What Controls the Shape of Dunes?
ES1603  Types of Dunes

If all the "ingredients" for dune formation are available in the same place at the same time, dunes can form. In general, the type of dunes that form depends on the abundance of the sediment supply and the variability of the wind direction.

  !   Examine the images and captions to see the types of dunes that form under different conditions.

John McCauley, USGS
Barchan dunes on beach in Peru. Barchan dunes form in areas of limited sand supply where the wind blows from just one direction. Wind is from the right to left in this image.
Longitudinal dunes in Egypt as viewed from Earth orbit. These long, straight dunes are parallel to the wind direction. They form in areas where the sand supply is moderate and winds usually blow from the same general direction.
John McCauley, USGS
Airphoto of a parabolic sand dune. Parabolic dunes can form when vegetation begins growing on the ends of a sand dune, holding them in place while the rest of the dune moves ahead. Parabolic dunes can form where sand supply is moderate and wind is from a single direction.
Peter Kresan, University of Arizona
Airphoto of transverse dunes in Algodones, California. Wind direction is from right to left across the image. Transverse dunes form where sediment supply is abundant and the wind blows in the same general direction.

7. In the boxes, sketch each dune type and indicate the wind dynamics and sand supply required to form each dune.

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