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Volcanic eruptions occur when magma in the Earth’s mantle forces its way through holes or cracks in the crust. Once magma has been erupted from a volcano it is called a lava flow. Lava is very hot, up to 1200 °C.  When the lava is at the surface it begins to cool as it flows. As lava cools, it begins to change from a runny liquid to a more sticky mix of liquid lava and solid rocks and crystals. As the lava continues to cool, small crystals will grow and form lumps of solid rock which are carried by the lava. Once fully cooled and solidified rock will be left behind.


Suitable for ages 5+ with adult supervision.

Activity Information

In this activity you will investigate how the growth of crystals and rock in lava affects how it flows. Golden syrup will represent the liquid lava, sprinkles represent small crystals and marshmallows represent blocks of rock. The aim of this experiment is to find out if lava flows slower or faster when crystals and rock have started to form in it.


  • water
  • yogurt
  • golden syrup
  • marshmallows
  • sprinkles
  • cups or similar
  • drinking straws


Download the activity booklet from the Earth and Solar Systems website.

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