Wednesday, March 26, 2008

Victoria Falls or Mosi-oa-Tunya (the Smoke that Thunders)

The Victoria Falls or Mosi-oa-Tunya (the Smoke that Thunders) is a waterfall situated in southern Africa between the countries of Zambia and Zimbabwe. The falls are, by some measures, the largest waterfall in the world, as well as being among the most unusual in form, and having arguably the most diverse and easily-seen wildlife of any major waterfall site.

Mosi-oa-Tunya is the name used by the local people and Victoria Falls is the later name given by Europeans (see pre-colonial history, below).

Although Victoria Falls constitute neither the highest nor the widest waterfall in the world, their claim to be the largest is based on a width of 1.7 km (1 mile) and height of 108 m (360 ft), forming the largest sheet of falling water in the world.


The unusual form of Victoria Falls enables virtually the whole width of the falls to be viewed face-on, at the same level as the top, from as close as 60 m (200 ft), because the whole Zambezi River drops into a deep, narrow slotlike chasm, connected to a long series of gorges. Few other waterfalls allow such a close approach on foot. Many of Africa's animals and birds can be seen in the immediate vicinity of Victoria Falls, and the continent's range of river fish is also well represented in the Zambezi, enabling wildlife viewing and sport fishing to be combined with sightseeing. Victoria Falls are one of Africa's major tourist attractions, and are a UNESCO World Heritage Site (see box below). The falls are shared between Zambia and Zimbabwe, and each country has a national park to protect them and a town serving as a tourism centre: Mosi-oa-Tunya National Park and Livingstone in Zambia, and Victoria Falls National Park and the town of Victoria Falls in Zimbabwe.

Physical Features: For a considerable distance above the falls, the Zambezi flows over a level sheet of basalt, in a shallow valley bounded by low and distant sandstone hills. The river's course is dotted with numerous tree-covered islands, which increase in number as the river approaches the falls. There are no mountains, escarpments, or deep valleys which might be expected to create a waterfall, only flat plateau extending hundreds of kilometres in all directions. The falls are formed as the full width of the river plummets in a single vertical drop into a chasm 60–120 m (200–400 ft) wide, carved by its waters along a fracture zone in the basalt plateau. The depth of the chasm, called the First Gorge, varies from 80 m (262 ft) at its western end to 108 m (360 ft) in the centre. The only outlet to the First Gorge is a 110 m (360 ft) wide gap about two-thirds of the way across the width of the falls from the western end, through which the whole volume of the river pours into the Victoria Falls gorges.

Flood And Dry Season Flow Rates: There are two islands on the crest of the falls that are large enough to divide the curtain of water even at full flood: Boaruka Island (or Cataract Island) near the western bank, and Livingstone Island near the middle. At less than full flood, additional islets divide the curtain of water into separate parallel streams. The main streams are named, in order from Zimbabwe (west) to Zambia (east): Leaping Water (called Devil's Cataract by some), Main Falls, Rainbow Falls (the highest) and the Eastern Cataract. The Zambezi basin above the falls experiences a rainy season from late November to early April, and a dry season the rest of the year. The river's annual flood season is February to May with a peak in April, The spray from the falls typically rises to a height of over 400 metres (1,300 ft), and sometimes even twice as high, and is visible from up to 50 km (30 miles) away. At full moon, a "moonbow" can be seen in the spray instead of the usual daylight rainbow. During the flood season, however, it is impossible to see the foot of the falls and most of its face, and the walks along the cliff opposite it are in a constant shower and shrouded in mist. Close to the edge of the cliff, spray shoots upward like inverted rain, especially at Zambia's Knife-Edge Bridge.

As the dry season takes effect, the islets on the crest become wider and more numerous, and in September to January up to half of the rocky face of the falls may become dry and the bottom of the First Gorge can be seen along most of its length. At this time it becomes possible (though not necessarily safe) to walk across some stretches of the river at the crest. It is also possible to walk to the bottom of the First Gorge at the Zimbabwean side. The minimum flow, which occurs in November, is around a tenth of the April figure; this variation in flow is greater than that of other major falls, and causes Victoria Falls' annual average flow rate to be lower than might be expected based on the maximum flow. Victoria Falls are roughly twice the height of North America's Niagara Falls and well over twice the width of its Horseshoe Falls. In height and width Victoria Falls is rivalled only by South America's Iguazu Falls.

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