Video narration
How can a mountain grow from deep inside Earth? Think of a shaken fizzy drink bottle: pressure escapes through an opening. A volcano is very different, but shares that one clue. Far below, some rock melts. Underground molten rock is called magma. It rises through cracks in Earth's crust as pressure pushes upward. Volcanoes form in different places, including near plate edges or above hot spots. When magma reaches the surface, it becomes lava. Eruptions send lava, ash, and broken rock out; these gather around the opening, layer by layer. But a volcano is not usually a mountain that simply splits open. Eruptions build it up. Repeated eruptions can make steep cones, broad low volcanoes, or formations along long cracks. That is how a volcano grows from deep inside Earth: molten rock rises through the crust, erupts, and gradually builds up around an opening.