Magma
is less dense because it is a fluid, is hot, and it is full of
gases.Ultimately a volcano is an expression of the lightest minerals in a
magma, mixed with volatile gases. It is true that molten rock takes up
more space than cold rock, because the ions involved are in a greater
state of excitement.
Heat rises, and as it rises it takes with it the molten magma, but as it rises it also loses heat, thereby dropping higher melting point minerals out of solution.If magma is less dense than the surrounding rock it will rise, according to the physical laws of gravity. Magma finds its own level, where it is in density equilibrium with its surrounding rocks. Fractionation can occur within the magma body, where the heavy minerals created will crystallize and sink within the body, and the lighter fluid will rise until it finds another density equilibrium. Magma created in subduction zones generally contains more volatile gases than other knids of magma because a lot of water has been incorporated within the subducting slab as zeolites. This reduces the melting point of the magma.Aso, from a slight;y different perspective, there is an interchange between granite and its surrounding greywacke, both are very similar in density, and in the vicinity of a felsic orogeny bits of granite can be found in greywacke, and bits of greywacke (xenoliths) can be found in granite .
Heat rises, and as it rises it takes with it the molten magma, but as it rises it also loses heat, thereby dropping higher melting point minerals out of solution.If magma is less dense than the surrounding rock it will rise, according to the physical laws of gravity. Magma finds its own level, where it is in density equilibrium with its surrounding rocks. Fractionation can occur within the magma body, where the heavy minerals created will crystallize and sink within the body, and the lighter fluid will rise until it finds another density equilibrium. Magma created in subduction zones generally contains more volatile gases than other knids of magma because a lot of water has been incorporated within the subducting slab as zeolites. This reduces the melting point of the magma.Aso, from a slight;y different perspective, there is an interchange between granite and its surrounding greywacke, both are very similar in density, and in the vicinity of a felsic orogeny bits of granite can be found in greywacke, and bits of greywacke (xenoliths) can be found in granite .
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