Why do volcanoes erupt? – Catalysis Zone

Question: Why do volcanoes erupt?
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Asked by ALOrona to John, Laura, Luke, Rob, Ruth on 10 Jun 2016.
- Robert Williams answered on 10 Jun 2016:
  
  Volcanoes are basically like champagne bottles, when the cork is released the gasses in the wine are out-gassed causing the wine to fountain out of the bottle.
- Laura Finney answered on 10 Jun 2016:
  
  I think what Robert said is probably a good analogy but the truth is I don’t know the details 🙁 It is definitely to do with heat and pressure though!
- Luke Williams answered on 12 Jun 2016:
  
  Champagne is a great example!
  
  Volcanoes are effectively weak spots in the surface of the Earth, caused by the movement of tectonic plates, essentially large areas of the surface. When two pull in different directions, the area between weakens, allowing hot material from the Earth’s core to flood to the surface, sometimes explosively! This can also happen when two plates hit into each other as well.
  
  Eruptions don’t just have to be massive explosions, they can be continuous leaking. It might just be gas and steam, ash or lava, or all three. There are many different types of volcano and they all have different lifecycles.
  
  My favourite is Yellowstone Park in the USA – it is classed as a supervolcano because it is so large.

Question: Why do volcanoes erupt?