Namib Desertby Curtis Benjamin 03/11/2012 12:05:00 0 comments 4333 Views
The Namib is a coastal desert in southern Africa. The name Namib is of Nama origin and means "vast place". According to the broadest definition, the Namib stretches for more than 2,000 kilometres (1,200 mi) along the Atlantic coasts of Angola, Namibia, and South Africa, extending southward from the Carunjamba River in Angola, through Namibia and to the Olifants River in Western Cape, South Africa. The Namib's northernmost portion, which extends 450 kilometres (280 mi) from the Angola-Namibia border, is known as Moçâmedes Desert, while its southern portion approaches the neighboring Kalahari Desert. From the Atlantic coast eastward, the Namib gradually ascends in elevation, reaching up to 200 kilometres (120 mi) inland to the foot of the Great Escarpment. Annual precipitation ranges from 2 millimetres (0.079 in) in the most arid regions to 200 millimetres (7.9 in) at the escarpment, making the Namib the only true desert in southern Africa. Having endured arid or semi-arid conditions for roughly 55-80 million years, the Namib is also the oldest desert in the world.
The desert geology consists of sand seas near the coast, while gravel plains and scattered mountain outcrops occur further inland. The sand dunes, some of which are 300 metres (980 ft) high and span 32 kilometres (20 mi) long, are the second largest in the world after the Badain Jaran Desert dunes in China. Temperatures along the coast are stable and generally range between 9–20 °C (48–68 °F) annually, while temperatures further inland are variable—summer daytime temperatures can exceed 45 °C (113 °F) while nights can be freezing. Fogs that originate offshore from the collision of the cold Benguela Current and warm air from the Hadley Cell create a fog belt that frequently envelopes parts of the desert. Coastal regions can experience more than 180 days of thick fog a year. While this has proved a major hazard to ships—more than a thousand wrecks litter the Skeleton Coast—it is a vital source of moisture for desert life.
The Namib is almost completely uninhabited by humans except for several small settlements and indigenous pastoral groups, including the Ovahimba and Obatjimba Herero in the north, and the Topnaar Nama in the central region. Owing to its antiquity, the Namib may be home to more endemic species than any other desert in the world. Most of the desert wildlife is arthropods and other small animals that live on little water, although larger animals inhabit the northern regions. Near the coast, the cold ocean water is rich in fishery resources and supports populations of brown fur seals and shorebirds, which serve as prey for the Skeleton Coast's lions. Further inland, the Namib-Naukluft National Park, the largest game park in Africa, supports populations of African Bush Elephants, Mountain Zebras, and other large mammals. Although the outer Namib is largely barren of vegetation, lichens and succulents are found in coastal areas, while grasses, shrubs, and ephemeral plants thrive near the escarpment. A few types of trees are also able to survive the extremely arid climate.
Geography and geology
Gemsboks (Oryx gazella) are the biggest antelopes found in the Namib
The Namib Desert is one of the 500 distinct physiographic provinces of the South African Platform physiographic division. It occupies an area of around 80,950 km² (31,200 square miles), stretching from the Usiab River (north) to the town of Lüderitz (south) and from the Atlantic Ocean (west) to the Namib Escarpment (east). It is about 1,000 miles (1,600 km) long from north to south and its east-west width varies from 30 to 100 miles (50–160 km). To the north, the desert leads into the Kaokoveld; the dividing line between these two regions is roughly at the latitude of the city of Walvis Bay, and it consists in a narrow strip of land (about 50 km wide) that is the driest place in Southern Africa. To the south, the Namib borders on the South African Karoo semi-desert.
Southern Namib (between Lüderitz and the Kuiseb River) comprises a vast dune sea with some of the tallest and most spectacular dunes of the world, ranging in color from pink to vivid orange. In the Sossusvlei area, several dunes exceed 300 meters (984 ft) in height. The complexity and regularity of dune patterns in its dune sea have attracted the attention of geologists for decades, but it remains poorly understood.
Moving north from Sossusvlei, the sand gradually gives way to a rocky desert that extends all the way from Sossusvlei to the Swakop river. This area is traversed by the Tropic of Capricorn and it's mostly flat, although some scenic canyons and elevations are found in some areas, for example in the Moon Valley system. While most of the soil is rocky, sand dunes are still occasionally found in this region; for example, sand dunes occupy much of the coastline between Walvis Bay and Swakopmund.
The Namib desert is an important location for the mining of tungsten, salt and diamonds.
Several rivers and streams run through the Namib, although all of the rivers south of the Cunene River and north of the Orange River are ephemeral and rarely or never reach the ocean. These rivers arise in the interior mountains of Namibia and flow after summer rain storms.
