Which magma properties are most associated with explosive eruptions?

Which magma properties are most associated with explosive eruptions?

• A. Gas content only
• B. Silica content only
• C. High gas content and high silica content
• D. None of the above

Answer: (C)

Explosive eruptions are driven by magma that is both viscous and gas-rich. Silica content largely controls viscosity: magma with high silica is thick and resists flow, so gases cannot escape easily. When magma ascends and the pressure drops, dissolved volatiles (like water and CO2) exsolve into bubbles. In a viscous melt, those bubbles get trapped and the internal pressure builds rapidly until the magma fragments and erupts violently. Having both high silica and high gas content makes explosions most likely because the magma is sticky enough to trap gas while there is plenty of gas to drive explosive fragmentation. If gas content is high but the magma is not very viscous, gases can escape and eruptions tend to be effusive rather than explosive. If the magma is highly viscous but gas-poor, it remains sticky but lacks the buoyant, pressurized gas to produce a powerful eruption.

Explosive eruptions are driven by magma that is both viscous and gas-rich. Silica content largely controls viscosity: magma with high silica is thick and resists flow, so gases cannot escape easily. When magma ascends and the pressure drops, dissolved volatiles (like water and CO2) exsolve into bubbles. In a viscous melt, those bubbles get trapped and the internal pressure builds rapidly until the magma fragments and erupts violently. Having both high silica and high gas content makes explosions most likely because the magma is sticky enough to trap gas while there is plenty of gas to drive explosive fragmentation. If gas content is high but the magma is not very viscous, gases can escape and eruptions tend to be effusive rather than explosive. If the magma is highly viscous but gas-poor, it remains sticky but lacks the buoyant, pressurized gas to produce a powerful eruption.