Chad - Geography
The geographical center of the African continent is not an Alpine range, as in Europe and Asia, but on the contrary a deep depression largely flooded by marsh waters, and in its relief inclining rather towards the Niger and the western regions. East and south this basin is encircled by mountains and uplands, north and went by disconnected hills and terraces, falling in the south-west to open, low-lying plains, through which the great lacustrine depression almost merges in the Benue hydi>ographic systom. Thus the central region is almost everywhere easily accessible.
Chad is a landlocked country in north central Africa, with a territory twice the size of Texas. Population densities range from 54 persons per square kilometer in southern zones to 0.1 persons in the vast northern desert region, itself larger than France. The population of the capital city of N'Djamena, situated at the confluence of the Chari and Logone Rivers, is representative of Chad’s ethnic and cultural diversity.
Chad has four bioclimatic zones. The northernmost Saharan Desert zone averages less than 200 mm (8") of rainfall annually. The central Sahelian zone receives between 200 and 600 mm (24") of rainfall and has vegetation ranging from grass/shrub steppe to thorny, open savanna. The southern zone, often referred to as the Sudanian zone, receives between 600 and 1,000 mm (39"), with woodland savanna and deciduous forests for vegetation. Rainfall in the small Guinea zone, limited to Chad's southwestern tip, ranges between 1,000 and 1,200 mm (47").
The country's topography is generally flat, with the elevation gradually rising as one moves north and east away from Lake Chad. The highest point in Chad is Emi Koussi, a mountain that rises 3,100 meters (10,200 ft.) in the northern Tibesti Mountains. The Ennedi Plateau and the Ouaddai highlands in the east complete the image of a gradually sloping basin, which descends toward Lake Chad. There also are central highlands in the Guera region rising to 1,500 meters (4,900 ft.).
Lake Chad, one of the most important wetlands on the continent and home to hundreds of species of fish and birds, shrank dramatically over 4 decades due to increased water use and inadequate rainfall. The lake, the second-largest in West Africa, covered 25,000 square kilometers in 1963 but had decreased to 1,350 square kilometers as of 2002. The Chari and Logone Rivers, both of which originate in the Central African Republic and flow northward, provide most of the water entering Lake Chad.
Landlocked in Africa's center, Chad has been simultaneously at the core of the region's evolution and in a zone dividing two geographic areas and cultural heritages. On the one hand, a great inland sea, of which Lake Chad is but a remnant, once supported a diversity of animal life and vegetation. In ancient times, people speaking three of Africa's four major language groups lived near its shores; some migrated to other regions of the continent while others remained. In more recent times, Chad has become a transition zone dividing the arid north from the tropical south.
This geographic division coincides with social and cultural dichotomies. As a result of years of voluntary or forced migrations, the people of Chad speak more than 100 distinct languages and comprise many different ethnic groups. Such diversity has enriched Chad's culture, permitting the admixture of traditions and life-styles. At the same time, it has promoted inter- and intraethnic strife, resulting in levels of violence ranging from clan feuds to full-scale civil war. Factionalism has become a keynote of Chad's recent history and has unquestionably impeded nation building.
Because of the area's centrality, Chad's history has been heavily influenced by the influx of foreigners. Some came for economic reasons, for example, to travel the trans-Saharan trade routes or to search for natural resources. Others came teaching the religion of Muhammad or of Christ. But some had more nefarious goals and invaded the region to capture slaves or to plunder weaker states.
The Lake Chad catchment has an area 2,500,000 km2. In the past it contained a giant lake known as Lake Megachad — on the borders of Nigeria, Chad, Cameroon and Niger. At its peak around 6,000 years ago, Palaeolake Mega-Chad was the largest freshwater lake on Earth, with an area of 360,000 km2. Now today's Lake Chad is reduced to a fraction of that size, at only 355 km2. The humid period ended abruptly 5,000 years ago, indicating that the African monsoon exhibits a nonlinear response to insolation forcing. It took the southern Sahara just a couple of hundred years to dry out completely.
The last long-lived Lake Megachad high stand occurred during the early and middle Holocene, with a shoreline at an altitude of about 329m and a lake area of 361,000 km2. In its heyday it was fed by a number of large river systems that rose in the Ahagar, Tassili, Air, Tibesti and Edeni mountains of what is now the Sahara Desert. The river in the southern part of the catchment, the Komadugu, Chari and Longwe, still contains significant flow today and feeds the (much smaller) modern day Lake Chad.
Lake shoreline landforms were discovered in the Chad Basin early last century when the existence of giant palaeolake Megachad was first postulated and described as an African Caspian Sea. Further investigation of the archaeology and sedimentology of the ridges (Thiemeyer 1992) led to the resurrection of the megalake theory, and these results were supported by interpretation of the topography of the Chad Basin. The shoreline elevations suggest that its peak the palaeolake Megachad had an area of at least four hundred thousand square kilometers, bigger than the Caspian Sea, the biggest lake on Earth today.
For many years, Earth scientists theorized that the remains of Lake Mega-Chad provided the fertilizer for the Amazonian rainforest, thousands of miles away in South America. Without a constant infusion of nutrients - windblown dust - the lush vegetation would disappear because nutrients are washed away by the constant rainfall. When the lake shrank, it left behind thousands of years of silt deposits (which dried up and formed sand dunes) which has been carried by the wind, all the way to South America.
Located in North-Eastern Chad, in a hot and hyperarid desert setting with less than 2mm rainfall per year, the Lakes of Ounianga comprises a total of 18 lakes, in two groups, displaying a variety of sizes, depths, colorations and chemical compositions. The property covers 62,808 ha and has a 4,869 ha buffer zone. The Lakes of Ounianga property is located in a basin which, less than 10,000 years ago, was occupied by a much larger lake and has a globally unique hydrological system, sustaining the largest permanent freshwater lakes system in the heart of a hyperarid environment. The property also displays a range of striking aesthetic features, with varied coloration associated with the different lakes and their vegetation, and the presence of dramatic natural desert landforms that all contribute to the exceptional natural beauty of the landscape of the property. The shape and distribution of the lakes, combined with the effect of the wind moving the floating vegetation in the lakes, gives the impression of “waves of water flowing in the desert”.
The aesthetic beauty of the site results from a landscape mosaic which includes the varied coloured lakes with their blue, green and /or reddish waters, in reflection of their chemical composition, surrounded by palms, dunes and spectacular sandstone landforms, all of it in the heart of a desert that stretches over thousands of kilometres. In addition, about one third of the surface of the Ounianga Serir Lakes is covered with floating reed carpets whose intense green colour contrasts with the blue open waters.
Aorounga Impact Crater is located in the Sahara Desert, in north-central Chad, and is one of the best-preserved impact structures in the world. The crater is thought to be middle or upper Devonian to lower Mississippian (approximately 345–370 million years old) based on the age of the sedimentary rocks deformed by the impact. Spaceborne Imaging Radar (SIR) data collected in 1994 suggests that Aorounga is one of a set of three craters formed by the same impact event. The other two suggested impact structures are buried by sand deposits.
The concentric ring structure of the Aorounga crater—renamed Aorounga South in the multiple-crater interpretation of SIR data—is clearly visible in this detailed astronaut photograph. The central highland, or peak, of the crater is surrounded by a small sand-filled trough; this in turn is surrounded by a larger circular trough. Linear rock ridges alternating with light orange sand deposits cross the image from upper left to lower right; these are called yardangs by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the northeast at Aorounga, and sand dunes formed between the yardangs are actively migrating to the southwest.
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