There are many craters on Mars. Some of them bigger than the Grand Canyon. One of the largest systems of canyons on Mars is called Valles Marineris. This canyon system is 4,000 km long and is 2-7 km deep. Mars also has the largest mountain in the solar system. It rises 24 km (78,000 ft) over the surrounding plain. Its base is over 500 km in diameter. Mars also has many volcanoes. Some of the largest volcanoes on Mars are : Ascraeus Mons , Pavonis Mons , and Arsia Mons. Some of these volcanoes are 6 km high. Scienticts are pretty sure the volcanoes were once active because they have found ridge like lava flows near the volcanoes. They are pretty sure theese volcanoes will not erupt again , because like the moon, Mars is lacking in techtonic plates. This means that because there are so few plates they will most likely not collide to create natural disasters such as earthquakes and volcanoes errupting.