Mounds or ridges of sand which are asymmetrical and are produced subaqueously by flowing water. The external morphology is similar to the smaller ‘ripple’ and larger *‘sand wave’, with a gently sloping, upstream side (stoss), and a steeper downstream side (lee). The crestline elongation extends transverse to the flow direction and is sinuous or lunate in plan. The height varies between 0.1 m and 2 m, while the wavelength (spacing) between dunes is 1–10 m. Size and growth are limited by water depth and, in general, dune height is less than one-sixth of the flow depth. The down-current migration of dune bedforms leads to the formation of cross-bedding in sediments.
Subjects: Ecology and Conservation — Earth Sciences and Geography.