The Namib's aridity is caused by the descent of dry air of the Hadley Cell, cooled by the cold Benguela current along the coast. It has less than 10 mm (0.4 inches) of rain annually and is almost completely barren. Besides rain being scarce, it is also hardly predictable. The western Namib gets less rain (5 mm) than the eastern Namib (85 mm). This is due to several factors. Winds coming from the Indian Ocean lose part of their humidity when passing the Drakensberg mountains, and are essentially dry when they reach the Namib Escarpment at the eastern end of the desert. Winds coming from the Atlantic Ocean, on the other hand, are pressed down by hot air from the east; their humidity thus forms clouds and fog. Morning fogs coming from the ocean and pushing inwards into the desert are a regular phenomenon along the coast, and much of the life cycle of animals and plants in the Namib relies on these fogs as the main source of water.
The dry climate of the Namib reflects the almost complete lack of bodies of water on the surface. Most rivers flow underground and/or are dry for most of the year, and even when they are not, they usually drain into endorheic basins, without reaching the sea. The Swakop and the Omaruru are the only rivers that occasionally drain into the ocean.
All along the coast, but mostly in the northernmost part of it, interaction between the water-laden air coming from the sea via southerly winds, some of the strongest of any coastal desert, and the dry air of the desert causes immense fogs and strong currents. It causes sailors to lose their way; this is testified by the remnants of a number of shipwrecks that can be found along the Skeleton Coast, in northern Namib. Some of these wrecked ships can be found as much as 50 metres (55 yds) inland, as the desert slowly moves westwards into the sea, reclaiming land over a period of many years. Benguela's El Nino (similar to the Pacific event in its environmental change in the seas) spreads from the Kunene estuary southward to, on occasion, south of Luderitz. Warm waters with depth and associated water flows from northwesterly direction were first fully catalogued by Sea Fisheries researchers, Cape Town (L V Shannon et al.). The research noted the positive effect of Benguela\'s El Nino on the rainfall of the interior. Rainfall records also show positive values variously across the Namib, Desert Research Station, Gobabeb for instance. This event recurs approximately mid-decade (1974, 1976, 1994, 1995 and 2006 are recent examples)
Animals and plants
A number of unusual species of plants and animals are found in this desert, many of which are endemic and highly adapted to the specific climate of the area. One of the most well-known endemic plants of the Namib is the bizarre Welwitschia mirabilis; a shrub-like plant, it grows two long strap-shaped leaves continuously throughout its lifetime. These leaves may be several meters long, gnarled and twisted from the desert winds. The taproot of the plant develops into a flat, concave disc in age. Welwitschia is notable for its survival in the extremely arid conditions in the Namib, mostly deriving moisture from the coastal sea fogs. An area where Welwitschias are a common sight is found in the surroundings of the Moon Valley, including the eponymous Welwitschia Plains.
The Namib fauna mostly comprises arthropods and other small animals that can live on little water, but a few species of bigger animals are also found, including antelopes and gazelles (such as oryxes and springboks), ostrichs, and in some areas even desert elephants. All these species have developed techniques to survive in the Namib environment. A number of endemic darkling beetles species- such as the Namib Desert beetle- have bumpy elytrons with a pattern of hydrophilic bumps and hydrophobic troughs. These cause humidity from the morning fogs to condensate into droplets, which roll down the beetle's back to its mouth; they are collectively known as "fog beetles". Another beetle, the Lepidochora discoidalis, builds "water-capturing" webs. Black-backed jackals lick humidity from stones. Gemsboks (also known as Oryxes) can raise the temperature of their bodies to 40 °C in the hottest hours of the day. The desert is also home to meerkats and several species of lizards.
In 1934 it was observed that lions were common in the coastal regions, mountains, and ephemeral rivers, between the lower Kuiseb River and the Kunene River.
Although the desert is largely unpopulated and inaccessible, there are year-round settlements at Sesriem, close to the famous Sossusvlei area, and other small outposts in other locations. Namibe in Angola, and Lüderitz, Walvis Bay and Swakopmund in Namibia, bordering on the desert, are the main settlements in the area.
Namib-Naukluft National Park
The Namib-Naukluft National Park, that extends over a large part of the Namib Desert, is the largest game reserve in Africa and one of the largest of the world. While most of the park is hardly accessible, several well-known visitor attractions are found in the desert. The prominent attraction is the famous Sossusvlei area, where high orange sand dunes surround vivid white salt pans, creating a fascinating landscape.
Access to the park is either by gravel roads or dust roads (except for 60 km of concrete road from the Sesriem gate to Sossusvlei) or by light aircraft from Windhoek (the capital of Namibia, about 480 km (300 mi) north-east of the centre of the desert), or Swakopmund and Walvis Bay at the north end of the desert.