What is Olympus Mons?

The tallest mountain and the largest volcano in the solar system

Mars has many interesting features, but none so striking as Olympus Mons. Astronomers believe the mountain formed fairly recently in the planet’s geologic history, with the ‘youngest’ areas around 2 million years old. This shield volcano has a shallow slope and is wider than it is tall. It formed from very low viscosity lava that flowed over a long period of time. The peak of Olympus Mons contains a large caldera, a cavity that formed when the roof of the volcano’s magma chamber collapsed and the ground above collapsed into it.

More lava activity caused additional, smaller calderas that overlap the larger one, creating a caldera complex. The volcano also has two named craters; the Karzok Crater is 15.6 kilometres wide and the Pangboche Crater is 10.4 kilometres wide. Olympus Mons lies in Tharsis, a bulging volcanic region on Mars. The area is also home to three smaller volcanoes known as the Tharsis Montes.

Olympic-sized mountain

Rising more than 27 kilometres above the surface, Olympus Mons is three times the height of Earth’s tallest mountain, Mount Everest. It is about 550 kilometres wide, surrounded at its edges by escarpments called Olympus Rupes that are about six kilometres high. If a person were to stand on the surface of Mars, they would not be able to see the top of Olympus Mons due to its height, size and shallow slope. 

Olympus Mons likely grew to such an impressive height due to Mars’s lack of plate tectonics. Without a shifting crust, lava piled up in one place. Mars’s low surface gravity, only about 40 per cent that of Earth’s, also accounts for the long lava flows that made Olympus Mons so wide.


 This article was originally published in How It Works issue 10


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