with felxible and string building materials improves building strength
    *
28
Q

How does building shape decrease the risk of earthquake hazards

A
  • Because tall slender buildings magnify shaking at the top whereas concical structure provides resistance to shaking
29
Q

How do construction sites affect earthquake hazards

A
  • Avoid building on soft soil, steep slopes and geological faults as it increases chance of building collapse
30
Q

How does building re-enforcement decrease the risk of earthquakes

A

Buildings can be strengthened by cross-baring, using external steel frames or particularily deep foundations

31
Q

How do shock absorbers decrease the risk of earthquakes

A
  • Isolates buildings from destructive horizontal ground shaking
32
Q

What protection methods are used against tsunamis

A
  1. Moving settlements
  2. Sea walls
  3. Break waters
  4. Coastal redevelopment
  5. Bioshields i.e. coastal tree plantations
33
Q

How can earthquakes be forecasted and warned about

A
  • Probablistic methods - examining historical records, works well with small earthquakes as there are lots of them to work with data-wise
  • Deterministic methods - Looking at seismic patterns, ground water levels and animal behaviour
    *
34
Q

What things within land use planning are sed to find the most affected areas in earthquakes

A
  • Fault location
  • Ground type
  • Slope angle
35
Q

Explain why number of deaths and injuries in earthquakes are more in LEDC’s than MEDC’s

A
  • Poor quality buildings - not using shockabosrbers and reinforcements for buildings
  • Not having evacuation procedures and education on earthquakes such as drills
  • Lack of medical care
  • Lack finance to rebuild and recover
  • Rescue teams poorly prepared so they must wait for international aid
36
Q

Describe the effects on people of a powerful earthquake

A
  1. Death/injury
  2. Destruction/ damage of buildings
  3. Damage to possessions/ roads/ railways
  4. Loss of electricity/ gas/ telephone lines
  5. Fires and contamination or loss of water
  6. economic collapse with loss of jobs
  7. Loss of government buildings
37
Q

What can be done to reduce the impacts of earthquakes on local people

A
  1. Building “earthquake proof” builds with deper and flexible foundations; shatter proof glass; and buildings in pyramid shapes
  2. Stronger flexible bridges
  3. Earthquake drills/ educate people what to do in an earthquake; leave areas of emptty land to use during an evacuation
  4. Hazard mapping, avoid building strategic buildings on plate boundaries
  5. Improve medical care and rescue teams/ medical staf on stand by
38
Q
A
39
Q

What are the three lifes of volcanoes?

A
  • Active - still erupting frequently
  • Dormant - not currently erupting but could do so in the future
  • Extinct - will never erupt again
40
Q
  • What are the features of a composite volcano?
  • Where are they found
A

A composite volcano has

  • Steep sides, symetrical shape, narrow base
  • Has layers of lava and ash
  • Has acidic lava - high silica content, viscous and flows a short distance
  • Rare, but explosive eruptions
  • They are found at destructive plate boundaries
41
Q
  • What are the features of a shield volcano?
  • Where are they found
A

A shield volcano has

  • Gentle sloping sides, a wide base
  • Basic lava - low silica content, has a fluid texture and flows a long distance
  • Frequent but gentle eruptions
  • Shield volcanos occur along constructive plate boundaries
42
Q

How do divergant plate boundaries occur

A
  1. Convection currents within the mantle occur due to heating from the outer core
  2. Plates move apart, creating a line of weakness
  3. Magma can reach the surface through this and an eruption occurs
43
Q

How do eruptions occur on convergant plate boundaries

A
  1. Convection currents occur within the mantle due to the heating of the outer core
  2. This forces the plates together where the oceanic plate is subducted
  3. The subducted plate is subject to intense friction and heating
  4. Progressively the plate melts producing magma under high pressure
  5. The magma gradually rises through the lines of weakness and fills a magma chamber
  6. When the pressure within the magma chamber is high enough, an eruption occurs
44
Q

What are the primary hazards caused by volcanos

A
  • Pyroclastic flows
  • Ash and tephra
  • Lava flows
  • Volcanic gases
45
Q

What are pyroclastic flows

A
  • When molten magma froths in the vent of the volcano and burst explosively to eject of mixture of hot gases and pyroclastic materials
  • These can flow down hillsides at 30-40km/h as they are denser than air
46
Q

What is ash/ tephra

A
  • This is comprised of all the fragmented material ejected by the volcano that subsequently falls to the ground
  • Heavy falls can blanket the landscape
  • Light falls contaminate farmland and create distruption and building damage in urban areas
47
Q

What are lava flows

A
  • Low viscosity streams of lava which can move down steep slopes at 15m/s
  • These can rapidly emerge from fissures
48
Q

What are volcanic gases

A
  • These are released by explosive eruptions and lava flows
  • The main, fatal gas released is CO2 as it is colourless and odourless
  • When falling on low lying areas it can cause dister as it displaces the less dense oxygen at ground level where humans inspire air
49
Q

What are the secondary hazards of volcanos

A
  • Lahars
  • Tsunamis
  • Landslides
    *
50
Q

What are lahars

A
  • Volcanic mudflows
  • They occur when high density rainfall/ ice/ melting snow mix with ash/tephra and deposit on the side of a volcano
  • They can flow at speeds of 22m/s
51
Q

How can volcanos cause tsunamis

A
  • These can be caused by large amounts of debris into the sea or a caldera collapsing
52
Q

How are landslides caused by volanic eruptions

A
  • Progressive ulift of one side of a volcano ahead of an eruption creates bulges of unstable land
  • Landslides can be triggered by small earthquakes
53
Q

What are methods of volcano hazard protection

A
  • Explosives
  • Artificial barriers
  • Water sprays
  • Barriers and sediment traps
  • Artificial degassing
54
Q

How are explosives used as hazard protection against volcanos

A
  • Used to bomb the lava high on a volcano in order to spread the flow
  • This may halt the advancing lava front by depriving it of supply
55
Q

How are artificial barriers used to prevent hazards caused by volcanos

A
  • Used to divert lava flows away from valuable property
  • Barriers are constructed from massive rocks or other resistant material with a broad base and gentle slopes
  • Works best from thin and fluid lava flows
56
Q

How are water sprays used to prevent hazards caused by volacanos

A
  • Used to solidify lava flows
  • *
57
Q

How are barriers and sediment traps used to prevent lava flow

A
  • Used to provide physical protection against lahars
  • Such storages are expensive and have a limited life span
  • They can only be located where lahar paths are well-defined and do not work for major destructive flows in deep valleys
    *
58
Q

How does artificial degassing prevent hazrads caused by volcanos

A
  • When high concentrations of CO2 enter the bottom of lakes via underground springs
  • If this CO2 is suddenly released in gas clouds, it could cause damage to aquatic life as they would die by asphyxiation
  • This threat therefore is minimised by the CO2 rich water to the lake surface where the gas can enter the atmosphere in safe amounts
59
Q

What opportunities are created by volcanos

A
  • Geothermal energy - generated where magma lies close to the surface
  • Ash ejected from volcanos can act as good fertiliser for agriculture
  • Tourism - many people want to see volcanos
  • Mining - many gemstones and metals are in relation to composite volcanos
60
Q

What is the magma chamber in a volcano

A
  • This is where the molten rock is stored beneath the ground
    *
61
Q

What is the main vent in a volcano

A

The channel which magma travels through to reach the earth’s surface

62
Q

What is the secondary vent in a volcano

A

A smaller vent in the side of a volcano where magma might escape from

63
Q

What is the crater of a volcano

A

At the top of the volcano where magma erupts from

Eddie's Geography (27 decks)

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