Volcanoes

A volcano is a mountain where hot gases and molten rocks break through the Earth's crust. This process is called a volcanic eruption.

 

Volcanoes have been important features of the Earth's surface for millions of years. They were probably the first landforms of the newly-formed Earth. Like all landforms, volcanoes are constantly being changed by different forces of nature. New volcanoes are constantly being formed and the old ones are being destroyed. Some existing volcanoes have been around for millions of years; others, for only a few thousand years.

Volcanic Eruptions

Volcanic eruptions usually happen in the same places. If we look at a map of the Earth's tectonic plates we will see that the majority of volcanic eruptions happen on the boundaries of these plates. That is because eruptions are caused by plate tectonics. When tectonic plates collide or pull apart, they break and change the inside layers of the Earth. When the Earth's crust breaks, the hot, liquid rock of the mantle layer 'escapes' to the surface. The mixture of molten rock, crystals and dissolved gases from the mantle is called magma. When magma erupts on to the Earth's surface, it is called lava.