The Letter A
The letter A represents a magma chamber. Magma is molten rock that is located under the surface of the Earth. A magma chamber is usually located far beneath the surface of the Earth where an oceanic plate is driven down into the mantle by a continental plate. The oceanic plate melts as it desends into the upper layer of the mantle. Some ocean water gets trapped with the oceanic plate and is turned into steam by the intense heat.
The magma is less dense and under extreme pressures that force it up toward the surface. This molten rock and gas collects in a magma chamber until it can escape to the surface.
Click on the "Next" icon to learn about one passageway that magma uses to reach the surface.