Plate Tectonics

Question 1

What is a ‘natural hazard’?

Answer 1

A naturally occurring event that threatens human lives and causes damage to property.

Question 2

Describe the characteristics of the Core with respect to its thickness and whether it is in the solid or liquid state.

Answer 2

Approximately 1,400 km thick. The inner core is solid due to the extreme pressure exerted on it. The outer core on the other hand is a liquid layer of approximately 2,100 km thick.

Question 3

Describe the characteristics of the Mantle with respect to its thickness and whether it is in the solid or liquid state.

Answer 3

The mantle is approximately 2,900 km thick and is made up mostly of solid rocks that flows under high temperatures and pressure.

Question 4

Describe the characteristics of the Crust with respect to its thickness and whether it is in the solid or liquid state.

Answer 4

The crust is made up of the oceanic and continental crusts, ranging from a few km thick to more than 70km thick. It is generally in the solid state.

Question 5

Explain the movement of tectonic plates due to convection currents.

Answer 5

Convection currents are movements of heat within the mantle. material in the mantle is heated by the core, causing the mantle material to expand, rise and spread out beneath the plates.
This causes plates to be dragged along and to move away from each other.
Then, the hot mantle material cools slightly and sinks, pulling the plates along.
The sinking mantle material heats up again as it nears the core and the whole process repeats.

Question 6

Explain the movement of tectonic plates due to slab-pull force.

Answer 6

Slab-pull force occurs when the dense, sinking oceanic plate at subduction zones pulls the rest of the plate behind it. This drives the downward portion of the convection currents.

Question 7

Explain the formation of landforms at oceanic-oceanic divergent plate boundaries. Provide an example of the landform(s).

Answer 7

1. Convection currents cause two oceanic plates to move apart, forming a divergent plate boundary.
2. Magma rises from the mantle at the zone of divergence to create a ridge of new ocean floor between the plates as they move apart, in the process known as sea-floor spreading.
3. This forms a mid-oceanic ridge, which is a central ridge structure that divides the ocean basin in half, with the newly formed rocks closest to the mid-oceanic ridge.
4. At various points along the mid-oceanic ridge, magma builds up and solidifies to form undersea volcanoes.
5. When these volcanoes eventually grow above sea level, they are known as volcanic islands.
6. An example is the Mid-Atlantic Ridge in the middle of the Atlantic Ocean, formed when the North American Plate and the Eurasian Plate moved away from each other.

Question 8

Explain the formation of landforms at continental - continental divergent plate boundaries. Provide an example of the landform(s).

Answer 8

1. Convection currents cause two continental plates to move apart, forming a divergent plate boundary.
2. The two continental plates are stretched, causing fractures to be formed at the plate boundary.
3. As the crust continues to be pulled apart, the land in between the two continental plates sink, forming a linear depression known as a rift valley.
4. The remaining highland next to the rift valley is known as a block mountain.
5. An example is the East African Rift Valley, formed when the Nubian boundary of the African plate moved away from the Somalian boundary of the African plate.

Question 9

Explain the formation of landforms at oceanic - oceanic convergent plate boundaries. Provide an example of the landform(s).

Answer 9

1. Convection currents cause two oceanic plates to move towards each other, forming a convergent plate boundary.
2. The denser oceanic plate subducts under the less dense oceanic plate, forming a subduction zone.
3. At the subduction zone, a depression in the sea floor called an oceanic trench is created.
4. At the same time, the denser subducting plate causes mantle material above it to melt, forming magma.
5. The magma rises through cracks in the crust to form volcanoes.
6. Eventually, the magma rises above the sea level to form a chain or arc of islands.
7. Earthquakes may also occur at the boundary between the two plates due to the friction created.

Question 10

Explain the formation of landforms at continental - continental convergent plate boundaries. Provide an example of the landform(s).

Answer 10

1. Convection currents cause two continental plates to move towards each other, forming a convergent plate boundary.
2. As both plates are too thick and buoyant, they resist subduction.
3. This causes the plates to break and slide along fractures in the crust.
4. Layers of rocks in the upper part of the continental crust are then compressed together and fold, creating fold mountains.
5. An example is the Himalayas, formed by the convergence of the Indian plate and Eurasian plate.

Question 11

Explain the formation of landforms at oceanic - continental convergent plate boundaries. Provide an example of the landform(s).

Answer 11

1. Convection currents cause an oceanic plate and a continental plate to move towards each other, forming a convergent plate boundary.
2. The denser oceanic plate subducts under the less dense continental plate.
3. At the subduction zone, a depression in the sea floor called an oceanic trench is created.
4. At the same time, the denser subducting plate causes mantle material above it to melt, forming magma.
5. The magma rises through cracks in the crust to form volcanoes.
6. On the other hand, layers of rocks in the upper part of the continental crust are then compressed together and fold, creating fold mountains
7. An example is the Sunda trench and Barisan Mountains, formed when the Australian plate converged with the Eurasian plate.

Question 12

Compare the characteristics of fold mountains and block mountains.

Answer 12

1. Both are formed at continental-continental plate boundaries.
2. Block mountains are formed at divergent plate boundaries while fold mountains are formed at convergent plate boundaries.
3. Fold mountains tend to be taller than block mountains.
4. Fold mountains are formed by folding while block mountains are formed by faulting.

Question 13

Describe the characteristics of shield volcanoes.

Answer 13

1. Gentle slopes
2. Formed by less viscous lava
3. Formed at divergent oceanic - oceanic plate boundaries
4. Less violent eruptions

Question 14

Describe the characteristics of stratovolcanoes.

