Volcanism. Volcanism. Volcanoes are fueled by magma. Once magma forms, it rises towards Earth’s surface because it is less dense than the surrounding mantle and crust. Volcanism describes all the processes associated with the discharge of magma, hot fluids, and gases.
Often, the activity of a volcano depends on the composition of the magma within it.
Temperature – Most rocks begin to melt at temperatures between 800 -1200 degrees Celsius. Temperature increases with depth.
Pressure – Pressure also increases with depth. As pressure increases, the temperature required to melt a rock also increases. This effect of pressure explains why most of the rocks in the lower crust and upper mantle do not melt.ERUPTIONS