Most of the surface of the present day UAE is a sand desert, stretching from the Arabian Gulf coast south to the unbroken and uninhabited sands of the Empty Quarter, and east to the gravel plains bordering the Hajar Mountains. The desert is a geologically recent feature, the result of prolonged subaerial erosion and deposition in an arid environment. The sands overlie the thick, oil-rich sedimentary strata of the Arabian Platform which constitutes the bedrock of most of the UAE, but the oil producing rocks are nowhere exposed at the surface, and are known only from drilling.
In many areas near the coast, the sand is stabilized by vegetation, although the natural flora has been altered in recent times by extensive grazing of domesticated animals. Further inland the sands may be quite barren, as few plants can successfully colonize the mobile dunes.
Dune Patterns
Sand dune formation is controlled by a combination of wind strength and direction, and sediment supply. In detail, however, the formation of dune patterns is complex and remains poorly understood. Within a given area the dune pattern may be quite regular, but also very intricate. Physical features are typically created on several different scales: giant sand ridges on a scale of hundreds of metres to a few kilometres, sand dunes measured in metres to tens of metres, and ripples on a scale of centimetres to a metre or more. This hierarchy can be readily observed in the deserts of the UAE.
Since dune patterns vary with wind direction, seasonal or occasional variations in wind direction introduce new elements into the overall pattern. These elements may reinforce or cancel each other, in the same manner as ocean waves. In addition, because sand dunes cannot move or change as quickly as ocean waves, past history may play a significant part in what we see today. Despite relatively consistent prevailing wind directions in the present day UAE, dune patterns and alignment vary considerably from area to area .
The Effects of Climatic Change
The largest dune features of the present day UAE, including the major transverse dunes of Liwa and Manadir, the smaller eroded dune ridges of the Northern Emirates, and the longitudinal dunes of the south-west, are believed to date from the most recent glacial period, more than 10,000 years ago. A glacial origin for these major features is consistent with the fact that they do not seem to be aligned with today’s prevailing winds.
The present day wind regime appears to be transporting material from the coast inland and reworking the surface of the major earlier structures without, so far, removing or reorienting them. For example, one may observe between Abu Dhabi and the Liwa oasis that extensive tongues of pale sand resembling a choppy sea of dunes (aligned NE-SW) are filling in broad troughs between higher, flatter ridges of red sand (aligned WNW-ESE). The latter are known as suruq , or easy travel zones, and are interpreted as the eroded cores of older, larger ridges. Further inland, however, the major transverse dune ridges of Liwa and Manadir are neither in motion nor are they being eroded at the present time, although the smaller dunes on their surfaces conform to present day winds.