Mariner 4 Image of the Central caldera of Olympus Mons on Mars

Mariner 9 image of the central caldera of the Martian volcano, Olympus Mons. the basic morphology is similar to terrestrial calderas, although the scale is much larger. The smallest (and youngest) collapse pit, at right, is 30 km across. Concentric fractures and terraces are visible in the larger parts of the caldera. The caldera is about 29 km above the mean Martian surface. North is at 7:00.