Answer 14

1. Steep slopes
2. Formed by viscous lava
3. Formed by the alternating eruptions of ash and lava
4. Formed at convergent oceanic - oceanic and oceanic - continental plate boundaries
5. Violent eruptions with ash and pyroclasts

Question 15

Explain how tsunamis are formed.

Answer 15

1. Large underwater earthquakes or volcanic eruptions lead to the movement of the sea floor.
2. The rapid movement of the ocean floor displaces a column of water.
3. A series of waves travel outward at heights less than 3 feet in the open seas.
4. As the waves approach shallower waters, friction causes them to rise in height, and crash down on the coast.

Question 16

Explain the benefits of living near volcanoes.

Answer 16

1. Fertile soils : breakdown of volcanic materials -> good for agriculture
2. Tourism : natural scenery and history attract many tourists -> income for locals involved in the tourism industry
3. Previous stones and minerals : formed after millions of years -> dug out and sold for income
4. Geothermal energy: heat from volcanoes can be used to turn turbines and generate electricity for people to use

Question 17

Explain the risks of living near volcanoes.

Answer 17

1. Massive destruction due to volcanic materials : loss of lives, homelessness, economy impact as people and government need to pay for repairs
2. Pollution : crops are suffocated, leading to food shortage. People suffer from respiratory problems.

Question 18

Explain why different places experience different extent of damage caused by earthquakes.

Answer 18

1. Magnitude: Greater amount of seismic energy received, more shaking of the ground and more destruction.
2. Distance from epicentre: Nearer to epicentre, experience more seismic energy, more shaking of the ground and more destruction.
3. Time: Affects what the people will be doing. If it is at night, the people will be sleeping and less aware, thus chances of evacuating will be lower. If the earthquake occurs in the city during the day, many people will be affected as they would be working or going about their daily lives there.
4. Type of soil: Unconsolidated soil will liquify, causing buildings to collapse easily and cause more destruction.
5. Level of preparedness: Determines if the people know what to do in times of an earthquake and thus be able to evacuate on time. Also determines if the country has in place enough mitigation measures.
6. Population density: Higher population density suggests more tall buildings which could collapse, causing greater destruction.

Question 19

Explain the impacts caused by earthquakes.

Answer 19

1. Disruption of services -> economy affected; aid cannot be received on time leading to more deaths and injuries
2. Landslides -> loss of lives; homelessness
3. Destruction of properties and infrastructure -> loss of lives; homelessness; economic cost of repairs
4. Loss of lives (due to buildings collapsing, landslides, tsunami)
5. Tsunamis -> loss of lives; homelessness; water-borne diseases; economic cost of repairs

Question 20

Explain how landuse regulations help mitigate the impacts of earthquakes.

Answer 20

Buildings are not allowed to be built near earthquake prone areas -> less chance of building collapsing and lower population density -> less destruction and loss of lives.

Limitation: People who are currently living near these areas may not be willing to move out. The government might have to spend lots of money to repay them, which might not be feasible.

Question 21

Explain how infrastructure development can help mitigate the impacts of earthquakes.

Answer 21

Buildings are built with damping devices or steel rods to reduce the chances of them collapsing during an earthquake -> less destruction and loss of lives.

Electrical wires and water pipes are built underground so they are not damaged during an earthquake -> communication channels are kept stable and people can seek help. The economy will also be less affected as people can continue to go to work.

Limitation: Expensive. LDCs may not be able to afford.

Question 22

Explain how emergency drills can help mitigate the impacts of earthquakes. What is its limitation?

Answer 22

With emergency drills, people know what to do in times of an earthquake -> less chaos and higher chance of people evacuating safely -> less casualty

Limitation: Complacency. People might still not be prepared if the magnitude of the earthquake is too high.

Question 23

Explain how earthquake and tsunami monitoring and warning systems can help mitigate the impacts of earthquakes. What is its limitation?

Answer 23

Earthquake and tsunami monitoring and warning systems are used by analysing past trends and patterns -> predict when an earthquake or tsunami is approaching -> people are able to evacuate -> less casualty.

Limitation: People may still not have sufficient time to evacuate; If there are too many false alarms, people might not believe it and thus it might lose its effectiveness in future.

Question 24

Explain how search and rescue can help mitigate the impacts of earthquakes. What is its limitation?

Answer 24

Search and rescue means the immediate search of survivors after an earthquake, usually through sniffer dogs. With more people rescued as soon as possible, there should be less casualties.

Limitation: Rescuers have a limited time to conduct the search and rescue as the people trapped are unable to survive long without food, water and air.

Question 25

Explain how emergency, food and medical supplies can help mitigate the impacts of earthquakes. What is its limitation?

Answer 25

The injured are treated and clean drinking water is provided to survivors to prevent dehydration and the spread of diseases. Provision of immediate aid helps survivors continue with their lives.

Limitation: Medical supplies, food and water may not be sufficient and this may cause social unrest.

Question 26

Explain how rebuilding of infrastructure can help mitigate the impacts of earthquakes. What is its limitation?

Answer 26

Infrastructure and amenities are rebuilt and improved upon after a disaster. Stricter building codes are developed to ensure infrastructure is restored at a higher safety level than before.

Limitation: Reinforced buildings built to protect against earthquakes, are not necessarily protected against tsunamis.

Question 27

Explain how provision of healthcare can help mitigate the impacts of earthquakes. What is its limitation?

Answer 27

Health options such as long-term counselling are provided because the loss of loved ones, homes or jobs after earthquakes can cause long-lasting trauma.

Limitation: Improving health options and restoring the resilience of people after an earthquake can be very challenging.