What happens to make a volcano erupt?

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Magma rises through cracks or weaknesses in the Earth's crust. When this pressure is released,  as a result of plate movement, magma explodes to the surface causing a volcanic eruption. The lava from the eruption cools to form new crust. Over time, after several eruptions, the rock builds up and a volcano forms.

Magma rises through cracks or weaknesses in the Earth's crust. When this pressure is released, as a result of plate movement magma explodes to the surface causing a volcanic eruption.