 |
|
|
|
|
|
|
|
|
|
|
|
|
Tectonics : the Mediterranean Sea [2]
Tectonique : la Méditerranée [2]
The Earth : In the Mediterranean Sea - Meditate... [Genista]
By Nicolle Mathé, 'Genista Informations' No 301, March, 2004 (Plate tectonics)
|
![the Earth [la Terre]](../../i/globe.gif)
The East basin of the Mediterranean Sea, which is what remains of the former ocean formed by the Tethys, must be fascinating
geologists of all specialities because of the old oage of its floor and the movements of its numerous microplates.
The auscultation of its faults can allow to predict a series of major catastrophes along its edges.
|
The result of a hypocollision
The stitch line between the plates which have collided — the Africa-Arabia block against Eurasia —
is very clear in Calabria, in the Apennines, the Dinarid Alps (North Albania and former Yougoslavia).
It is well marked between the Hellenides (the rest of Albania, Macedonia, Greece) and the Near-East where
there is the forming of the Egean Arc.
Those lines are clearly marked by the rocks which compose them (basalte...),
torn away from the oceanic crust of the descending plates in the subduction zone between Africa and Eurasia
and trapped in the continents under the form of overlapping scales during their collision.
![the Arabian plate and the Red Sea [la plaque arabique et la Mer Rouge]](it/plaqarab.gif)
How deep !
The deplorable accident of the Charm el Cheikh plane, in Egypt, in January, 2004, in the Gulf of Aqaba,
6,000 ft deep (1830 m), has brought the cable-layers, specialists of oceanic depths, to locate the black boxes of the
damaged plane with great difficulty.
In fact, the Red Sea, 124 to 186 miles wide (200 to 300 km), is in some places 9,967 ft deep (3,040 m) !
Its floor is being built from a central recent oceanic rift, and this accretion causes a pressure on Africa, to
the West, and Arabia, to the East. This young ocean is the unexpected study ground for the mechanism
of the forming of an ocean.
|
What connection is there ?
(Click on the map to get a full-screen picture)
Use your Browser to come back to this Page (PREVIOUS)>
![general geological map of the Mediterranean Sea [carte géologique générale de la Méditerranée]](it/meditsea.gif)
This ocanic rift id linked, to the South-West, with the low floors or intracontinental rifts
of East Africa, to the East, and, to the North-East, the fault corridor which starts in the Gulf of d'Aqaba,
reaches the Dead Sea, the Jordan valley, the Tiberiade Lake, the trenches of the Bekaa and the Ghab in Syria, and reaches
the slopes of the Taurus Mounts in Turkey, through the Levant fault.
There, we have :
the limits between the Arabic plate and the African plate, which were geologically joined,
the explanation of the sliding of the Arabic plate towards the North-East,
1 5/8 inch (4 cm) every year, alonge the Dead Sea fault
and the strong seismic activity in this long corridor (Alep in Syrie in 1872 : 7,2 — Beyruth in
Lebanon in 1956 : 6 — Israel in 2004 : 5,1),
the origin of the forming of the Caucasus range, because the Arabic plate acts like a punch
which distorts Eurasia and pushes Iran and Turkey sideways along the North-Anatolian fault.
The Red Sea is also communicating with the Mediterranean Sea, through the Suez Gulf, which is shallow —
262 ft (80 m) — at the end of which has been dug the Suez Canal, 100 miles long (161 km), which was completed
in 1869.
The Turkisk microplate
Being pushed by the African and Arabic plates, the Turkish microplte is blocked along the edge of the
Eurasian plate, and it slides along the North-Anatolian fault which ranges from the Egean Sea as far as Iran.
![the Turkish plate and the North-Anatolian fault [la plaque turque et la faille nord-anatolienne]](it/plaqturc.gif)
It forms a fold on the Anatolian peninsula, and generates the collision range of Caucasus, the seismic activity of
which is well-marked (Spitak in Armenia in 1988 : 7 — Bam in Iran in 2004 : 6,3).
