MAGMA FORMATION(MOLTEN MATERIAL BELOW THE SURFACE)

Magma Formation (molten materials below the surface):
Elevated temperatures within the Earth (possibly caused by the decay of nearby radioisotopes) cause the rocks ions to vibrate in their lattice position. Increased heating may eventually collapse the lattice, forming liquid or molten material.
Another cause of temperature elevation is the natural increase in temperature as depth increases. This is known as the geothermal gradient.
As pressure increases, the melting temperature also increases (provided the rocks are dry). Conversely the presence of water or water vapor in the rocks will lower the rock’s melting point. A wet rock will melt at a lower temperature than a dry rock of the same composition.
2. As pressure rises, so do the effects of water, therefore as the pressure on a wet rock increases the temperature at which it melts decreases. This is the exact apposite of dry rock.
At a depth of 35km to 40 km the geothermal gradient is just enough to start melting average crustal rock (in the presence of water) forming magma.
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