Biographie dun désert: Le Sahara (French Edition)

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Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. The Editors of Encyclopaedia Britannica. Learn More in these related Britannica articles: In the semiarid zone of north-central Sudan, the layer of rock waste is slightly modified to form immature soils; in the Qawz region, soils are brownish red and of low fertility.

The highest point in the desert is the 11,foot 3,metre summit of Mount Koussi in the Tibesti Mountains in Chad. The lowest, feet metres below sea level, is in the Qattara Depression of Egypt. They also occur, however, as small isolated dunes on hard desert surfaces, covering an area of as little as 10 square metres square feet. Areas of gently undulating sandy surfaces with low relief…. Geology Sahara In Sahara: Physiography Sudan In Sudan: In the southern Sahara, the drying trend was initially counteracted by the monsoon , which brought rain further north than it does today.

By around BCE, however, the monsoon retreated south to approximately where it is today, [31] leading to the gradual desertification of the Sahara. The Sahara pump theory describes this cycle.

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During periods of a wet or " Green Sahara ", the Sahara becomes a savanna grassland and various flora and fauna become more common. Following inter-pluvial arid periods, the Sahara area then reverts to desert conditions and the flora and fauna are forced to retreat northwards to the Atlas Mountains , southwards into West Africa , or eastwards into the Nile Valley.

This separates populations of some of the species in areas with different climates , forcing them to adapt , possibly giving rise to allopatric speciation. It is also proposed that humans accelerated the drying out period from 6,—2, BCE by pastoralists overgrazing available grassland. The Red Sea coastal route was extremely arid before and after kya. Slightly wetter conditions appear at 90—87 kya, but it still was just one tenth the rainfall around kya.

This suggests that the southern Negev was arid to hyper-arid in these periods. During the Last Glacial Maximum LGM the Sahara desert was more extensive than it is now with the extent of the tropical forests being greatly reduced, [35] and the lower temperatures reduced the strength of the Hadley Cell. This is a climate cell which causes rising tropical air of the Inter-Tropical Convergence Zone ITCZ to bring rain to the tropics, while dry descending air, at about 20 degrees north , flows back to the equator and brings desert conditions to this region.

It is associated with high rates of wind-blown mineral dust, and these dust levels are found as expected in marine cores from the north tropical Atlantic. The moister Saharan conditions had begun about 12, BCE, with the extension of the ITCZ northward in the northern hemisphere summer, bringing moist wet conditions and a savanna climate to the Sahara, which apart from a short dry spell associated with the Younger Dryas peaked during the Holocene thermal maximum climatic phase at BCE when mid-latitude temperatures seem to have been between 2 and 3 degrees warmer than in the recent past.

Analysis of Nile River deposited sediments in the delta also shows this period had a higher proportion of sediments coming from the Blue Nile , suggesting higher rainfall also in the Ethiopian Highlands. This was caused principally by a stronger monsoonal circulation throughout the sub-tropical regions, affecting India, Arabia and the Sahara. This is linked to a marked decline in the scale of the Nile floods between and BCE.

The Sahara comprises several distinct ecoregions. With their variations in temperature, rainfall, elevation, and soil, these regions harbor distinct communities of plants and animals. The Atlantic coastal desert is a narrow strip along the Atlantic coast where fog generated offshore by the cool Canary Current provides sufficient moisture to sustain a variety of lichens , succulents , and shrubs.

The North Saharan steppe and woodlands is along the northern desert, next to the Mediterranean forests, woodlands, and scrub ecoregions of the northern Maghreb and Cyrenaica. Winter rains sustain shrublands and dry woodlands that form a transition between the Mediterranean climate regions to the north and the hyper-arid Sahara proper to the south.

The Sahara Desert ecoregion covers the hyper-arid central portion of the Sahara where rainfall is minimal and sporadic. Vegetation is rare, and this ecoregion consists mostly of sand dunes erg, chech, raoui , stone plateaus hamadas , gravel plains reg , dry valleys wadis , and salt flats. The South Saharan steppe and woodlands ecoregion is a narrow band running east and west between the hyper-arid Sahara and the Sahel savannas to the south.

Sahara | Map & Facts |

These rains sustain summer pastures of grasses and herbs, with dry woodlands and shrublands along seasonal watercourses. In the West Saharan montane xeric woodlands , several volcanic highlands provide a cooler, moister environment that supports Saharo-Mediterranean woodlands and shrublands. Higher and more regular rainfall and cooler temperatures support woodlands and shrublands of Date palm, acacias , myrtle , oleander , tamarix , and several rare and endemic plants.

The Saharan halophytics is an area of seasonally flooded saline depressions which is home to halophytic salt-adapted plant communities. The Tanezrouft is one of the harshest regions on Earth as well as one of the hottest and driest parts of the Sahara, with no vegetation and very little life. It is along the borders of Algeria, Niger, and Mali, west of the Hoggar mountains.

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The flora of the Sahara is highly diversified based on the bio-geographical characteristics of this vast desert. Floristically , the Sahara has three zones based on the amount of rainfall received — the Northern Mediterranean , Central and Southern Zones. There are two transitional zones — the Mediterranean-Sahara transition and the Sahel transition zone. The Saharan flora comprises around species of vascular plants. Approximately a quarter of these are endemic. About half of these species are common to the flora of the Arabian deserts. The central Sahara is estimated to include five hundred species of plants, which is extremely low considering the huge extent of the area.

