Many areas on Mars experience the passage of giant dust devils. These dust devils leave tracks on the surface of Mars because they disturb a thin coating of fine bright dust that covers most of the Martian surface. When a dust devil goes by it blows away the coating and exposes the underlying dark surface. Within a few weeks, the dark track assumes its former bright colour, either by being re-covered through wind action or due to surface oxidation through exposure to sunlight and the Martian atmosphere.