These channels resemble arroyos, which are channels in which water flows through occasionally, located in the United States. These arroyos need extenisive running water for their formation, thus implicating that Mars once had a period of flowing water. These two hemispheres have different characteristics. The southern hemisphere is relatively flat, older and heavily cratered. The northern hemisphere is much younger and has extensive lava flows, collapsed depressions and huge volcanoes.
Shield volcanoes are perhaps the most awesome Martian feature.
The largest volcano is Olympus Mons which is about 600 km. It is approximately 2.5 times the height of Mt. Everest. The enormous mass of Olympus Mons requires that the Martian crust beneath it be thicker than under such smaller volcanoes on earth. The Valles Marineris, which is a giant canyon dividing the northern and southern hemispheres, is the only sign of local tectonics. Mars' planetary history is thought to have followed a planetary sequence similar to that of earth's.