This image shows the rock Yogi and tracks from the Rover. Click on image for full size version (40K GIF) Image from: JPL/NASA

Unlike the rocks of Earth, where there are many things which cause erosion, there are only two main weathering agents on Mars: wind and acid fog. Acid fog is very important, but because there is not a lot of water, the action of sand and wind is the most important thing to cause changes to the planet's surface.

Wind erosion of Mars was examined in the Mars Pathfinder mission. Rocks examined by the Pathfinder's Rover found evidence of the following erosion features:

• wind tails
• ripples
• sand dunes on the surface
• pits and holes in the rocks

Sand and dust from the surface is whipped up by the winds of Mars and distributed around the globe in global dust storms. The force of winds during these storms pounds sand into the rock formations, contributing toward the breakdown and recycling of the Martian surface.