Sunrise over the largest mountain in the solar system. Olympus Mons, located in the western hemisphere of Mars, is a massive shield volcano that is approx. 25 km (16 mi) high, making it nearly three times as tall as Mount Everest (the tallest mountain on planet Earth).
Also, the massive diameter of 624 kilometers (374 miles) makes the volcano about the same size as the state of Arizona.
The extraordinary size of Olympus Mons is likely because Mars lacks mobile tectonic plates. On Earth, we have tectonic plates that essentially slide around on a mechanically weak subsurface layer known as the asthenosphere.
A combination of sea-floor spreading ridges and plate subduction keeps the plates of Earth consistently moving. As a result, when mantle-sourced plumes of molten rock (“hotspots”) rise into the overlying mobile tectonic plate, the associated volcanism at the surface migrates over time (i.e. Hawaii).
During the eruption of Olympus Mons, the crust of Mars remained fixed over a stationary hotspot, and the volcano continuously discharged lava until it reached an enormous height. Olympus Mons has been heavily studied by planetary scientists, and will continue to give us clues to the geologic history of the red planet.
Photo credit: NASA