What happens when they move?

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When tectonic plates slide past each other, they do not usually slide smoothly. They might get stuck for a while, and then give a bump and move very suddenly. We call the area where two plates are sliding past each other a fault line, and there are often earthquakes - these are the sudden bumpy movements made by the plates. We have fault lines going through New Zealand, and that is why we get a lot of earthquakes.

Where the tectonic plates move together, one plate slides under, and the other is forced up. This builds mountain ranges, like our Southern Alps. The rock that is forced deep under the earth gets so hot that it melts, and becomes magma. This magma can rise to the surface in eruptions, making chains of volcanoes. One of these chains is called the Ring of Fire.

When the two plates diverge, it makes deep rifts in the earth's surface, and eventually these can fill with water and become a sea or an ocean. The Red Sea is an example of this. The ocean is spread apart, and ridges are formed deep under the sea, where magma flows upward, and cools into hard rock.