Complex sentence: When a dust devil goes by it blows away the coating and exposes the underlying dark surface, which within a few weeks assumes its former bright colour, either from being re-covered through wind action or some form of oxidation through exposure to sunlight and air.
Split into simpler sentences: 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 air.