https://www.youtube.com/watch?v=LMLtS7gAdX8

When magma gushes out of weak spots on the outside of the volcano or out of the top of the volcano, it is called an eruption. An eruption is like opening a can of shaken soda. In a can of soda, bubbles of gas separate from the liquid and force the liquid out, just like the gas and pressure force the magma out of the volcano. When magma erupts from the volcano, it turns into lava.