Page 156 - Arabian Studies (II)

SOME EFFECTS OF IRRIGATED
AGRICULTURE ON SOIL

CHARACTERISTICS IN RAS
AL-KHAIMAH, UNION OF ARAB

EMIRATES
by J. H. STEVENS

1. The Physical Environment

The lowland area of Ras al-Khaimah is mainly composed of
sedimentary deposits derived from erosion of the Ru’us al-Jibal/Hajar
highlands to the east (Fig. 1). The latter rise to a height of over 2000
metres and are mainly composed of limestones, dolomites and marls
of Permian to Upper Cretaceous age. Erosion of this upland area has
taken place in several stages and this has resulted in a complex
sequence of outwash deposits. The effects of Quaternary events on
soil development have been summarised by Stevens (1969).
In the area under study, there are two types of outwash — the
outwash fans that have coalesced and been modified to form the Jiri
Plain, and the smaller, well-defined fans that occur along the
mountain edge, north of Habhab. The erosion of the uplands, with
the subsequent transportation of the eroded material, was most
marked during pluvial periods. This, according to Butzer (1963),
corresponded to the Wurm Early Glacial period in Europe. After the
pluvial period, as the climate became progressively drier and/or hotter,
evaporation of a high water table resulted in the formation of
gypsum crusts, relics of which can still be found further south on the
Gharif and Madam Plains. At the same time, occasional heavy
rainfalls resulted in the erosion of the outwash fans causing them to
become deeply trenched while the fine sediments (silts and clays)
were deposited further west. A period of aeolian activity then
followed which resulted in the partial infilling of the erosion gullies,

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