Basic Types of Dunes - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 78

Fig. 6.13 Barchans on Mars merging to form gentle barchanoid ridges. HiRISE image ESP_014404_1765. The slip faces indicate that these
barchans are moving towards upper right, and hence colliding with the larger sand mass and barchanoid ridges. Image NASA/JPL/U.Arizona

exposed to occasionally-reversed winds tend to have an
open 'wing' shape and may have crests with slip faces in
both directions (Fig. 6.25 ). Recent comparisons of the
profiles of reversing dunes on Earth to TARs on Mars
suggest that a reversing dune origin seems likely for large
TARs (Zimbelman 2010).

6.7 Star

Dunes with three or more slip faces are the result of sand-
driving winds from multiple directions. Star dunes (reviewed
by Lancaster 1989) usually have a central peak that is higher
than any other part of the dune, from which three (or more)
distinct, often sinuous arms extend radially away from the
central peak. Each arm can display a separate slip face

Fig. 6.14 More barchans and barchanoid ridges, North Polar Erg.
PSP_007676_2650, 2 m/p. The dunes and the interdunes here are all
covered in CO 2 frost, although a few dark spots indicate where sand or
dust has broken through the frost. Image credit NASA/JPL/U.Arizona