1. Temperature: Magma becomes less viscous (thinner and more fluid) as its temperature increases. This is because the increased thermal energy weakens the bonds between the silica tetrahedra, making the magma flow more easily.

2. Silica Content: Magma becomes more viscous (thicker and less fluid) as its silica content increases. This is because silica tetrahedra readily bond with each other, forming long chains and networks that resist flow.

These two factors are the primary drivers of magma viscosity, which in turn influences how magmas erupt and the types of volcanic features they form.