Olympus Mons is the tallest mountain in the solar system, rising about 21.9 kilometres on Mars.
Olympus Mons is a gigantic shield volcano in Mars’s Tharsis region. Its exceptionally broad, gently sloping profile was built by repeated eruptions of fluid basaltic lava. Unlike a steep terrestrial stratovolcano, it spreads across a vast area, making its size easier to underestimate in ordinary images.
The mountain rises roughly 21.9 kilometres above the Martian reference level and is about two and a half times the height of Mount Everest above sea level. Its summit contains a complex group of overlapping calderas formed as the magma chamber emptied and the summit collapsed in stages.
Olympus Mons is not currently known to be erupting. Mars has much less surface recycling than Earth, allowing ancient volcanic edifices to grow enormous and remain preserved for billions of years.