Which factor makes magma less viscous?

Which factor makes magma less viscous?

• A. More silica in magma
• B. Lower temperature
• C. Higher gas content
• D. Less silica in magma

Answer: (D)

Viscosity in magma is driven by how much silica is in the melt. Silica-rich magma forms long polymer chains of silica-oxygen bonds, making the melt thick and resistant to flow. When there is less silica, there are fewer bonds and the melt is less polymerized, so it flows more easily and has lower viscosity. So, the factor that makes magma less viscous is having less silica in the melt. The other factors don’t reduce viscosity in the same way: more silica increases viscosity; cooling (lower temperature) makes magma thicker; and gas content affects eruption behavior but isn’t the primary driver for decreasing viscosity like reducing silica is.

Viscosity in magma is driven by how much silica is in the melt. Silica-rich magma forms long polymer chains of silica-oxygen bonds, making the melt thick and resistant to flow. When there is less silica, there are fewer bonds and the melt is less polymerized, so it flows more easily and has lower viscosity. So, the factor that makes magma less viscous is having less silica in the melt. The other factors don’t reduce viscosity in the same way: more silica increases viscosity; cooling (lower temperature) makes magma thicker; and gas content affects eruption behavior but isn’t the primary driver for decreasing viscosity like reducing silica is.