The Geology of the Sinai Desert
“The change from sandstone to granite as one leaves Jebel Mukatteb and winds along Wady Feiran is very striking. Even to the most uneducated eye the colours tell their own story of chalk and limestone and sandstone and granite. The mountains are streaked from head to foot as if boiling streams of dark red matter poured over them, the vast heaps of seemingly calcined mountains, the detritus iron in The sandstone formation, the traces of igneous action on the granite rocks are dating from their first upheaval” Sir Charles Wilson, Picturesque Palestine.
The Sinai peninsula is enclosed by the two spectacular branches of the African Rift Valley – the Gulfs of Aqaba and Suez. Since at least 25 million years ago these, and many related rift faults in the interior of the peninsula, have played a dominant role in the geological evolution of Sinai.
The total area of the Sinai is 61,200 sq km. Sinai is the crossroads between Asia and Africa on the one hand, and the Mediterranean and the Indian Ocean on the other.
The peninsula can conveniently be divided into a northern and a southern region. The North consists of flat lying Palaeozoic and more recent sediments, while the South consists essentially of metamorphic and magmatic rocks which are of pre-Cambrian age. This southern portion is a continuation of the Arablo-Nubian Desert.
The central Et-Tih plateau of Sinai is virtually unpopulated, but at the foot of Et Tih to the south are the wide sand plains. In rainy years they provide some pasture and are easier to traverse. This narrow belt (30 km wide) of soft Nubian sandstone also contains most of the Sinai minerals, e.g., turquoise, manganese, copper.
Below this sandstone belt the granite mountains appear, rising to peaks of more than 7,000 feet. This area has water, beautiful oases and many gardens. Some of the valleys carry water all year round.
The metamorphic rocks in Sinai were last active about a thousand million years ago. At that time along the Eastern portion of Sinai, a north-south belt of volcanic islands were active following their deposition as ancient marine sediments in a great oceanic basin, As a result, large quantities of lava accumulated in this area at the same time as other assorted sediments were deposited in adjoining basins due to erosion.
At a later date, widespread intrusion of granite batholiths and plutons took place. This resistant rock now occupies some 60% of the southern part of the peninsula and is responsible for the most magnificent peaks (Gebel Serbal) and deepest canyons (Dahab).
There were several periods of intrusion and dyke swarms before a brief burst of younger volcanic activity, e.g., Gebel Musa and Catherine.
