Plate Tectontics

The Structure Of The Earth
1. The inner core is the hottest part of the Earth, which is solid and made up of Iron and Nickel, with temperatures of up to 5,500°
  1. The outer core is a liquid layer also made up of iron and nickel with similar to the inner core
    1. The mantle is a layer of molten rock called magma which has a diameter of 2,900 km. The upper part is hardened and the lower part is soft beginning to melt.
      1. The crust is the very outer layer of the Earth which is a solid rock and a thin layer of about 0-60 km. There are two types of crust: continental crust which carries land and oceanic crust which carries water.
Plate Boundaries
1. The Earths crust is broken up into pieces called plates. Heat rises in the mantle to cause convection currents by radioactive decay which move the plates. If the convection currents are moving inwards this causes plates move towards each other. If the convection currents move outwards the plates move away from each other.
  1. Earthquakes and volcanoes usually occur on plate boundaries, this is the point at where two plates meet.
    1. As the plates move apart slowly, magma rises from the mantle. The magma erupts to the surface of the Earth. This is also accompanied by earthquakes. When the magma reaches the surface, it cools and solidifies to form a new crust of igneous rock. This process is repeated many times, over a long period of time.
      1. At a constructive plate boundary the plates move away from each other. At a destructive plate boundary the plates move towards eachother (can be known as a collision plate boundary). At a conservative plate boundary the plates slide past each other.
    2. Constructive boundaries tend to be found under the sea, e.g. the Mid Atlantic Ridge. Here, chains of underwater volcanoes have formed along the plate boundary. One of these volcanoes may become so large that it erupts out of the sea to form a volcanic island, e.g. Surtsey and the Westman Islands near Iceland.
Compressional Boundary
1. At a compressional or destructive boundary the plates are moving towards each other. This usually involves a continental plate and an oceanic plate
2. The oceanic plate is denser than the continental plate so, as they move together, the oceanic plate is forced underneath the continental plate. The point at which this happens is called the subduction zone
  1. As the oceanic plate is forced below the continental plate it melts to form magma and earthquakes are triggered. The magma collects to form a magma chamber. This magma then rises up through cracks in the continental crust. As pressure builds up, a volcanic eruption may occur
3. As the plates push together, the continental crust is squashed together and forced upwards. This is called folding. The process of folding creates fold mountains.
  1. Fold mountains can also be formed where two continental plates push towards each other. This is how mountain ranges such as the Himalayas and the Alps were formed

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Plate Tectontics

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