Topic 3: Tectonic plates

Question 1

What are the tectonic plates made of?

Answer 1

The oceanic lithosphere and the thicker continental lithosphere.

Question 2

Name the 3 movements of the tectonic plates, and explain each one. Give an example of each.

Answer 2

1. Converge - move towards each other and collide.
   E.g. The Himalayan Mountains.
2. Diverge - move away from each other.
   E.g. The Great Rift Valley in Africa.
3. Transform - glide past each other.
   When this happens, earthquakes are caused.
   E.g. The February 2010 earthquake in Chile.

Question 3

How and why do volcanoes occur?

Answer 3

When the tectonic plates collide, one plate can slide under the other. This can cause the mantle to melt and become magma. The magma pushes upwards, through cracks and weak points in the crust, melting more rock. The hot magma collects under the surface of the earth in magma chambers. In addition, it is so hot deep inside the Earth, that some rocks slowly melt and become a thick flowing substance, also called magma. Magma is lighter than the solid rock around it, so it rises and also collects in magma chambers.

When the pressure id high enough in the magma chamber, or if a crack opens in the crust, the magma is forced up the vent and shoots out of the crater. This is called an eruption. Eruptions can cause lava flows, hot ash flows, mudslides, avalanches, falling ash and floods.

The type of eruption and the material that makes up the magma determines the size and type of volcano that is formed.

Question 4

Name the 3 types of volcanoes.

Answer 4

1. Shield - long, flat volcano.
2. Cinder cone - small volcano.
3. Composite - cone shape.