Question: Does the composition of volcanic rock change drastically as it makes its ascent towards the surface?

  1. good question!

    generally the composition of a rock is decided when the magma is forming underground. It is dependent on what is melting in order to create your magma. Once the magma has been created it generally won’t change dramatically. But, if the magma is stuck in the ground for a long time before it erupts, then two things can happen….

    1. the heat from the magma can make the surrounding rocks melt. If this happens then you are adding new material into your magma and this will change the composition.

    2. if magma is stuck for a long time, it will start to cool down. As it cools, some minerals which have melted into the magma will start for become solid again. When the crystals are solid they are heavier than the liquid and will move by gravity to the bottom of the liquid. By taking these minerals out of the magma, this also changes the composition!

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