Question: Where is the lava coming from?

Rebecca Williams answered on 24 Jun 2014:

Hi Rhian,
Lava is magma that has been erupted onto the Earths surface. Magma is stored in magma chambers underneath volcanoes – these are areas of partly molten rock under the ground.

To make magma you have to melt rock which is in a layer underneath the Earth’s crust, called the mantle. Did you know the Earth was made of layers? You can see a pitcure of this here: The mantle can move very slowly and the Earths crust is carried on top of it. The crust is broken up into tectonic plates – when they bash together you get earthquakes.

You can melt the rock in the mantle in different ways.
1) Heat it up. Sometimes you get plumes of very hot material coming up from the Earths core, and this melts the mantle forming volcanoes like Hawaii. Like this:

2) Reduce the pressure. Rocks in the mantle are under a lot of pressure. When you decrease this pressure, they melt. You can decrease pressure in the mantle by moving the Earths crust apart at a plate boundary, like this: http://a.files.bbci.co.uk/bam/live/content/zjrvcdm/small These are called mid-ocean ridges and are under oceans like the Atlantic. The volcanoes formed here make up the longest mountain chain in the world!

3) Add water. Mantle is normally dry, if you add water you can help melt it. When two tectonic plates of the Earth’s crust bash together, one plate slides under the other. Its normally the crust that has the ocean on it that goes under the one with the land. When the plate goes down, it takes water with it. It also rubs with the other plate making lots of heat. This melts the mantle which then rises up as magma to make a volcano. This is called a subduction zone and looks like this: