Which combination of magma characteristics would most likely lead to a more explosive eruption?

• A. Higher temperatures and more gas content
• B. More silica content and higher temperatures
• C. Less silica content and higher temperatures
• D. More gas content and more silica content

Answer: (D)

Explosive eruptions are driven by magma that is both viscous and gas-rich. Silica-rich magmas are highly viscous because their structure traps crystals and bubbles, so gases stay dissolved and can’t escape easily. When pressure drops as magma rises, those dissolved gases exsolve and bubble growth builds until the magma fractures violently. If there’s a lot of dissolved gas present, the internal pressure is even higher, producing a more powerful explosion with ash clouds and fragmented rock.

So the combination of more silica content and more gas content creates the conditions for the strongest, most explosive eruptions. Higher temperature tends to lower viscosity, which would allow gases to escape more readily, making eruptions less explosive even if gas content is high. Low silica content lowers viscosity, also reducing explosive potential because gases can escape more easily.