Mars has several large volcanoes on its surface. Although the volcanoes are not erupting as of 2011, they do demonstrate Mars once experienced a great deal of volcanic activity. Two of the planet's volcanoes, Olympus Mons and Ascraeus Mons, are 16 miles above the average Martian surface elevation; this is about 2 1/2 times the height of earth's Mount Everest. Olympus Mons is a shield volcano that stretches 600 km across its base. In comparison, the earth volcano Mauna Loa is only about 200 km across its base and is the earth's largest shield volcano.
Mars has several canyon systems, which include Valles Marineris, which is 5,000 km long, as wide as 500 km and as deep as 6 km. This system was formed by the faulting of the planet's crust. The Candor Chasma system was also formed by the faulting of the crust but also by volcanic activity and ponds of water.
Mars has several craters including the Argyre Basin, which is surrounded by a ring of mountains that rises approximately three miles above the basin floor. Some Martian craters are the result of meteorite impact, and their particular formation provides evidence to the past presence of water on Mars; crater rims have been smoothed out by running water erosion, and young Martian craters exhibit patterns that indicate water or ice under the surface.
Several of the surface features of the planet lead scientists to believe that running water was once present. On May 28, 2002, scientists discovered ice-rich soil beneath the Martian surface. Some craters have a shape that indicates they were created by an impact, such as from a meteorite, that landed in mud. Stream channels on Mars are also evidence of a past area of water on the surface.