Key definitions
Subduction — where a denser oceanic plate sinks under a continental plate
- Boundary — where 2 plates meet
- Plate — a section of the crust; a big slab of rock on top of the mantle
Tectonic plate movement
| Feature | Convergent / destructive | Divergent / constructive | Conservative / transformative |
|---|---|---|---|
| Movement | Towards each other (can be oceanic-oceanic, oceanic-continental, or continental-continental) | Spreading | The plates slide past each other sideways |
| Relief | Trench | Ridge | No major effect |
| Activity | Earthquakes and stratovolcanoes | Earthquakes and shield volcanoes | Earthquakes |
- Subduction occurs if plates are of different densities.
- 2 continental plates of similar density leads to orogeny: fold mountain building rather than subduction.
- Most tectonic activity occurs on the area we know as the Pacific ring of fire.
Volcanoes
- Formed by tectonic movement.
- There are 2 types of volcano: stratovolcanoes and shield volcanoes.
| Stratovolcanoes | Shield volcanoes |
|---|---|
| Tall | Wide and shorter |
| Viscous lava, cools quickly | Less viscous lava |
| High pressure causes an explosive eruption | Cools slowly |
| Rocks are thrown out of the volcano | Less explosive and less acidic lava |
| Secondary cones formed when magma leaks through the sides | Often formed underwater |
Volcano case study — Mt Sinabung (Indonesia)
Located on the Indo-Australian plate (oceanic) and the Eurasian plate (continental), a destructive plate boundary.
- Agriculture contributes 14% of GDP to Indonesia.
- Agriculture is 1/3 of the labour force.
- 2010 was the first eruption after 400 years of dormancy.
- 2013 — released toxic gas.
- 2014 — erupted multiple times in January, killing 16+.
- 2015, 2016 — ash plumes were seen; destruction of infrastructure and crops.
- Tourism is 3.6% of the GDP.
Hazards and opportunities of living near a volcano
| Hazards | Opportunities |
|---|---|
| Volcano eruption | Fertile soil: ash and materials fall and settle on the land; the ground absorbs them |
| Death | Geothermal energy |
| Destruction of infrastructure | Tourism |
| Animals killed | Valuable minerals |
| Crops destroyed | Research |
| Mudflow | |
| Air pollution | |
| Costly insurance |
Earthquakes
The shaking and vibration of the earth's crust due to movement in tectonic plates.
- Focus — the precise location an earthquake occurs underground
- Epicentre — the location of an earthquake on the ground directly above the focus
- Magnitude — the amount of energy released in an earthquake
- Richter scale — the way we classify the severity of an earthquake
- Seismic waves — energy that is released by earthquakes
- Seismometer — the instrument that is used to measure the strength/amount of energy released
How an earthquake occurs (transformative plate boundary)
- 2 plates move towards each other, building up pressure in strain energy.
- Pressure builds up and the plates slide against each other, relieving the pressure in the form of seismic waves.
- The focus is where the earthquake occurs; the epicentre is the ground directly above the focus.
- As the rock settles in its new position, smaller aftershocks are sent out.
Earthquake case study — Haiti (2010)
Located on a conservative plate boundary between the North American and Caribbean plates.
- Over 220,000 killed.
- 250,000 houses destroyed.
- 3 million people displaced.
- 1300+ schools destroyed.
- Dirty water caused cholera.
- Public telephones, orphanages, the airport and hospitals damaged/destroyed.
Response:
- New industrial parks and transport projects to improve unemployment.
- Replacing charcoal as a fuel and reforestation to help slow soil erosion and to make fertile soil.
- Replacing the machete with machinery to increase crop yields.
Reducing the impact of tectonic hazards
| Volcanoes | Earthquakes |
|---|---|
| Predict, using historical events | Use a seismometer to detect changes |
| Monitor: gases in air, temperature, animal behaviour | Monitor: ground movement |
| Educate the public and practice evacuation drills | Educate the public and practice evacuation drills |
| Prepare food and aid kits | Prepare food and aid kits |
| Build earthquake-proof buildings |
Earthquake-proof building features:
- Bird-cage steel structure to prevent collapse.
- Shutters that fall automatically.
- Reinforced lift shafts with tension cables.
- Rolled weights on the roof.
- Open spaces for people to gather.
- Lattice steel foundation that is forced into bedrock.
- Rubber shock absorbers in between the ground and building.