tectonic hazards

Question 1

describe the continental drift theory:

Answer 1

• proposed by Alfred Wegener
• suggested the continents were not always in the same position as they’re in today.
• at one point in time, all the continents were joined together as one large mass of land.
• there are similar patterns of rocks and fossils on both sides of the Atlantic, suggesting that they were once joined.
• includes fossil remains of land mammals which wouldn’t have been able to swim across from one side to the other.

Question 2

what are tectonic hazards?

Answer 2

threats caused by the movement of tectonic plates that have the potential to cause damage to life, property, or the environment. examples include volcanoes and earthquakes.

Question 3

describe the global distribution of earthquakes:

Answer 3

earthquakes usually occur at plate margins due to enormous pressure build-up. however, there are anomalies that don’t occur on plate margins, and these are caused by human activity e.g. underground mining.

Question 4

describe the global distribution of volcanoes:

Answer 4

the majority of volcanoes run along plate margins. e.g. pacific ring of fire, mid-atlantic ridge.

Question 5

how are volcanoes generally formed?

Answer 5

hot, molten rock (magma) rises to the surface at constructive and destructive plate margins, forming volcanoes.
- they can also form in ‘hot-spots’, where the crust is thin enough for magma to break through it.

Question 6

describe the difference between oceanic and continental crust:

Answer 6

oceanic crust:
- dense
- thin (5-10km)
- younger
- can be destroyed

continental crust:
- less dense
- thick (20-200km)
- older
- cannot be destroyed

Question 7

describe convection currents:

Answer 7

the Earth’s core is hot and this heats the mantle. the heated magma rises as it is less dense. as it rises, it cools and becomes denser again.
this creates a circular movement within the mantle (convection currents). the plates sit atop the mantle and the convection currents drag the plates along.

Question 8

describe ridge push and slab pull:

Answer 8

ridge push:
- mid-ocean ridges are higher than the rest of the ocean floor so gravity causes the ridge to force the plate down

slab pull:
- tectonic plates are heavy. when a plate begins to subduct (sink), gravity means that it’ll pull the rest of the plate down with it.
> it’s always the oceanic plate that’s subducted beneath the continental plate.

Question 9

why are earthquakes hazardous?

Answer 9

• the ground shakes, causing buildings to collapse
• water and gas pipes are damaged, causing fires and floods

Question 10

why are volcanoes hazardous?

Answer 10

• ash clouds disrupt air travel and can make it difficult and dangerous for planes to fly
• ash can also cover farmland, covering and damaging the crops underneath
• heavy ash can also, in some cases, cause buildings to collapse

Question 11

what occurs at a constructive plate margin?

Answer 11

plates move apart. new crust is formed as magma rises to the surface. the process’s friction causes earthquakes, but the end result is typically broad and flat shield volcanoes, as the magma is hot and fluid, and flows a long way before cooling.

Question 12

what occurs at a destructive plate margin?

Answer 12

plates move towards each other. the denser oceanic plate subducts (sinks) beneath the less dense continental plate. gravity pulls the oceanic plate into the mantle. friction between the two plates causes earthquakes. the end result is a steep-sided, composite volcano, that’s violent and explosive.

Question 13

what occurs at a conservative plate margin?

Answer 13

the plates are moving past each other (usually one is going at a different speed to the other). friction between the plates causes earthquakes. there are no volcanoes because there is no magma.

Question 14

what occurs at a collision plate margin? (linked to destructive plate margins)

Answer 14

two continental plates meeting doesn’t result in subduction. instead, the two plates collide, the crust is crumpled and uplifted, and results in mountains. these processes cause earthquakes, but no volcanoes as there is no magma.

Question 15

why do people choose to live on plate margins? what are the benefits?

Answer 15

• better building designs can withstand earthquakes, so people feel less at risk.
• volcanoes can bring benefits e.g. fertile soils, rocks for building, rich mineral deposits, hot water.
• more effective monitoring of volcanoes and earthquakes can allow people to receive warnings and evacuate before events happen.

Question 16

what is life like on a plate margin in iceland?

Answer 16

• geothermal electricity generates 25% of the country’s power.
• hot water from the Earth’s crust provides heat and hot water for 90% of iceland’s houses.
• thousands of tourists visited iceland after a volcanic eruption in 2010.

