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A-Level AQA Geography > Hazards: Seismic Hazards (theory of tectonic plates & volcanic hazards) > Flashcards

Hazards: Seismic Hazards (theory of tectonic plates & volcanic hazards) Flashcards

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1
Q

What are the 4 layers of the Earth?

A

Inner core = solid ball, iron and nickel (6000ºC)
Outer core = semi-molten, iron and nickel
Mantle = silicate rock, mostly rigid (top layer is called the Asthenosphere, semi-molten)
Crust = oceanic crust (thin and dense) and continental crust (thick and light), rigid top part of the mantle and crust is called the lithosphere

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2
Q

Why is the core and mantle so hot?

A

heat energy left over from when the Earth was formed and some comes from radioactive decay
- main source of internal energy because of this

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3
Q

Evaluate the evidence for the theory of continental drift: oldest evidence?

A
  • Mostly geological evidence, the weakest of all evidence
  • apparent closeness of the coastlines of South America and West Africa suggests they were once joined
  • Mountains and rock types found to be identical from the Appalachian mountains (Eastern USA) to the UK, Scandinavia and North-West Africa, suggests joining
  • overall suggests that the supercontinent Pangea existed
  • no explanations of how continents move
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4
Q

Evaluate the evidence for the theory of continental drift: Following WW2?

A
  • Biological evidence
  • Sonar studies of seafloor -> areas of mountains & valleys found underwater in oceans
  • change in Earth’s polarity creates striations on either sides of ocean ridges
  • provided evidence for sea-floor spreading (only one reason)
  • showed crusts were getting bigger
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5
Q

Evaluate the evidence for the theory of continental drift: Today?

A
  • satellites accurately measure global movement of places, 2-20cm per year on average
  • seismometer readings show clear patterns following edges of tectonic plates
  • Modern technology allows us to witness plate movement in real time accurately, evidence of Wagner’s theory grows stronger
  • However, this evidence doesn’t completely conclude how the plates are moving
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6
Q

What is the theory of continental drift?

A
  • published by Wagner in 1912
  • He suggests that 300 million years ago the supercontinent Pangea split and land masses started to move into current positions today
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7
Q

What are the 3 main drivers of plate tectonics?

A
  1. Convection Currents (mantle convection)
  2. Ridge Push (gravitational sliding)
  3. Slab Pull
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8
Q

How does convection currents drive tectonics?

A
  • hotspots around Earth’s core generate thermal convection currents in asthenosphere
  • warmer less dense material rises to cool and sink
  • this causes magma to rise up towards the crust and spread before sinking
  • this is the main driver of movement in the lithosphere and crust by FRICTION between asthenosphere and lithosphere which pulls/drags plates
  • doesn’t account for different rates of plate movement
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9
Q

How does ridge push drive plate tectonics?

A
  • rising magma pushes ridge higher than seas floor, so the thickness and weight of rock push down and out on the crust due to gravity
  • this speeds up the process of sea-floor spreading
  • accelerates the moving of the plate
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10
Q

How does slab pull drive plate tectonic?

A
  • weight and density off descending slab at destructive plate boundary is higher than the surrounding material so it sinks
  • gravity-generated force pulls subducting plate down adding to speeding up of movement
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11
Q

What processes are occurs at a Destructive Plate Boundary?

A
  • Magma convection (friction) of opposite continental plate and oceanic plate so they’re pushes together
  • slab pull as gravity generated force increase speed of subduction of oceanic plate (more dense so it sinks)

Friction and subduction

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12
Q

What are some examples of destructive plate boundaries?

A

Eurasian and Indian plate

Nazca and South American plate

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13
Q

What processes are occuring at constructive plate boundaries?

A
  • Mantle convection creates friction between asthenosphere and lithosphere which pulls the plates
  • new crust being formed by rising magma
  • ridge push, gravitational force downwards of the ridge formed will create a push
  • sea-floor spreading -> mid atlantic ridge
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14
Q

What are some examples of destructive plate boundaries

A

Nazca and Pacific Plates

South American and African plate

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15
Q

What is happening at a conservative plate boundary?

A
  • Plates are moving at different speeds because there are different magnitudes of force of slab pull and ridge push on the plate (push and pull forces)
  • they push past each other at different speeds
  • lithosphere is never created or destroyed
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16
Q

What is the case study of a volcanic eruption in a country with high HDI?

A

Eyjafjallajokull (E15) Volcanic Eruption in Iceland April 2010

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17
Q

What were the characteristics of the hazard in Iceland volcanic eruption?

A
  • 4 on VEI scale
  • constructive plate boundary on a hotspot
  • Basaltic and Andesitic lava (low viscosity)
  • stratovolcano that was covered by glacier
  • interaction between lava and ash creates huge ash clouds
  • eruption lasted for over a month
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18
Q

What were the characteristics of the place/people in Iceland volcanic eruption?

