1. Cooling:
* Crystallization: As magma cools, minerals start to crystallize out of the molten rock. The type of minerals that form depends on the chemical composition of the magma. This process can change magma from a completely molten state to a mixture of solid crystals and liquid magma.
* Solidification: If the magma cools enough, it will solidify completely, forming igneous rock.
2. Pressure Changes:
* Decompression Melting: When pressure on magma decreases (e.g., due to plate tectonics), it can cause melting, creating more magma. This is how magma is generated at mid-ocean ridges and volcanic arcs.
* Pressure-induced Crystallization: Conversely, increasing pressure can cause some minerals to crystallize out of magma, changing its composition.
3. Chemical Reactions:
* Assimilation: Magma can melt and incorporate surrounding rock, changing its chemical composition and potentially forming new minerals.
* Fractional Crystallization: As magma cools, different minerals crystallize at different temperatures. If the crystals are removed from the magma, it can change its chemical composition and become more enriched in certain elements.
4. Water Content:
* Volatiles: Water and other volatiles (gases) can dissolve in magma. As the magma rises and pressure decreases, these volatiles can be released, potentially causing eruptions.
* Viscosity: The presence of volatiles can affect the viscosity of magma, making it more fluid and potentially more explosive.
In summary: Magma is a dynamic system, and its form can change due to cooling, pressure variations, chemical reactions, and the presence of volatiles.
