High gas pressure in magma typically leads to which eruption style?

• A. Less explosive eruption
• B. More explosive eruption
• C. No eruption
• D. Slow lava flow

Answer: (B)

Gas pressure in magma is a key factor in how violently a volcano erupts. As magma rises and the surrounding pressure drops, dissolved gases—primarily water vapor and CO2—come out of solution and form bubbles. If the magma is quite viscous, these bubbles can’t escape easily, so the gas builds up pressure inside the magma. When that pressure becomes too great, the magma fractures and erupts explosively, ejecting ash clouds, pumice, and other tephra in a violent outburst. In contrast, magma that is less viscous or has lower gas content can release the gas more gradually, leading to lava flowing out rather than exploding. So, high gas pressure in magma is associated with more explosive eruptions.