A
  • 28th richest country
  • nobody lives below the poverty line
  • extensive management, e.g. land use planning and education
  • rural area is sparsely populated
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19
Q

What are the facts about the disaster in the Iceland volcanic eruption?

A
  • 0 deaths
  • 1000 evacuation
  • £130 million per day cost to the airlines that had to suspend flights
  • homes and infrastructure damage
  • crops damaged
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20
Q

What action was taken pre-disaster in Iceland?

A
  • used the hazard response cycle: risk mapping to inform settlement planning
  • scientists mitigating and monitoring the volcano
  • community preparation and education
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21
Q

What actions were taken during the response in Iceland?

A
  • bringing animals and securing homes in rural areas
  • closing roads in case of lahars (roads designed to be swept away)
  • evacuation
  • exclusion zone in Iceland and air space due to ash cloud
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22
Q

What actions were taken post disaster in Iceland?

A
  • rebuilding homes (insurance)
  • lessons taken into account for future management
  • studying the eruption to understand it more (ie. the ash plumes)
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23
Q

What is the case study of a volcanic eruption in a low HDI country?

A

Mt Nyiragongo, Congo, January 2002

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24
Q

What were the characteristics of the hazard at Mt Nyiragongo?

A
  • 1 on the VEI scale
  • constructive plate boundary
  • large basaltic stratovolcano
  • lava flow of 90km/ph
  • earthquake of 5 on Richter scale
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25
Q

What was the evidence of a disaster at Mt Nyiragongo?

A
  • 147 fatalities
  • 1/3 Goma destroyed
  • 350 000 fled to neighbouring Rwanda
  • Public disorder
  • drinking water poisoned
26
Q

What were the characteristics of Congo?

A
  • dense urban population in Goma 15 km away
  • 228th richest country
  • 68% living below the poverty line
  • in the midst of recovering/living through a civil war that caused 5 million deaths, from 1994 to 2003
  • eastern areas still were plagued with violence by rebel groups, UN peacekeeping mission there
27
Q

What action was taken in the pre-disaster period in Congo?

A
  • no action or monitoring taken even after tremors started
  • all warning signs of eruption were ignored
  • no preparation due to weak local government
28
Q

What happened during the response to the eruption in the Congo?

A
  • looting
  • 350 000 fled to Rwanda (no resources)
  • $15 million donated from Red Cross
  • evacuation ‘red alert’ issued
  • shelter and food from agencies
  • UN set up emergency shelter, health care and any essentials
29
Q

What happened post-disaster in the Congo?

A
  • No long term aid for recovery due to Congolese Civil War
  • extremely slow return to normality, long emotional recovery as they had to wait until lava cooled to bury bodies
  • 320 000 left homeless
30
Q

Q: Evaluate the effectiveness of the hazard management cycle in mitigating the impact of volcanic eruptions [20 marks]

A

It is/it is not effective effective…

  • evidence of an eruption impact being mitigated (or not) by management
  • how effective was planning in enabling this mitigation
  • can you make reference to the different stages of model?

Conclusion:
Not effective in mitigating impacts
- only wealthy countries are able to utilise the cycle
- only a format, useless when not being used

31
Q

Q: ‘It is possible to manage the impacts of volcanic eruptions, but the impacts cannot be prevented’ To what extent do you agree with this view? [20 marks]

A

Agree:

  • impacts cannot be prevented
  • iceland case study, still had impacts despite extensive management

Disagree:

  • isn’t always possible to manage impacts
  • depends on the capacity of the place to cope with the impact
  • use Congo case study
32
Q

How are ocean ridges formed?

A
  • underwater constructive plate boundary move apart allowing for upwelling magma from mantle to reach surface
  • magma cools and forms new crust as a ridge
  • new ridge forces down on plate causing sea-floor spreading
  • underwater volcanoes can form, and build up to form islands (e.g. Surtsey an Icelandic Island)
  • e.g. Mid Atlantic Ridge
33
Q

What are magma plumes?

A
  • vertical column of extra-hot magma that rises up from the mantle
  • form many connection cells all over the planet, these move plates in different directions
  • only a few strong enough to break lithosphere and create hotspot
34
Q

How do rift valleys form?

A
  • at constructive plate boundaries across continental areas
  • magma rises causes crust to bulge and fracture forming fault lines
  • areas between parallel faults become brittle and drop forming rift valleys
  • volcanoes form
  • East African Rift valley from Mozambique to Red Sea
35
Q

How do deep sea trenches form?

A
  • at destructive plate boundary
  • dense oceanic crust is forced under lighter continental crust in subduction
  • forms a very deep point of ocean
  • e.g. Marianans Trench
36
Q

How do island arcs form?

