4.3 EOLIAN PROCESSES
111
Fig. 4.20. (A) Air photograph of a sand sea composed of seif (longitudinal) dunes aligned parallel to average wind direction. Note the flat interdune areas. (Courtesy of K. Glennie.) (B) Illustration showing the formation of seif (longitudinal) dunes from a helical flow system developed by unidirectional wind flow.
sus of opinion is that they are f o r m e d from helicoidal flow cells set up by unidirectional
wind systems (Fig. 4.20B).
The fourth type of eolian dune is the transverse variety. These are straight, or slightly
sinuous, crested dunes that strike perpendicular to the m e a n wind direction (Figs. 4.19D
111
Fig. 4.20. (A) Air photograph of a sand sea composed of seif (longitudinal) dunes aligned parallel to average wind direction. Note the flat interdune areas. (Courtesy of K. Glennie.) (B) Illustration showing the formation of seif (longitudinal) dunes from a helical flow system developed by unidirectional wind flow.
sus of opinion is that they are f o r m e d from helicoidal flow cells set up by unidirectional
wind systems (Fig. 4.20B).
The fourth type of eolian dune is the transverse variety. These are straight, or slightly
sinuous, crested dunes that strike perpendicular to the m e a n wind direction (Figs. 4.19D