Olympus Mons (Latin, "Mount Olympus") is the tallest known mountain in our solar system, located on the planet Mars.
The central ediface stands 27 kilometres (88,600 feet) high over its base (over three times the height of Mount Everest); it reaches 25 kilometres above the mean surface level of Mars, since it stands in a two-kilometre-deep depression. It is 540 km (335 miles) in width, flanked by steep cliffs, and has a caldera that is 85 km (53 miles) long, 60 km (37 miles) wide, and up to 3 km (1.8 miles) deep with six overlapping pit craters. Its outer edge is defined by an escarpment up to 6 km (3.7 miles) tall unique among the shield volcanoes of Mars.
Olympus Mons is an apparently extinct shield volcano, the result of highly fluid magma flowing out of volcanic vents over a long period of time, and is much wider than it is tall; the average slope of Olympus Mons' flanks is very gradual.
The volcano is surrounded by a region known as the Olympus Mons Aureole (Latin, "Circle of Light") with gigantic ridges and blocks extending 1000km (621 miles) from the summit that show evidence of development and resurfacing connected with glacial activity. Both the escarpment and the Aureole are poorly understood. In one theory this basal cliff was formed by landslides and the Aureole consists of material piled up at the bottom of these landslides.
The Hawaiian islands are an example of similar shield volcanoes on a smaller scale; see Mauna Loa. The size of this volcano is likely due to the fact that Mars does not have tectonic plates. Thus, the crust stayed on top of that hot spot and continued to discharge lava, bringing it to such a height.
Olympus Mons is located in the Tharsis bulge, a huge swelling in the Martian surface that bears numerous other large volcanic features. Among them are a chain of lesser shield volcanoes including Arsia Mons, Pavonis Mons and Ascraeus Mons, which are small only in comparison to Olympus Mons itself. The land immediately surrounding Olympus Mons is a depression in the bulge 2km deep.
In the days before space probes revealed its identity as a mountain, Olympus Mons was known to astronomers as the albedo feature Nix Olympica.
Olympus Mons is located at approximately 133°W by 18°N.