What is the effect of silica content on magma movement?

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.

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.