Plants such as acacia trees, palms, succulents, spiny shrubs, and grasses have adapted to the arid conditions, by growing lower to avoid water loss by strong winds, by storing water in their thick stems to use it in dry periods, by having long roots that travel horizontally to reach the maximum area of water and to find any surface moisture, and by having small thick leaves or needles to prevent water loss by evapotranspiration. Plant leaves may dry out totally and then recover. Several species of fox live in the Sahara including: The addax , a large white antelope , can go nearly a year in the desert without drinking.

The dorcas gazelle is a north African gazelle that can also go for a long time without water. Other notable gazelles include the rhim gazelle and dama gazelle. There remain fewer than mature cheetahs, which are very cautious, fleeing any human presence. The cheetah avoids the sun from April to October, seeking the shelter of shrubs such as balanites and acacias.

They are unusually pale. However, it is currently extinct in the wild in Egypt and Libya.

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There are approximately mature individuals left in the wild. Other animals include the monitor lizards , hyrax , sand vipers , and small populations of African wild dog , [48] in perhaps only 14 countries [49] and red-necked ostrich. Other animals exist in the Sahara birds in particular such as African silverbill and black-faced firefinch , among others. There are also small desert crocodiles in Mauritania and the Ennedi Plateau of Chad. Its venom contains large amounts of agitoxin and scyllatoxin and is very dangerous; however, a sting from this scorpion rarely kills a healthy adult.

The Saharan silver ant is unique in that due to the extreme high temperatures of their habitat, and the threat of predators, the ants are active outside their nest for only about ten minutes per day. Dromedary camels and goats are the domesticated animals most commonly found in the Sahara.

Because of its qualities of endurance and speed, the dromedary is the favourite animal used by nomads. Human activities are more likely to affect the habitat in areas of permanent water oases or where water comes close to the surface. Here, the local pressure on natural resources can be intense. The remaining populations of large mammals have been greatly reduced by hunting for food and recreation.

In recent years development projects have started in the deserts of Algeria and Tunisia using irrigated water pumped from underground aquifers. These schemes often lead to soil degradation and salinization. People lived on the edge of the desert thousands of years ago [53] since the end of the last glacial period. The Sahara was then a much wetter place than it is today. Over 30, petroglyphs of river animals such as crocodiles [54] survive, with half found in the Tassili n'Ajjer in southeast Algeria.

Fossils of dinosaurs , [55] including Afrovenator , Jobaria and Ouranosaurus , have also been found here. The modern Sahara, though, is not lush in vegetation, except in the Nile Valley, at a few oases , and in the northern highlands, where Mediterranean plants such as the olive tree are found to grow. It was long believed that the region had been this way since about BCE, after shifts in the Earth's axis increased temperatures and decreased precipitation, which led to the abrupt desertification of North Africa about 5, years ago.

The Kiffian culture is a prehistoric industry, or domain, that existed between 10, and 8, years ago in the Sahara, during the Neolithic Subpluvial. Bones of many large savannah animals that were discovered in the same area suggest that they lived on the shores of a lake that was present during the Holocene Wet Phase, a period when the Sahara was verdant and wet. Gobero was discovered in during an archaeological expedition led by Paul Sereno , which sought dinosaur remains. Two distinct prehistoric cultures were discovered at the site: The Kiffians were a prehistoric people who preceded the Tenerians and vanished approximately years ago, when the desert became very dry.

The desiccation lasted until around BCE, when the earliest artefacts associated with the Tenerians have been dated to. Some skeletons have been discovered at Gobero. The Tenerians were considerably shorter in height and less robust than the earlier Kiffians. Craniometric analysis also indicates that they were osteologically distinct. The Kiffian skulls are akin to those of the Late Pleistocene Iberomaurusians , early Holocene Capsians , and mid-Holocene Mechta groups, whereas the Tenerian crania are more like those of Mediterranean groups.

The most interesting find is a triple burial, dated to years ago, of an adult female and two children, estimated through their teeth as being five and eight years old, hugging each other. Pollen residue indicates they were buried on a bed of flowers. The three are assumed to have died within 24 hours of each other, but as their skeletons hold no apparent trauma they did not die violently and they have been buried so elaborately — unlikely if they had died of a plague — the cause of their deaths is a mystery.

The Sahara: Facts, Climate and Animals of the Desert

Uan Muhuggiag appears to have been inhabited from at least the 6th millennium BCE to about BCE, although not necessarily continuously. The child was in a fetal position, then embalmed, then placed in a sack made of antelope skin, which was insulated by a layer of leaves. The specimen was determined to be that of a month old child of uncertain sex, who possessed Negroid features. A long incision on the specimen's abdominal wall also indicated that the body had been initially mummified by evisceration and later underwent natural desiccation.


The body was estimated to date from about BP. During the Neolithic Era, before the onset of desertification around BCE, the central Sudan had been a rich environment supporting a large population ranging across what is now barren desert, like the Wadi el-Qa'ab. By the 5th millennium BCE, the people who inhabited what is now called Nubia , were full participants in the "agricultural revolution", living a settled lifestyle with domesticated plants and animals. Saharan rock art of cattle and herdsmen suggests the presence of a cattle cult like those found in Sudan and other pastoral societies in Africa today.

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    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)
    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)
    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)
    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)
    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)
    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)
    Biographie dun désert: Le Sahara (French Edition) Biographie dun désert: Le Sahara (French Edition)

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