Plate tectonics, earthquakes and volcanoes

The Structure of the Earth, the Layers
1. Structure
  1. The Earth has four main layers – the inner core, the outer core, the mantle and the crust
  2. The inner core is 5,500°C - extremely hot. It is a very dense solid made from iron and nickel.
  3. The outer core is 2,000 km thick and is a liquid.
  4. The mantle is semi-molten and about 3,000 km thick.
  5. The crust is the rocky outer layer.The crust is made up of pieces called plates. There are two types of crust: oceanic and continental crust. The oceanic crust is found under the sea and is thinner and less dense than the continental crust.
2. Plate Movement
  1. Earthquakes and volcanoes are primarily found at plate boundaries. Convection currents in the mantle drive them to move. The mantle is much hotter than the crust and its rock is molten. At the boundaries between plates, molten magma is able to force its way to the surface and escape as lava.
What happens to the crust at plate boundaries?
1. Heat from the core causes convection currents in the mantle. These currents slowly move the crust around. In some places the crust is destroyed. In other places new crust is formed.
The effects of earthquakes on people
1. 3 million people affected.
2. Over 220,000 deaths.
3. 300,000 injured.
4. 1.3 million made homeless.
5. Several hospitals collapsed.
6. 30,000 commercial buildings collapsed.
7. Businesses destroyed.
8. Damage to the main clothing industry.
9. Airport and port damaged.
Earthquakes
1. Large earthquakes are usually connected with plate boundaries. Earthquakes happen often but most are too small for us to notice. Seismometers record earth movements.
2. An earthquake is a sudden shockwave caused by rocks being under stress from the movements of plates at plate boundaries, and this stress builds up until it reaches breaking point, and all the energy stored up is released in the form of shockwaves.
3. In the past, the Richter scale was used to measure the power of earthquakes. Earthquakes are now measured using the Moment Magnitude Scale which measures the size of the seismic waves during the earthquake. Each step in the scale is ten times greater than the previous number.
4. The Mercalli Scale measures the damage caused by an earthquake, the intensity, and changes according to which area you are measuring.
Volcanoes
1. A volcano is an opening in the Earth’s crust. It allows hot magma, ash and gases to escape from below the surface.
2. Composite Volcanoes
  1. Steep-sided and cone-shaped, made up of layers of ash and lava and containing sticky lava which doesn’t flow very far.
  2. Mount Etna in Italy is a composite volcano.
3. Shield Volcanoes
  1. Have gently sloping sides and runny lava that covers a wide area. Gases escape very easily from shield volcanoes.
  2. Mauna Loa in Hawaii is a shield volcano.

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