Aeolian accumulations
445
Transverse dune
Seasonal reversal
of crest line
Reversing dune
with incipient
star dune arm
Development of arm
by secondary flow
Accentuation of
arms by third wind
direction and secondary
flow
Figure 18.18. Model for the formation of pyramidal dunes (star dunes) by the development of secondary
wind flows, while the dune is mobilized in a multidirectional wind regime Modified from Lancaster,
1989b.
varieties of the sand sheets (Breed and Grow, 1979). The surfaces can be irregular,
undulated with or without ripples, and so forth. Many sand sheets are the basis or support
of other mobile dunes. Globally, the extent of the sand sheets is more than one and a half
million km 2 and, at the beginning of this chapter we have pointed out that the maximum
surface known is ---100,000 km 2, in the borders between Egypt, Sudan, and Libya.
445
Transverse dune
Seasonal reversal
of crest line
Reversing dune
with incipient
star dune arm
Development of arm
by secondary flow
Accentuation of
arms by third wind
direction and secondary
flow
Figure 18.18. Model for the formation of pyramidal dunes (star dunes) by the development of secondary
wind flows, while the dune is mobilized in a multidirectional wind regime Modified from Lancaster,
1989b.
varieties of the sand sheets (Breed and Grow, 1979). The surfaces can be irregular,
undulated with or without ripples, and so forth. Many sand sheets are the basis or support
of other mobile dunes. Globally, the extent of the sand sheets is more than one and a half
million km 2 and, at the beginning of this chapter we have pointed out that the maximum
surface known is ---100,000 km 2, in the borders between Egypt, Sudan, and Libya.