Learn about Olympus Mons

large shield volcano on the planet Mars centred at 19N, 133W. Possibly the largest volcano in the entire solar system, Olympus Mons consists of a central edifice 27 km (88,600 feet) high and 540 km (335 miles) across that is surrounded by an outward-facing cliff up to about 10 km (32,800 feet) high. At the summit is an 85-km- (53-mile-) diameter crater or caldera. For comparison, the largest volcano on the Earth, Mauna Loa, Hawaii, measures 120 km (74 miles) across and reaches a height of 9 km (5.5 miles) above the ocean floor. The low slopes of its flanks and the presence of numerous long flows and lava channels suggest that Olympus Mons consists largely of relatively fluid basaltic lava. Its tremendous size has been attributed to the stability of the Martian crust and to a long accumulation time, possibly in excess of one billion years.