ABSTRACT
Active sand dunes cover about a quarter of deserts, and stabilized sand dunes cover somewhat more of the semi-arid lands. Active sand dunes are all highly mobile and highly unstable, but ground conditions vary considerably. The elemental dune, the transverse dune, is delicately adjusted to ambient wind conditions. The main portions of the leeward and windward slopes are very loose. The dune “cap” is firmer. The mobility of these dunes is controlled mainly by size and wind speed. Dunes are divided in to transverse, zibar, linear, network and star. Transverse and network dunes are the most mobile. Zibar are coarse-textured dunes that have generally stable surfaces. In linear and star dunes, crests may be mobile and unstable, but plinths are stable. Ground conditions are much less of a problem on stabilized dunes, where, in general, slope angles are lower, but these surfaces also contain distinct challenges, such as water-repellency and textural B horizons.
