The martian atmosphere is composed of 95.3 percent carbon dioxide, 2.7 percent nitrogen and 1.6 percent argon. This would be sufficient to suffocate a human in a matter of minutes. The atmospheric pressure there is about 1 percent that of Earth's. Dust storms occur frequently on Mars. These can be local, regional or can cover the entire planet.
Dust can reach as high as six miles above the surface and settles very slowly.
The highest point on Mars is the Olympus Mons, a large shield volcano about 16 miles high and 370 miles across. This surface feature covers about the same area as the state of Arizona. The martian canyon system of Valles Marineris is the largest and deepest in the solar system. It runs more than 2,500 miles and has plateaus that extend upward from the canyons to altitudes of three to six miles. These are believed to be large channels cut by ancient rivers.