A view across the summit of Mauna Loa. The caldera is about .9 miles (1.5 kilometers) across. The summit of Olympus Mons on Mars probably looks similar but its caldera is 56 miles (90 kilometers) across. Olympus Mons is the largest volcano in the solar system. The volcano is 17 miles (27 kilometers) high and covers an area the size of the state of Arizona on the Tharsis Plateau.