How does the mineralogical composition of magma, particularly its silica content, influence the type of

Question

How does the mineralogical composition of magma, particularly its silica content, influence the type of material erupted byu a volcano and the nature of the eruption in general?

Answer 1

The more silica in the magma, the thicker it is and generally, the bigger the eruption when it blows.

Gas trying to escape a magma  that's high in silica has a harder time reaching the surface because it is more viscous (thicker) and when it does tends to cause more massive eruptions

Volcanoes with magma  low in silica erupt more often, but the magma is thinner and flows more freely, and the eruptions tend to be smaler

Answer 2

The composition of the magma effects its viscosity.

I think it goes that if it is silica rich it is viscous and mafic-mineral rich is fluid. So the silica rich magma should explode and the mafic stuff should flow easily (e.g. like Hawaii) - but I am probably oversimplifying

ADDED: In fact water dissolved in the magma has a huge effect on the viscosity too!