The explosiveness of a volcanic eruption depends on how many gas bubbles form in the magma—and when. Until now, it was thought that gas bubbles were formed primarily when the ambient pressure dropped ...

One of the most explosive volcanoes in U.S. history began its eruption with a trickle, not a blast. Mount St. Helens' gas-laden magma oozed into the cone before the mountain finally erupted in 1980.

Forbes contributors publish independent expert analyses and insights. David Bressan is a geologist who covers curiosities about Earth. How and if a volcano explodes depends on how and when bubbles of ...