Evolution of the Rub‘al Khali desert

Abstract EN

The Rub* a) Khali is the world's largest contiguous sand dune desert (640.000 km2 area).

It originated only during the Late Quaternary.

Earliest low-rounded dunes within this desert are of Middle Pleistocene age; approximately 700,(XK) years old.

No evidence exists of any desert sand dunes in the area during the early part of the Quaternary Period.

Several Late Quaternary pluvial phases of most notably from -17,000 to -36,000 years, oc- curred with high lake levels in the southwestern Rub* al Khali and periodic streams flowing to a muc?h diminished Arabian Gulf.

There were also much vegetation and wildlife.

Stone Age man prospered, with his distinctive arrowheads found around old lake bed margins in the Rub* al Khali.

A moderately arid interval (-10,01H) to-17,000 years) with lakes low or absent was fol- lowed by an Early Holocene pluvial phase (-6,000 to-10.000 years).

Lakes were again present in the southwest, with abundant surrounding Neolithic flints, and streams flowed intermit- tently.

The last phase of the Holocene (-6,000 years to present-day) has been mostly hyperarid with slightly moister intervals.

High-crestcd, longitudinal dunes (*uruq)of the Rub* al Khali formed during this phase.

These dunes typify vast areas of the Empty Quarter, being widely spaced and up to 230 m high.

They are draa dunes, plus some oblique seif dunes, barchans and zibars.

Formation of these huge longitudinal dunes is due to vortex-type wind flow alternating from the northeast and southwest.

During the last 6,000 years, very limited surface wadi flow occurred within the Rub* al Khali and cities like Qaryat al Fau flourished under a slightly milder climate from -1,400 to -2,100 years when limited irrigation was possible in peripheral areas.

Longitudinal, transverse and solitary dune types found in the Rub* al Khali are described with examples and a brief explanation of the dynamics of their formation.