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Geologie Sinajského poloostrova

22.01.2011  |  215× přečteno      vytisknout článek 

Sinajský poloostrov, o který se v minulém století vedly velmi intenzivní boje mezi Egyptem a Izraelem leží mezi Afrikou a Asií. Podívejme se trochu na jeho geologickou skladbu.

Sinai, the triangular-shaped peninsula of Egypt, is situated between Asia and Africa. The separation of the two continents caused the form and geographical shape of Sinai the way it looks today.

Sinai, the triangular-shaped peninsula of Egypt, is situated between Asia and Africa. The separation of the two continents caused the form and geographical shape of Sinai the way it looks today.

Sinai is approx. 380 km long (north - south) and 210 km wide (west - east). The surface area has an extension of 61.000 km^2, the coasts are streching about 600 km on the west and on the east. On the western part there is the Gulf of Suez (with the Suez channel) and the eastern part of Sinai brings up the much deeper Gulf of Aqaba. The sea in the Gulf of Suez measures approx. 80 meters only, while the profile of the Gulf of Aqaba goes down to approx. 1.830 meters. The latter is a part of the big land rift that extends until Kenya.
Huge seismic activity and the tremendous eruptive phenomena have given Sinai its characteristic looks. 
The highest mountains are the Gebel Musa (Moses´ mountain) with 2,285 metres, and the Sinai's highest mountain Mount St. Catherine (Gebel Kathrina) with 2,642 metres. Many of the Pharaohs got their precious stones from  southern Sinai.
 
 
 
 
The region was formed as a result of tectonic plate movement: the African, Arabian and Mediterranean shields pulling away from each other, creating a great gash in the land. 
 
At the same time, the outward movement pushed against existing rock layers forming the looming Sinai Mountains. The effect was extensive, extending from what is now the Jordan River valley, south, then south east, turning at Djibouti into Kenya - thus becoming known as the Great Rift Valley .

Two gulfs were created as branches to this valley. The Gulf of Suez leading to the Suez canal, is relatively shallow [60-90 meters] compared to the impressive depths of the Gulf of Aqaba - 1000- 2000m in some places.

The peninsula of Sinai can be divided into a northern and a southern region. 
 
The North consists of flat lying Palaeozoic [550 million years] and more recent sediments, while the South consists mainly of metamorphic and magmatic rocks which are of Precambrian age [more than 600 million years]. This southern portion is a continuation of the Arabio-Nubian Desert. A narrow belt [30kms wide] of soft Nubian sandstone also contains most of the Sinai minerals eg. turquoise, manganese, copper. The magmatic rock now occupies some 60% of the southern part of the peninsula and is responsible for the 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, Musa and Catherine.

In the southern part, you can see below the sandstone belt, the granite mountains rising to peaks of more than 2,638 m [7,000 feet]. The polymorphic rocks in Sinai were last formed about a thousand million years ago. 
 
At that time along the southern portion of Sinai, a north-south belt of volcanic islands were active following their deposition in a great oceanic basin. As a result, large quantities of lava accumulated in this area at the same time as assorted sediments were deposited in adjoining basins due to erosion.

The more colored granites are much older than the reddish rock. 
 
These dykes [fine grained basaltic intrusions], having pushed their way into the original coarse grained plutonic granites, created stunning effects of color and form. To this is added the effects of sandstone weathering and coloring through leeched minerals. In some places, a whole hillside is layered in all colors - red, purple, green, cream, white, orange. In many places the evidence of past geological activity is obvious with tilted layers sitting on the underlying granite.


The Suez rift, Sinai, Egypt, is the NW-SE-trending arm of the Cenozoic Red Sea rift system, formed in response to late Oligocene / early Miocene rifting of the African and Arabian plates (a rift system is a sedimentary basin that forms by heating and thinning of the crust and lithosphere at the time of rifting). 
 
It is 300 km long and up to 80 km wide, and is delineated on both margins by large-scale normal fault systems, which define classic half-graben-style tilted fault blocks, typically up to 20 km wide (a half-graben is a wedge-shaped basin in cross section that develops as the hanging-wall block above a normal fault slides down and rotates; the basin develops between the fault surface and the top surface of the rotated block). The area is characterized by deeply incised wadis and a lack of vegetation which provides excellent 3D exposure of fault zones and stratigraphy.

 Sinai Peninsula is a meeting point for the three great religions, at the crossroads of Africa and Asia. 
 
It lies at the northeast comer of Egypt, covering an area of about 61.000 km2 and is bounded by the Mediterranean Sea at the north and Ras Mohammed at the south. The eastern and western boundaries are the Gulf of Aqaba and Gulf of Suez. The Gulf of Suez rift lies within the Arabo-Nubian shield, a segment of upper Proterozoic to lower Paleozoic continental crust formed during the widespread Pan-African thermal event; this crust forms the fundament of much of northeast Africa and western Saudi Arabia.

The Red Sea is a tectonic spreading zone (red line in the map below) and part of the Great Rift system that runs from northward in Turkey, down through the Dead Sea, the Red Sea, and southward deep into the African continent. The average depth of the Red Sea is between 2,500 and 3,500 feet, although in places it is estimated to be around 7,200 feet deep. 
 
The Red Sea stretches north from the straits of Bab el-Mendeb to the city of Suez, a distance of 1450 miles. Its maximum large is around 205 miles. At Ras Mohammed , in the north, the Red Sea is split by the granitic peninsula of Sinai into two gulfs - the Gulf of Suez and the Gulf of Aqaba.

The Red Sea, the only enclosed coral sea in the world, is a distinctive and unique tropical sea - an unparalleled source of entertainment and beauty. 
 
Running as a narrow strip between Africa and Arabia for 1500 miles, the Red Sea joins at its southern tip the Indian Ocean through the Strait of Bab-El-Mandab, while at its northern head it branches into the twin gulfs of Suez and Aqaba. Unlike the arid lands of desert and semi-desert on either side, the Red Sea is framed with thousands of untouched coral reefs, oases of teeming under-water life basking into its shallow waters.

The Red Sea is characterized by its high salinity - a consequence both of the hot climate and the absence of any river adding fresh water to the sea. The surface sea temperature ranges, according to the time of the year, from approximately 20 to 26 degrees Celsius in the northern part, and from 25 to 31 degree C in the central and southern parts. Clear skies, strong sunlight and the absence of inflowing sediments contribute to excellent underwater visibility, leading to the Red Sea waters being among the clearest waters in the world. 

The normal tides are small and occur on a semi-diurnal (twice a day) basis, with the whole sea oscillating around a nodal point approximately at the latitude of Port Sudan. The Peak tides, at the northern and southern ends, are of about half a meter, while in the center there is no virtual daily tide. There are, however, throughout the Red Sea, seasonal variations in water level over a longer period, the mean water level in Summer being nearly a meter lower than it in Winter. 

The Seasonal tides, and the pattern of prevailing winds and currents, are all influenced by the change between summer and winter monsoons in the Indian Ocean. During the summer northerly winds prevail through the whole Red Sea, the main surface current generated by these winds is to the south, and water is driven out of the Red Sea, thus lowering its level. During winter the prevailing winds are still northerly in the northern half, but in the southern part are from the south, and these winds generate a northerly current, thus bringing water back into the Red Sea again. 
ZDROJ:http://rassudrsinai.blogspot.com


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