Thank you Silas and Zakk for your question. My team are correct it’s all about pressure. All volcanoes have a thin ‘lid’ of solid rock which which is solidified magma. Underneath the lid is lots of molten magma which is heated by the Earth’s central core.
Things can happen to this magma. Some of it could cool, and solidify. You could also get convection currents like you do in any hot liquid. These can increase the pressure (push) on the volcano lid, break it and the pressure is released like the liquid in a bottle of fizzy drink.
Want to make a comment, please make it in the box below. Not sure about something …ask another question.
(Anyone reading this post who wants to ask a question or make a comment please feel free to do so)
(revised 13/9/17 Magna misspelling and added support text)