Figure 9.17The topography of Mars shows a large range of elevation. (a) Olympus Mons is the tallest volcano in the solar system, with a summit almost 25 km above the surrounding plains. Encircling the volcano is an outward-facing scarp 550 km in diameter and several kilometers high. Beyond the scarp is a moat filled with lava, most likely derived from Olympus Mons. (b) Vallis Marineris is the longest (4000 km) and deepest (up to 10 km) canyon in the solar system. It is five times deeper than the Grand Canyon. In this image, the canyon is exposed as a series of fault-bounded basins whose sides have partly collapsed (as at upper left), leaving piles of rock debris. The walls of the canyon are 6 km high here. The layering of the canyon walls suggests deposition of sedimentary or volcanic rocks prior to faulting.