What is a volcano?
A volcano is a mountain or hill with a crater at the top leading down to magma below the earth's surface.
Why do volcanoes erupt?
Volcanic eruptions are caused when magma beneath the earth's crust begins to push towards the surface. An increase in pressure below the surface causes the magma to break through the top of the volcano. Once the magma has escaped it is called lava.
What causes the increase in pressure?
The increase in pressure below the earth's surface is caused by a variety of factors. This includes gases being formed inside a the magma chamber. The magma chamber is a large pool of molten rock below the earth's crust. The gases in the magma chamber reduce the amount of space available and the magma is pushed through the surface.
Pressure inside the magma chamber can also be caused by an increase in the amount of magma. New magma is formed from rocks and the earth's crust melting below the surface. When there is no more room for the magma below the earth's crust the pressure is too intense and it breaks through the top of the volcano.
How are volcanoes formed on the 'Ring of Fire'?
The earth's crust sits on tectonic plates. These are large pieces of land that float on the magma beneath the earth. The places on the globe where the tectonic plates meet are called convergent boundariess. Because there is a kind of gap here going down to the hot magma below, the area where these plate boundaries are found is called the Ring of Fire.
The Ring of Fire covers large parts of the world and parts of the ocean. The tectonic plates may either move towards each other and be known as subduction zones (this is also how tsunamis and earthquakes are caused) or they move apart from each other, in which case they are known as divergent boundaries.
What different type of eruptions are there?
Volcanic eruptions vary in their intensity. Sometimes lava will violently shoot into the air. Other volcanic eruptions will see thick lava run slowly down the side of the volcano.
The different types of volcanic eruptions are caused because the type of magma which has formed below the volcano is always different. Different gases and rocks are found around the world, and this causes varying types of magma.
Magma that is thick and sticky often takes longer to escape from the earth. This leads to more pressure building up inside the volcano and a much stronger eruption. However, thinner magma is able to escape from the earth much easier. In these cases, there is less pressure built up and the eruptions are weaker.