Video narration
How can a volcano turn pressure into a blast of rock-and what happens to lava when it erupts under the sea? Think of a shaken fizzy drink: trapped gas pushes liquid toward an opening. In a volcano, melted rock sits in a deep magma chamber. Pressure and gas drive it upward through cracks and a channel to a vent-the opening at the surface. Below ground, it's magma. Once it breaks out, it's lava, while ash and volcanic gases rise. But underwater, lava usually doesn't vanish or race along as a river of fire. Cold seawater chills its outside almost at once. That shell hardens, while hotter lava can still move inside. The result is pillow lava: rounded, solid lobes that pile up on the seafloor. Hot lava meets cold water, cools, hardens, and builds new seafloor beneath it.