VICTORIA FALLS

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

 Introduction

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 a height of an average of 100 m (360 ft), forming the largest sheet of falling water in the world. The falls' maximum flow rate compares well with that of other major waterfalls.
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 slot-like chasm, connected to a long series of gorges.
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. 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 O' Tonya 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, escarpment, or deep valleys which might be expected to create a waterfall, only flat plateau extending hundreds of kilometers 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 Batoka gorges.
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):Devil's Cataract, Main Falls, Rainbow Falls (the highest) and the Eastern Cataract.

Flood and dry season flow rates

High season:

The higest flow each year is recorded at the end of April. The river's high water can be considered from February to June. During this perios, 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 "lunaraimbow" 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.

Dry season:

The lowest flow each year is recorded at the beginning of November. 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. The minimum flow is around a tenth of the April figure; this variation in flow is greater than that of other major falls. At lowest flow, the Zambian side of the Victoria Falls being higher than the Zimbabwean side, the water goes toward Zimbabwe and the Zambian side become dry rock wall. during this time of the year (October/November), if you are staying on the Zambian side, the falls are best seen by air or from the Zimbabwean side.

The best time to see Victoria Falls depends on what one wants to see. July/August and January/February offers the best compromise between a flow rate which impresses with its power, and the falls not being completely obscured by spray.
Victoria Falls are roughly twice the height of North America's Niagara Falls and well over twice the width of its Horse shoe falls. In height and width Victoria Falls is rivalled only by South America's Iguazu Falls. See table for comparisons.

How the Victoria Falls formed

The recent geological history of Victoria Falls can be seen in the form of the gorges below the falls. The basalt plateau over which the Upper Zambezi flows has many large cracks filled with weaker sandstone. In the area of the current falls the largest cracks run roughly east to west (some run nearly north-east to south-west), with smaller north-south cracks connecting them.
Over at least 100,000 years, the falls have been receding upstream through the Batoka gorges, eroding the sandstone-filled cracks to form the gorges. The river's course in the current vicinity of the falls is north to south, so it opens up the large east-west cracks across its full width, then it cuts back through a short north-south crack to the next east-west one. The river has fallen in different eras into different chasms which now form a series of sharply zig-zagging gorges downstream from the falls.
Ignoring some dry sections, the Second to Fifth and the Songwe Gorges each represents a past site of the falls at a time when they fell into one long straight chasm as they do now. Their sizes indicate that we are not living in the age of the widest ever Mosi-oa-Tunya.
The falls has already started cutting back the next major gorge, at the dip in one side of the 'Devil's cataract's section of the falls. This is not actually a north-south crack, but a large east-north-east line of weakness across the river, and that is where the next full width falls will eventually form.

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