Temperature

When parts of the plate melt, the magma rises over the volcano, therefore the higher the temperature the more amount of magma is produced. Depending on their composition, the majority of rocks begin to melt at temperatures between 800 and 1200 degrees. Additionally, the temperature, pressure, and water also affect the formation of the magma. For example, high temperature keeps magma movable and the viscosity of the magma.

 

As pressure increases, the temperature at which a substance melts also increases, which explans why most of the rocks in Earth's lower crust and upper mantle do not melt.