As most of it formed some 600 million years ago, the Sinai mountain range is one of the World’s oldest massifs. Apart from the red granite rock which takes up 80 % of the Sinai High Mountain Region, there are newer, 10 million year-old black volcanic rock formations. The interconnected labyrinth of valleys were created by the rains and melting snow, and are dotted with gigantic boulders brought down by the enormous force of water. Regular flash floods still sweep through the wadis, causing damage to gardens and buildings, but at the same time replenishing the underground water catchment basins on which the very same gardens depend on.
The South Sinai massif is part of the Arabo-Nubian massif. Its mounts are mainly magmatic, that is, originate from the magma, or the molten rock below the earth’s crust. Towards the end of the Precambrian, around 600 million years ago, large bodies of molten magma began intruding upwards toward the surface, cooling, and thus solidifying into rock. The many kinds of rock found in the region of the South Sinai massif, formed by the cooling process mentioned, may be classified into three main groups:
1. Plutonic granites, were formed deep beneath the surface. The cooling was relatively slow, and their crystals are typically large. Jabel Rabba, Jabel Safsafa and Jabel Er-Deir are examples of mounts of this type of granite.
2. Volcanic rocks, where formed of magma which erupted to the earth’s surface, cooled quickly, and their crystals are too small to be distinguished by the naked eye. J. Katerina, J. Musa and (the upper portion of) J. Abbas Basha are examples of mounts of volcanic rocks.
3. Dykes, where formed by magma which broke its way upwards in cracks and fissures. It cooled rather quickly, but at a slower rate than volcanic rocks. Dykes are typically of crystal size between plutonic granites and volcanic rocks. Dykes can be seen in great numbers and in a variety of sizes throughout the South Sinai massif. The typical structure of a dyke is either a gully with vertical walls and fractured base, if its erosion is more intense than in the hosting rock, or an outcrop, if its erosion is lower than in the hosting rock.
Dykes are the stripes of volcanic rock intrusions which sometimes stretch for kilometers and can be many metres in width. Dykes are usually a darker red or grey colour than the surrounding rock and are more permeable to water than the harder granite. Underground springs are more likely tapped here than anywhere else. Plants grow more easily along dykes and animals congregate to feed and take shelter here. Bedouin refer to the dykes as “jidda”, meaning grandmother – the nurturer, the nourisher. Jidda is probably also a corruption of the formal Arabic word “gaedda”, which means dyke.
Other types of rock, such as metamorphic, sandstones, or limestone, although found in other areas of Sinai, are quite absent from the South Sinai massif.
After their formation, these magmatic rocks were deeply eroded, and then covered by layers of sedimentary rocks for most of their subsequent lifetime. These sediments were formed either at the bottom of a rather shallow ocean, in which case limestone layers and their relatives are found, or on the continent itself, in which case sandstone is found.
It was only relatively recently, during the Miocene (about 20 million years ago), that stresses and motions in the crust brought about an uplifting of the area which today comprises the South Sinai massif, accompanied by two important phenomena: 1. Erosion of the sedimentary layers and thus exposure of the magmatic rocks, and 2. Creation of faults, firstly connected with the formation of the Gulf of Suez on the west, and then with the formation of the Gulf of Aqaba on the east.
The granite is composed mainly of three minerals: Feldspar, Quartz and Mica. The Feldspar and the Mica portions, with the addition of water, may convert, under favorable conditions, into clay minerals, in which case the rock texture disintegrates, as if the cement between the bricks of a wall is removed, and the wall then looses its strength.
As the Sinai granite has not been exposed for long, and the climate is very dry, not much of the Sinai granite has undergone this disintegrating process, except in locations where humidity tends to persist. On the whole, whatever little erosion occurs in Sinai, is chiefly mechanical, rather than chemical.
At exposed surfaces the humidity is low, and whatever friable material is formed – it is soon removed by winds and rains. Exposed surfaces in Sinai, therefore, are in most cases fairly solid.
In gullies and dry waterfalls humidity is maintained for prolonged periods of time after a rain event, and the disintegration is therefore considerable. However, in gullies and dry waterfalls the disintegration materials is flushed away by the next water stream, and solid rock is left behind.
In sloping walls, wherever an irregularity of the surface forms a pocket, water is retained. The erosion increases the size of the pocket until it touches the neighboring pocket, and creates a layer of friable material beneath the surface, covering large areas of the wall, with typical “coves” and “bridges” imbedded in it.
Onion-like structures are fairy common in Sinai, seen mostly as “belts” separating between “slabs”.
The NE wall of J. Safsafa (on both sides of the Boustan Gully), The “Little Rabba”, and the W wall of J. Rabba (near the Um-Surdi pass), are examples of such onion-like structures. This feature is not yet well understood, and is often attributed to weathering, rather than to some process which might have occurred during the magma solidification.
Nature Notes: Rays of God or Dendrites
On some rock faces a black leaf-like pattern can be seen. Some people believe that the patterns were caused by divine light so intense that it imprinted the shadows of living plants on stone and that it is reminiscent of the leaves from the Burning Bush.
• Climbing in Santa Catherine area in South Sinai
• Wadi Arbaein & Wadi Shrayj, A Walking Trail Guide – National Parks of Egypt Protectorates Development Programmes
• Mount Sinai, A Walking Trail Guide – National Parks of Egypt Protectorates Development