Amy Ferrick, Vashan Wright , Michael Manga, Nicholas Sitar

The orientation of and contacts between grains of sand reflect the processes that deposit the sands. Grain orientation and contact geometry also influence mechanical properties. Quantifying and understanding sand microstructure thus provide an opportunity to understand depositional processes better and connect microstructure and macroscopic properties. We compare naturally-deposited beach sands with laboratory sands created by pouring grains into a container (a process called pluviation). We find that naturally-deposited sands have a narrower distribution of coordination number (i.e., the number of touching grains) and a broader distribution of grain orientations than pluviated sands. We explain the differences through particle rearrangement by flowing water on beaches, which repositions and reorients grains that initially had unstable configurations