In Google Earth we can see some very clear lines in the Sahara. In the screenshot below you can clearly see these lines starting at the top going southward, then gently curving westward towards the bottom.
What are these structures and how were they formed? Are they related to the wind? Some sort of flow? Are they surface structures or they are embedded deep in the rock? Or something else?
I realize that this may be a trivial question for anyone with some knowledge of geology, but I really wasn't able to google up the answer.