Structure of the Earth
- 2 types of crusts; continental and oceanic
- The continental drift theory was by Alfred Wegner of which all the continents were once joined together
- Highest point; Mount Everast
- Lowest point; Morland Trench
- Until around 200 million years ago it Earth was one big land mass called Pangea
- 70% of earths surface used to be covered by water
Conservative plate boundary
- Plates slide past each other in different directions or at different rates
- The hazards found are earthquakes
- An example of conservative plate boundries are the Pacific Plate and North American Plate
Collison plate boundary
- Two continental plates converge
- The hazards found are earthquakes and fold mountains
- An example of collision plate boundries are the Indio-Autralian Plate and Eurasion Plate
Continued of Plate Boundries
Constructive plate boundary
- Where two plates (oceanic or continental) diverge
- Hazards found are shield volcanoes and earthquakes
- An example of constructive plate boundries are the North American Plate and Eurasion Plate
Destructive plate boundary
- Where an oceanic and continental plate converge
- Hazards found are earthquakes and volcanoes
- An example of destructive plate boundries are the Nazca Plate and South American Plate
Fold Mountains and Ocean Trenches.
Fold mountains are formed as the convection current causes the movement of destructive or collision plate margins to collide. The geosyncline is filled with sediments compressed into the bed rock. As the plates converge the sediments copress, this compression continues as the plates convege and the sediments fold into fold mountains between the plates.
Ocean Trenches are formed differently. One wall is formed by the subducted ocean plate, for example, the Nazca plate. The other is by the overriding continental plate, for example, the South American plate. The subduction zone is formed (ocean trench) when the heavier plate, in this case the South American plate, subducts the lighter plate.
- Formed at contructive plate margins
- As the plates move apart, magma rises from the mantle to fill the gap. This adds new rock to the spreading plates. Some of this mamga may also be forced out to the surface through a vent
- Characteristics; cone with wide base and gentle slopes, made of lava only, regular eruptions, lava pour out with little violence
Composite Cone Volcanoes
- Formed at destructive plate margins
- As the plates collide, the denser oceanic plate is pushed down into the mantle, The plate melts here and is destroyed in the subduction zone, the subduction zone the plate forns a pool of magma, the great heat and pressure may force magma along a crack where it erupts at the surface to build up a volcano.
- Characteristics; tall cone with narrow base and steep slopes, made of alternate layers of lava and ash, irregular, violent explosions
- A supervolcano is different to a normal volcano.
- It is much larger and they can be up to 80km long, 40km wide and 8km deep, emitting at least 1000km cubed of material.
- They cause a serious of volcanic eruptions known as superuption.
- They are underground. This type of volcano can empty their store of magms chamber, forming a geographic depression called a caldera.
- All earthquakes occur on plate boundries
- Many strong earthquakes occur along destructive plate margins because the great stresses build up in the subduction zone as one plate is forced down below the other. Energy is built up and released in an earthquake
- Tectonic stresses are lower along contructive plate margins because the plates move apert instead of converging; it creates land
- Primary effects consist of collapsing buildings, rocks and bridges
- Secondary effects consist of fires, tsunamis, landslides and diseases
Earthquakes are normally measured on the richter scale however the Modified Mercalli Intensity (MM) scale is a means of categorising the effects of shaking people, structures and environment. For example at 5MM things such as windows and pipes crack, but at 10MM more intense damage occurs including damage to earthquake resistant buldings and bridges