What is the effect of silica content on magma movement?

• A. The more silica there is the faster the movement
• B. Silica content has no effect on movement
• C. The more silica there is the slower the movement
• D. The more silica there is the hotter the magma becomes

Answer: (C)

Silica content controls how viscous magma is. When there’s more silica, the silicate network in the melt becomes more polymerized, making the magma thicker and stickier. A higher-viscosity magma resists flow, so it moves more slowly through vents and magma chambers. That’s why silica-rich magmas (like rhyolite and andesite) tend to rise and erupt more explosively or ooze out slowly, but not flow swiftly, while silica-poor magmas (like basalt) flow more readily. So, increasing silica leads to slower magma movement, which is why this option is the best choice.