how does a volcano erupt?

1magma forms

Deep underground, rock gets so hot it melts into magma — molten rock lighter than the solid rock around it.

2magma rises

Because it's lighter, magma rises, forcing its way up through cracks in the crust toward the surface.

3gas pressure

Trapped inside the rising magma are dissolved gases — like water vapor and carbon dioxide — squeezed under huge pressure.

4pressure drops

As magma nears the surface, pressure drops suddenly — the gases burst out of solution, like shaking a soda bottle and popping the cap.

5the eruption

That expanding gas blasts magma, ash, and rock skyward — an eruption — building the classic volcano cone we all recognize.