Question

write a short note on sand dunes

Answer 1

Sand dune, any accumulation of sand grains shaped into a mound or ridge by the wind under the influence of gravity. Sand dunes are comparable to other forms that appear when a fluid moves over a loose bed, such as subaqueous “dunes” on the beds of rivers and tidal estuaries and sand waves on the continental shelves beneath shallow seas. Dunes are found wherever loose sand is windblown: in deserts, on beaches, and even on some eroded and abandoned farm fields in semiarid regions, such as northwest India and parts of the southwestern United States. Images of Marsreturned by the U.S. Mariner 9 and Viking spacecrafts have shown that dunes are widely distributed on that planet both in craters and in a sand sea surrounding the north polar ice cap.