Offshore Islands

Whereas the mainland coast and associated islands consist of recent sedimentary carbonates, the isolated offshore islands have a much older origin. Through a process of salt diapirism the cores of these islands are pre-Cambrian Hormuz outcrops, which have pierced the earth's surface at the highest point of the salt dome to form conical hills. In Pleistocene times, low carbonate plains accumulated around these hills, along with associated coral reefs, particularly on the more protected south and east sides. None of the islands is very large, and because most have no natural source of fresh water (Delma is an exception), they were generally uninhabited until recently when a few of them were adopted as bases by oil companies. One or two of the islands, such as Sir Bu Nuair, reveals deposits of igneous rock, and the numerous fissures are often rimed with yellow sulphur deposits. Jebel Dhanna is the one example in the country of these formations that does not in fact lie off-shore. The hills of these islands are steep and deeply incised as a result of erosion, and the original elevations are now much reduced, though the summits are still higher than any point on the corresponding coast, apart from Jebel Dhanna. Zirku for example rises to 130 m, compared with 33 m for the highest point of the road between Qatar and Abu Dhabi. The coastline of these islands consists of undercut limestone ledges up to 3 m high and a few tiny sandy coves. Only the larger islands have developed miniature shallow wadi systems fanning out from the hills (Alsharhan et al. 2002).