Question 17

describe the chile earthquake:

Answer 17

• 27th february 2010
• 8.8 on the richter scale
• just off the coast of chile
• destructive plate margin, so it occurred at sea. tsunamis raced across the ocean at 800km/h

Question 18

describe the nepal earthquake:

Answer 18

• 25th april 2015
• 7.9 on the richter scale
• shallow earthquake (15km deep) meaning there was very severe ground shaking and widespread avalanches and landslides

Question 19

what were the primary and secondary effects of the chile earthquake?

Answer 19

primary:
- 500 killed, 12,000 injured

secondary:
- 1500km of roads were damaged due to landslides - remote communities were cut off
- several pacific countries were struck by tsunamis

Question 20

what were the primary and secondary effects of the nepal earthquake?

Answer 20

primary:
- 9,000 killed, 20,000 injured. over a third of nepal’s population was affected
- 3 million people left homeless
- 1.4 million people needed food, water and shelter

secondary:
- avalanches in the langtang region left 250 people missing
- ground shaking caused landslides, blocking roads, hampering relief efforts
- avalanches on mt. etna killed 19 people

Question 21

what were chile’s immediate and long-term responses to the earthquake?

Answer 21

immediate:
- power and water restored to 90% of homes within 10 days
- national appeal raised $60 million to build 30,000 emergency shelters
- international aid: satellite phones, floating bridges supplied

long-term:
- chile’s strong economy (from copper exports) was able to rebuild itself without much foreign aid
- 1 month after the earthquake, chile’s government launched a housing reconstruction plan to help 200,000 affected households

Question 22

what were nepal’s immediate and long-term responses?

Answer 22

immediate:
- search and rescue teams, medical support arrived from different countries
- field hospitals set up to help overcrowded main hospitals.
- 500,000 tents provided to help the homeless

long-term:
- stricter controls on building codes
- in june 2015, nepal set up an international conference to discuss reconstruction and seek international technical/financial aid

Question 23

define management strategies:

Answer 23

helps to reduce the effects of natural hazards such as death, injury, unemployment.

e.g. 750,000 people live at the foot of mt. fuji, so it is important to use management strategies to keep them safe.

Question 24

describe the management strategy of monitoring for volcanoes:

Answer 24

scientists can monitor volcanoes for signs that can indicate when an eruption will take place.
- ground deformation: 400 monitoring stations with tilt meters and laser mapping technology record ground deformation.
- escaping gases: a team monitor mt. fuji to collect volcanic gas samples (e.g. co2, sulphur dioxide).
- seismic activity: a network of 800 seismometers across japan detect and locate local seismic activity, which could indicate a possible eruption.

Question 25

describe the management strategy of monitoring for earthquakes:

Answer 25

• generally occur without warning
• scientists have yet to discover reliable ways in monitoring earthquakes other than minor tremors and ground deformation

Question 26

describe the management strategy of prediction for volcanoes:

Answer 26

• based on scientific monitoring
• in 2010 eruption in Iceland, scientists could detect an increase in earthquake activity, allowing them to make accurate predictions about the eruptions that occurred that year

Question 27

describe the management strategy of prediction for earthquakes:

Answer 27

scientists study historical records of earthquakes at plate margins, and have identified locations that they believe are at the greatest risk.

Question 28

describe the management strategy of protection for volcanoes:

Answer 28

earth embankments or explosives can divert lava flow away from valuable property. this has been done on the slopes of mount etna.

Question 29

describe the management strategy of protection for earthquakes:

Answer 29

• construct buildings that are resistant to the ground shaking from an earthquake. in chile, new buildings have concrete columns with a steel frame.
• regular earthquake drills and tsunami walls help to protect houses and power stations.

Question 30

describe the management strategy of planning for volcanoes:

Answer 30

• hazard maps are produced for areas that are likely to be affected
• this can restrict certain land uses, or identify areas that need to be evacuated when an eruption is imminent
• this data is based on past eruptions

Question 31

describe the management strategy of planning for earthquakes:

Answer 31

maps are produced to show the effects of an earthquake or identify areas most at risk. high value land can then be protected. people in earthquake areas can be drilled on what to do, and buildings are constructed to be earthquake proof.
- emergency services are trained
- evacuation routes can be planned

Question 32

how can buildings be designed to withstand earthquakes and volcanoes?

Answer 32

• reinforced concrete can absorb an earthquake’s energy (preventing buildings from collapsing and therefore saving people from being crushed)
• buildings can be strengthened with steel frames, making them less likely to collapse and less people being injured
• automatic shut-off valves can turn off gas and electricity to prevent fires