A
  • hotspots cause magma to eat into plate above
  • lava breaks through and creates underwater volcanoes which build up to form islands
  • plate moves over hotspot creating a line of volcanoes (islands)
  • e.g. Hawaiian Islands
37
Q

How do young fold mountains form?

A
  • when 2 continental plates are moving towards each other
  • lower density than underlying layers of plate so no subduction
  • sediments are forced up forming mountains
  • no volcanic activity only earthquakes
  • e.g. Himalayas
38
Q

How do volcanoes form?

A
  • the deeper a plate descends into a subduction zone the hotter the surroundings become in mantle
  • this alongside friction oceanic plates melts into magma in Benioff zone
  • less dense material in asthenosphere rises as plutons reaching the surface to form volcanoes
39
Q

What is explosivity of a volcano determined by?

A

Type of lava:
basaltic = low viscosity = more gentle (less silica)
andesitic = high viscosity = explosive (more silica)
rhyditic = high viscosity = explosive (more silica)

40
Q

What is the magnitude of a volcanic eruption measured by?

A

Volcanic explosivity index (VEI) 0 to 8 (logarithmic scale)

- doesn’t take gas emissions into account

41
Q

What is hazard intensity?

A

Measure the scale of the effects on people, human structures and the natural environment of the hazard

42
Q

What is areal extent?

A

The size/scale of the area impacted by a high

43
Q

Q: Assess the scale of an eruption.

A

Things to write about…

  • areal extent of the eruption
  • hazard intensity (effect on people, human structures and natural structures and the extent of this all, ie severe moderate etc)
  • VEI
  • physical characteristics or impacts
44
Q

Categorise the types of volcanoes…

A 
Destructive:
Dome volcano (moderate explosivity -> tend to have a high silica content)
Composite volcano (high explosivity -> lava has a high silica content and can build up high gas pressure)
Constructive:
Fissure volcano (low -> basaltic lava)
Ash-cinder (moderate -> cones form on the flanks of shield, strato and shield volcanoes)

Hotspots:
Shield volcano (low -> basaltic lava)
Caldera (High -> old cone collapsed in to orm a new cone with magma chamber below)

45
Q

What is an example of a caldera volcano?

A

Yellowstone super volcano

46
Q

Do volcanic hazards show a relationship between hazard intensity and areal extent?

A
  • primary hazards tend to have a small areal extent but a high hazard intensity
  • secondary hazards tend to have a large areal extent and a lower hazard intensity
  • lahars and tsunamis are the exceptions: lahars have a small areal extent and tsunamis having a high hazard intensity
47
Q

What are the primary hazards of a volcanic eruption?

A

Lava flows, tephra, volcanic gases and pyroclastic flows

48
Q

What are the secondary hazards of volcanic eruptions?

A

Landslides, Lahars, Tsunamis, Flooding, Acid Rain, Climatic Change

49
Q

What are pyroclastic flows?

A
  • aka nuee ardente
  • mixture of super-heated gas, ash and volcanic rock flowing down the side of a volcano at high speeds (80km/h) for long distances (10-15 km)
50
Q

What are lava flows?

A

lava flowing from the vent of the volcano, speed and distance depending on the viscosity of the lava

51
Q

What are volcanic gases?

A

CO2 and sulfur dioxide that can be humans and animals

52
Q

What is tephra?

A

solid material that is ejected by a volcano into air ranging from large volcanic bombs to fine ash

53
Q

What are lahars?

A
  • formed by volcanic ash mixing with water and flowing downhill
54
Q

What is acid rain?

A

sulphur combining with atmospheric moisture and acid rain results

55
Q

Q: Analyse the role of plate margin type in influencing the risk posed to people by volcanic hazards?

A

-

56
Q

What are the warning signs and monitoring techniques of volcanic eruptions?

A
  • Lots of small earthquakes as magma rises through crack = seismometers detect earthquakes
  • Temperatures around the volcano starts to rise = thermal imaging and satellite cameras detect heat
  • Higher sulphur content in gases = gas samples taken and chemical sensors
57
Q

What is the importance of monitoring of volcanoes?

A

allows for prediction and allows identify a time when to evacuate safely

58
Q

What are some preparation techniques of volcanic eruptions?

A
  • plan of evacuation
  • producing series of threat levels (done in NZ)
  • individual preparation
  • community search and rescue teams
59
Q

What are some protection techniques of volcanic eruptions?

A
  • identifying high risk areas (land use planning), e.g. risk assessment made for an area around Mt Rainier in USA protects 3.5 million
  • digging trenches, dropping blocks and using explosives to divert lava
60
Q

What are some adaptation techniques of volcanic eruptions?

A
  • strengthened buildings to reduce chance of collapse

- capitalise on factor of living next to volcano: farming with fertile soil or tourism industry

A-Level AQA Geography (13 decks)

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