Summary
Highlights
A volcano is a vent or 'chimney' that connects magma from within the Earth’s crust to the Earth's surface. The liquid rock is called magma when it's underground and lava after it comes out.
Molten rock in the magma chamber rises through the crater pipe. As it moves up the main vent, gases expand and water turns to steam, building pressure. When the pressure becomes too great, the volcano erupts through the crater and secondary side vents.
Common gases released by volcanoes include water vapor, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen fluoride, and hydrogen sulfide.
Volcanoes aren't just cone-shaped mountains; they can also be wide plateaus, fissure vents, and bulging dome shapes. Some are found on the ocean floor and even under icecaps, like those in Iceland.
The word 'volcano' comes from 'Vulcan,' the Roman god of fire. The tallest volcano in the Solar System is on Mars, not Earth.