Olympus Mons on Mars: The Largest Volcano.

The largest volcano in the Solar System is on Mars. Olympus Mons rises 24 kilometers high and measures 550 km across. By comparison, Earth' s largest volcano, Mauna Loa in Hawaii , rises 9 km high and measures 120 km across. Such large volcanoes can exist on Mars because of the low gravity and lack of surface tectonic motion. Olympus Mons is a shield volcano , built by fluid lava. Over the next three years, Mars Global Surveyor , which arrived at Mars last week, will photograph the planet at such high resolution that objects only 100 meters across will be visible. The above image was taken by Mariner 9 , which orbited and photographed Mars during 1971 and 1972.