Popular volcanic mountain names are Mount St. Helens in the United States mainland, Mauna Loa in Hawaii, Mount Rainier in Washington, Mount Edziza in British Columbia and Hoodoo Mountain in Canada. Many of the highest volcanoes are located in Chile and Argentina, such as Ojos del Salado, Tacora, Tromen, Copahue and Risco Plateado.
Earth is not the only planet with volcanoes. The planet Venus has too many volcanoes to name. Planetary bodies like Mercury and the Moon have volcanoes that have not been active for billions of years. Several satellites of the giant planets Jupiter and Saturn have volcanoes. The largest volcano in the Solar System is Olympus Mons on the planet Mars. It stands three times higher than the tallest mountain on Earth.
Volcanoes form when liquid rock from the Earth's mantle wells up and explodes in a shower of gas and lava. Over geological timescales, this lava solidifies and builds up to ever-increasing heights. Every time the pent-up gases in the mantle become too much, the rock melts and wells up to the surface in another explosion. On Earth, the sizes of volcanoes are limited by plate tectonics. On Mars, which has no moving continental plates, a volcano like Olympus Mons just keeps growing taller.