The process of eruption of volcanoes is summarized into three phases: magma formation and nitial ascent stage, magma chamber stage and stage of exiting from magma chamber to surface.
In the first phase, the formation must have two processes: partial melting and seperation of mother rock and molten mass. In fact, the two processes are unlikely to be independent of each other because the seperation of melting and molten mass may occur before melting. Partial melting is coexistence of liquid (i.e. magma) and solids (crystallization). When temperature rises and press drops and solid phase line decreases. Partial melting may happen. When partial molten mass rises along the mantle flow, the seperation of liquid and solid will occur, resulting in the movement of the liquid and even aggregation, which is called the liquation.
In the second phase, the magma pocket is the area under the volcano that fills the magma, where the magma is relatively concentrated in the earth’s crust or upper mantle rock. It is generally regarded as fluid of high temperature which is similar to oil deposit in a rock pore (or crack). Generally, lava accounts for 5%-30% of total volume in mantle plume. Locally, it can be considered as a liquid set of relative internal circulation. Magma is mixture of magma melt, volatiles and crystals.
In the third phase, magma rises from the magmatic source region to near surface, which is related to the excess pressure of magma chamber, the formation of channels and the crystallization and degassing process of the magma rising. When tension or shear stress in the crust is greater than the local strength of rock failure, extensional or single shear fracure may form consequently. If these fractures connected one another, it can be a channel of magma eruption.
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