Cross bedding formation:
-A current (blue arrow) moves sand up (black arrows) over a ripple or dune, and when it reaches the crest, the sand falls down the slip face.
-The slip face tends to be a zone of fairly low energy, sort of like an eddy zone in a river. Here, material can be deposited, as it is more or less “shielded” from the current by the dune.
-As the current continues to move sand over the dune/ripple, more cross beds are formed, but all the while the back of the dune/ripple is eroding.
-The 34° shown is the angle of repose of the sand—the maximum angle which sand while pile up before toppling over.
