• Question: Are there rocks that can explode under pressure?

    Asked by kungfoochicken98 to Debbie, Glyn, Jon, Kat, Nicola on 11 Mar 2013.
    • Photo: Jonathan Stone

      Jonathan Stone answered on 11 Mar 2013:

      This is a really interesting question. Normally if something is under pressure (from the outside) then that pressure stops it exploding. Deep in the earth, where the pressure is really high (because of lots of rock squeezing down), lots of gasses are stored in magma. As the magma gets closer to the surface before erupting as lava, there is less pressure (less rock squeezing it), and the gasses are sometimes able to break the rocks – meaning that the gas escapes. This is like a fizzy drink bottle when you unscrew the lid. Unscrewing the lid releases some pressure, so the gas comes out and the bottle ‘explodes’ or froths over.

    • Photo: Glyn Barrett

      Glyn Barrett answered on 11 Mar 2013:

      When I was in Thailand a few years ago camping next to a river I wanted to make a firepit and surround it with rocks I had taken out of the river. I was told that it wasnt a good idea as they might explode! This is because the rocks can sometimes be porous and have loads of tiny holes in them and when the water gets in them and heats up this causes steam to come out from the rocks and they explode.
      So of course I thought this was really interesting and tried it out for myself. The rocks didnt really explode but a few cracked! So I guess part way there.

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