It is sucked towards the West because of the progressive plunging of the Egean plate on which Greece lies, among others.
It is along the North-Anatolian fault that major earthquakes have come in succesion, during the past sixty-five years
(Erzincan in 1992 : 7,1 — Izmit in 1999 : 7,4).
This plate moves in portions 62 to 93 miles (100 to 150 km), with two blocks moving 1 inch apart (2·5 cm) per year,
viz. 20 times faster than the active faults in France. The accumulated forces are released abruptly on one of the blocks and,
the more time has elapsed, the more energy is accumulated, the stronger the discharge of energy is.
The tensions move towards the West in the Sea of Marmara, and Istanbul is all the more threatened as this fault
has not been moving for a long time under the city.
The Egean microplate
The Egean microplate is also located between the African plate and the Eurasian plate. In this case,
to the South of Crete, a ridge has been found, which is 124 miles (200 km) wide, and 1,180 miles (1900 km) long,
from Apulia (the Italien Puglie) to Cyprus. To the South of this ridge, there is principally an abyssal plain,
which is invaded by the alluvial deposits of the Nile, covering an area of 38,600 sq. miles
(100 000 km2).
Being pushed towards the North by the activity of the ridge, the rest of the oceanic crust of the Tethys moves by subduction
under the Egean plate, causing the forming of a double island arc oriented North-West–South-East :
one is outside, it is sedimentary, non-volcanic : Cythere, Crete, Kassos, Karpathos and Rhodes.
the other is inside, with andesite volcanoes caused by subduction : the Methana peninsula, the islands of Poros, Milo,
Santorino (with its cataclysmal eruption, in 500 B.C., which destroyed the Minoan civilization), and Nísiros.
Double faults, oriented North-West—South-East and North-East—South-West make like a draughtboard of islands
in which the seismisc activity is very important, with seismic centres 155 miles (250 km) deep.
|
The Red Sea is an expanding ocean whereas the subduction in the East basin is about to terminate.
Could this be the omen for an evolution towards a sea that would be similar to the Caribbean Sea ?
All these movements of plates make us to fear a more important seismic and volcanic activity, particularly in Turkey
and in Greece where 80 per cent of the seismic activity of the Mediterranean basin are concentrated.
|
|
In 2000 B.C., Sodome et Gomorrhe, located on the banks of the Dead Sea, were destroyed by an earthquake, a volcanic
eruption, and they were submerged by the water of the Mediterranean Sea which, because of the sinking of the Dead
Sea, was swallowed down into this depression.
Then, the water evaporated and an important amount of salt was deposited, Loth's salt – Loth, the only survivor
of Sodome and Gomorrhe, together with his son. The amount of salf is high, 26 %, and this is perhaps a happy thing
for bad swimmers, who do not have to fear they will be changed into salt statues, but it does not help
the development of life.
The sea, 2623 ft (800 m) deep, is located at the lowest level on Earth (–1311 ft, or –400 m), and
it is becoming lower and lower regularly.
Downstream, the water of the Jordan River which flows into it is pumped for cultures, and a canal, several kilometres long,
also plays a part in the dying of this sea which is now parted into two parts by a strip of land.
The Jordan, which has its springs in the Antiliban, flows towards the South and goes through the
soft water lake of Tiberiade, to flow into the Dead Sea. The springs of the Jordan are located in Lebanon, in Syria
(Banias) and above all in Israel, with some fifty springs and artesian wells, Dan being the more abundant with
8,810,000 gallons (40 000 m3) per hour, in winter time as well as during the summer.
There is a project to build a canal from the Red Sea to the Dead Sea, or an underground canal from the Mediterranean Sea
to the Dead Sea, and this could salvage this sea.
|
|
|
|
|
|
|
|
|
|
|
![general geological map of the Mediterranean Sea [carte géologique générale de la Méditerranée]](it/meditbig.gif)
Haut de Page • [Top of Page]
Part 1 : The Mediterranean Sea : a jigsaw puzzle • [Première Partie : La Méditerranée : un puzzle]