how does a volcano erupt?

Question

askNib · Accepted Answer

Deep underground, rock gets so hot it melts into magma — molten rock lighter than the solid rock around it. Because it's lighter, magma rises, forcing its way up through cracks in the crust toward the surface. Trapped inside the rising magma are dissolved gases — like water vapor and carbon dioxide — squeezed under huge pressure. As magma nears the surface, pressure drops suddenly — the gases burst out of solution, like shaking a soda bottle and popping the cap. That expanding gas blasts magma, ash, and rock skyward — an eruption — building the classic volcano cone we all recognize. So a volcano erupts because rising magma loses pressure, and its trapped gas explodes outward, carrying molten rock with it.