Dahlak - The islands

Dahlak THE ISLANDS

		The Dahlak seem rafts just emerging from the waves. The beaches are white because they consist exclusively of limestone from the destruction of coral reefs. Large sections of the Dahlak’ costs are made up of low cliffs carved at the base to be pitched, worrisome about stability. Behind their origin is the erosion caused by waves, associated with the gastropod mollusks grazing that scratch the rock in search of the algae they eat. The presence of these structures in some areas well above sea level, or 10-20 m deep, is proof of the continued outcropping of the islands and changes in sea level. In the more sheltered

bays grow mangroves, tropical trees belonging to various families united by their ability to grow in seawater, although in areas at least partially sheltered from the swell. Sprouts in fact are able to settle only in calm waters. It is an environment ecologically very important because it is an oasis of high productivity in a coastal environment that for what remains is desert. Indeed, the dead branches and leaves enrich the soil and the sea with organic material that forms the basis of a food chain that includes fish of great economic importance. The wood of mangroves is also the only easily available in a coastal habitat nearly desert and a

		project, already started, on the coast shoot for repopulate some areas that were overgrazed in the past. The inland of the islands is wind-blown by the northeast monsoon, which in the winter go up along the Red Sea, bringing rain to the entire southern area. Rainfalls are less than 200 mm per year, but that is enough to turn green again the islands. The Dahlak fall into what the phytogeographers called "ethiopian arid shrublands and grasslands”, but there has never been extensive botanical research and the most authoritative date back to those made at the end of the nineteenth century by Achille Terracciano, University of Sassari,

who visited a dozen islands and put together more than a hundred species. The fauna has been little studied, and if we are not surprised by the presence of a dozen species of reptiles, different matter is the case of three species of amphibians. In fact they can not survive in seawater and should be arriving in the area when, during the last Ice Age, the rock platform that includes the Dahlak was connected to the mainland due to the lowering of sea level. Few are mammals species: blacks rats, cats and gazelles, a couple of species of bats, mice and shrews still unidentified and apparently nothing else. All that perhaps once lived on the islands has

probably been extinct for the progressive desiccation and the direct action of man against those species who could be a danger to himself and his herds.

Dahlak THE ORIGIN OF THE ISLANDS

		The more than 200 Dahlak real belong to the Red Sea. In fact. unlike many islands that are fragments of the continent or remains of volcanoes, the Dahlak formed by coral reefs that emerged from movements caused by the separation of Arabic clod from the African one. This separation reached a development similar to the current during Oligocene Era (38 to 24 million years ago) forming a sea that was at the time connected only to the north by the Mediterranean, without connection with the South Indian Ocean. At the end of Miocene Era, between the 5, 7 and the 5 million years ago, the earth movement towards north Africa almost closed the Strait of

Gibraltar, slowing the exchange of waters with the Atlantic Ocean. At that time, much more water evaporate in comparison to the one that entry as a cascade from the Strait of Gibraltar, so that the sea level lowered and salinity increased. On the bottom then set down huge layers of salts that, under the Dahlak, reach a thickness of more than 3 kilometres. Subsequently the connection between the Red Sea and the Mediterranean close down and opened a connection to the south with Indian Ocean. Slowly the erosion of the coasts overlaid the salty deposits with a layer of clay, sand and gravel. The complex movements of lithosphere connected to the

		separation between Africa and the Arabian Peninsula led to a gradual lifting of the platform that includes the Dahlak and, when the seabed was not deeper than 50 metres, began the training of thick coral reefs that are now the rocks of Dahlak. The process of growth of the corals took place in the last interglacial stage, between 200.000 and 120.000 years ago, but was interrupted when, occurring in the same period with the last Ice Age (10.000 years ago), the water cool down and the sea level lowered exposing coral reefs. Due to the melt of glaciers the level of the Red Sea start again to rise, but it reached the current level only 5000 years ago, giving to

the Dahlak the look that we know. The corals that you can admire today at the Dahlak, are therefore of recent origin. But the actual formation of the islands has been dependent on local tectonic movements, still in progress, caused by masses of salt underlying heavier sedimentary rocks. In fact, when it formed a crust, a fracture in rocky layers, and the heavier rocks overlooking the saline layers, they could tilt forming higher areas , the islands, and areas of the deeper sea.