• Question: why do volcanoes erupt??

    Asked by poppxx to Mike, Pip, Tianfu, Tim, Tom on 26 Jun 2012.
    • Photo: Tom Lister

      Tom Lister answered on 26 Jun 2012:

      I’m guessing here: that the magma formed below the surface must increase in volume or the chamber must get smaller.
      In the first case: Either it gets hotter for some reason and more rocks melt (the magma is less dense and so would expand), or some magma starts flowing into the chamber from somewhere else.
      In the second case: perhaps this is due to the movement of tectonic plates?

    • Photo: Tim Stephens

      Tim Stephens answered on 26 Jun 2012:

      It’s related to changes in pressure in the ground underneath the volcano. The molten rock in the core of the earth is always bubbling and moving (slowly) and sometimes the pressure gets so high that it pushes through a weak spot in the earth’s crust. As it does so, it is not being squashed so hard and gets runnier and able to squeeze through cracks in the rocks and erupt.

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