Here's why:

* Volcanoes are formed by the accumulation of lava, ash, and other volcanic materials erupted from a vent in the Earth's crust.

* Magma is molten rock found beneath the Earth's surface. When magma reaches the surface, it's called lava.

* The eruption of lava and other volcanic materials creates the characteristic cone-shaped or dome-shaped structure of a volcano.

Let me know if you have any other questions!