Investigating the causes and consequences of earthquakes and featuring case studies from Haiti and New Zealand.
The solid ground that we all live on forms a thin crust around the Earth. It’s no more than 50km thick - and it’s just the upper part of the lithosphere.
Below it is the upper mantle. It’s mostly solid rock, moving under extreme pressure and heat.
The planet’s continents and ocean floors are constantly being pushed and pulled. They're divided into seven major tectonic plates – and many smaller plates.
The zones between them are known as plate boundaries…and they can be dangerous places.
A destructive boundary occurs when two plates are pushed towards each other.
There are two types of destructive boundary. In a collision boundary, the plates push against each other so that layers of rock shear, buckle, and fold.
In a subduction boundary, one plate slides below the other. The slabs of the Earth’s crust that are thrust down into the mantle create pull, or suction patterns in the hotter, more pressurised surrounding rock - forces which continue to pull the plate down into the subduction zone.
Where plates are moving away from each other, they form constructive boundaries - weak points at which molten rock can escape up to the surface, where it cools, and forms new crust.
Some plates slide alongside each other, travelling in different directions. These are conservative boundaries.
At all of these different kinds of boundary, movement is very slow - but the forces are enormous. Friction locks layers of rock together - but pressure builds, gradually and relentlessly.
When the pushing and pulling forces of the plates become too great for the holding forces of friction, movement occurs - suddenly - as stored energy is released.
These events are called earthquakes…and their impact can be extreme.
The country of Haiti sits very close to the boundary of the Caribbean plate. On 12 January 2010 the area experienced a huge, magnitude seven earthquake, coming from 13 km below ground level.
Beneath the south island of New Zealand, the Pacific plate is being subducted under the Australian plate. On 22 February 2011 a magnitude six shock struck, caused by lateral movement in a fault at the edge of the plate. The shock came from just 5 km below ground level and was very close to the city of Christchurch.
In the case of the Haiti earthquake, the impact was devastating. Haiti is one of the lowest income countries in the world. Buildings were constructed with limited resources. People were crowded into dense city areas. And this meant that the ground shocks were deadly.
The earthquake hit close to the capital of Port-au-Prince. At least 280,000 buildings were destroyed and around 200,000 people were killed.
Survivors had to sleep out in the streets, while aftershocks continued…and the Haitian government was dependent on international humanitarian aid and assistance, after many of its own buildings were destroyed.
In New Zealand, the city of Christchurch was also severely affected. Foundations were destroyed, 80% of the water and sewerage system was severely damaged and 185 people were killed.
Because Christchurch is a city with a far lower population density, and because New Zealand is a high income country with strict rules on how buildings are constructed, the impact - compared to the Haiti quake of 2010 - was far less deadly.
So tectonic forces can be powerful enough to wipe out hundreds of years of human effort in just a few seconds…but how the impacts are felt depends on local conditions.
The video
Plate tectonics: Earthquakes
Download/print a transcript of this episode (pdf).
This video explores the structure of the Earth and how the lithosphere is split into seven major plates and many minor plates.
Between the plates are plate boundaries and this video introduces destructive, constructive and conservative plate boundaries and how the plates move at each of these, with earthquakes occurring as a result of plate boundary movement.
In 2010 a major earthquake caused widespread destruction in Haiti and in 2011 a powerful earthquake rocked Christchurch in New Zealand. The video compares the impact of the two earthquakes and how the outcome of tectonic events can differ depending on location, population density and level of development.
Teacher Notes
Download/print the Teacher Notes for this episode (pdf).
Teacher Notes prepared in partnership with the Geographical Association.
Before watching the video
- Ask students to draw the structure of the Earth. What do they already know about the different layers found inside the Earth?
- Discuss how the structure of the Earth is linked to earthquakes. Ask students to suggest how earthquakes occur. If they are unsure, ask them to make a prediction and to write this down. Students can add to this once they have watched the video.
- Ask students to create a spider diagram of the impact of an earthquake. Students could categorise this into social, economic and environmental impacts.
- Introduce key terms such as:
Mantle: the layer of semi-solid rock that sits between the crust and the core, beneath the Earth’s surface.
Lithosphere: the rigid, outermost layer of the Earth, made up of the crust and upper mantle.
Subduction zone: the point at a destructive plate boundary where one plate slides beneath the other.
Magnitude: a measure of the size of an earthquake or the amount of energy released by an earthquake.
Population density: the number of people living per square kilometre in a location.
While watching
You may wish to stop at relevant points during this short video to pose questions and check understanding, or wait until the end. Useful questions might include:
- What is the lithosphere?
- What happens at a destructive plate boundary?
- What is a subduction zone?
- What happens at a constructive plate boundary?
- What happens at a conservative plate boundary?
- What causes an earthquake?
- What caused the earthquake in Haiti?
- What were the impacts of the earthquake in Haiti?
- What caused the earthquake in Christchurch?
- What were the impacts of the earthquake in Christchurch?
- What factors can affect the impacts of an earthquake?
After watching
- To help with their understanding of plate boundaries, students should draw out the different plate boundaries and the processes that occur at each. Students could research where these plate boundaries can be found - for example, there is a constructive plate boundary which divides Iceland and forms the Mid-Atlantic Ridge.
- Look at websites such as the United States Geological Survey and the British Geological Survey earthquake maps. Is there a pattern as to where the earthquakes happen? Can students map this to the plate boundary maps?
- Students could compare the impacts of the two earthquakes studied in the video and divide these impacts into ‘social’, ‘economic’ and ‘environmental’. Are there any impacts that they could add to their spider diagram from the activity before the video? Students could research a further earthquake of similar magnitude - for example, the 6.5 magnitude earthquake that hit Aceh in Indonesia in 2016.
Where next?
- What could be done to reduce the impacts of earthquakes? Some countries - such as Japan - have specially-built infrastructure which is designed to reduce the impact of an earthquake. This includes using damping, cross braces and flexible foundations.
- Students could research what has been done in countries across the world and use these ideas to help them to design their own earthquake-proof buildings. These could also be turned into 3D structures with groups of students building them in teams.
Links
Plate tectonics:
https://www.bbc.co.uk/bitesize/topics/zn476sg/articles/zrcgr2p
Plate margins and plate tectonics:
https://www.bbc.co.uk/bitesize/topics/zqvb7v4/watch/zyk46rd
Earthquakes and tsunamis:
https://www.bbc.co.uk/bitesize/topics/zn476sg/articles/zc4rcmn
Earthquakes:
https://www.bbc.co.uk/bitesize/guides/zp46sg8/revision/1
Haiti earthquake:
https://www.bbc.co.uk/bitesize/guides/zp46sg8/revision/4
Curriculum notes
This video is suitable for teaching KS3 in England and Northern Ireland, 3rd/4th Level in Scotland and Progression Step 4 in Wales.
In the English National Curriculum this film can be used to help teach the following:
- Physical geography relating to geological timescales and plate tectonics.
Resources
Teacher Notes
Download/print the Teacher Notes for this episode (pdf).
Transcript
Download/print the transcript for this episode (pdf).
