The main reason for the eruptions from volcanoes is the heat deep within the Earth's mantle. This heat slowly melts rocks to create a slow moving substance called magma. Magma is lighter than the solid rock around it so magma rises and collects in magma chambers. After a while the magma pushes through vents and fissures in the earth's surface. Then a volcanic eruption occurs! The magma comes out of the volcano and is now called lava.
These pictures show how the lava comes up and out of the volcano.
Now, as all of the magma has risen to the surface of the
volcano, it explodes and trickles down the side of the mountain.
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