Question: what are the three main components of magma what factors control and how the viscosity of magma?
Answer: Magma Composition: Silicate-rich magmas are typically formed at destructive plate boundaries, by partial melting and/or assimilation of crustal rocks (which are richer in silica than the rock of the mantle). ... 
Temperature: ... 
Volatile Content: ... 
Crystal Content: ... 
Experiements.