Question: what is the relationship between magma viscosity and volcano shape?
Answer: On the other hand, when more viscous (higher viscosity) lavas do erupt, they usually do so explosively. Viscosity also affects the shapes of lava flows and the mountains they erupt from. The more viscous the magma, the fatter the lava flow. Also, the more viscous the magmas a volcano erupts, the steeper the volcano.