Mantle plume
The magma that erupts from a volcano is formed deep within the Earth's crust and upper mantle. The partial melting of rock generates magma due to the increase in temperature and pressure caused by the upwelling of this hot, buoyant material. As the magma rises toward the surface, it may collect in a magma chamber, where it can continue accumulating and solidifying. When the pressure in the chamber becomes too great, it may force its way to the surface through a vent or fissure, resulting in an eruption.
Molten rock
The magma's source is partially melting rocks in the Earth's upper mantle caused by the heat from the Earth's core. The molten rock mainly consists of silicon, aluminum, oxygen, and iron. As the magma rises, it can collect water vapor, carbon dioxide, and sulfur dioxide, which can escape during an eruption.