Victoria Falls’s Size
While it is neither the highest nor the widest waterfall in the world, Victoria Falls is classified as the largest, based on its combined width of 1,708 metres (5,604 ft) and height of 108 metres (354 ft), resulting in the world's largest sheet of falling water. Victoria Falls is 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 Argentina and Brazil's Iguazu Falls. For a considerable distance upstream from 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; only a 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 transverse chasm 1,708 metres (5,604 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 metres (260 ft) at its western end to 108 metres (354 ft) in the centre. The only outlet to the First Gorge is a 110-metre (360 ft) wide gap about two-thirds of the way across the width of the falls from the western end. The whole volume of the river pours into the Victoria Falls gorges from this narrow cleft. 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—the point from which Livingstone first viewed the falls. 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. The Zambezi river, upstream from 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 48 km (30 mi) 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.
Gorges
The entire volume of the Zambezi River pours through the First Gorge's 110 metres (360 ft) wide exit for a distance of about 150 metres (490 ft), then enters a zigzagging series of gorges designated by the order in which the river reaches them. Water entering the Second Gorge makes a sharp right turn and has carved out a deep pool there called the Boiling Pot. Reached via a steep footpath from the Zambian side, it is about 150 metres (500 ft) across. Its surface is smooth at low water, but at high water is marked by enormous, slow swirls and heavy boiling turbulence. Objects and humans that are swept over the falls, including the occasional hippopotamus or crocodile, are frequently found swirling about here or washed up at the north-east end of the Second Gorge. This is where the bodies of Mrs Moss and Mr Orchard, mutilated by crocodiles, were found in 1910 after two canoes were capsized by a hippo at Long Island above the falls. The principal gorges are: • First Gorge: the one the river falls into at Victoria Falls • Second Gorge: 250 metres (820 ft) south of falls, 2.15 kilometres (1.34 mi) long, spanned by the Victoria Falls Bridge • Third Gorge: 600 metres (2,000 ft) south, 1.95 kilometres (1.21 mi) long, containing the Victoria Falls Power Station • Fourth Gorge: 1.15 kilometres (0.71 mi) south, 2.25 kilometres (1.40 mi) long • Fifth Gorge: 2.25 kilometres (1.40 mi) south, 3.2 kilometres (2.0 mi) long • Songwe Gorge: 5.3 kilometres (3.3 mi) south, 3.3 kilometres (2.1 mi) long named after the small Songwe River coming from the north-east, and the deepest at 140 metres (460 ft), the level of the river in them varies by up to 20 metres (66 ft) between wet and dry seasons.
Victoria Falls Formation
The Upper Zambezi River originally drained south through present day Botswana to join the Limpopo River. A general uplift of the land between Zimbabwe and The Kalahari desert about 2 million years ago blocked this drainage route, and a large paleo lake known as Lake Makgadikgadi formed between the Kalahari and the Batoka Basaltic Plateau of Zimbabwe and Zambia. This lake was originally endorheic and had no natural outlet, Under wetter climate conditions about 20,000 years BP, it eventually overflowed and began to drain to the east cutting the Batoka Gorge through the basalt as it went. The recent geological history of Victoria Falls can be seen in the overall form of the Batoka Gorge, with its six individual gorges and eight past positions of the falls. The east-west oriented gorges imply structural control with alignment along joints of shatter zones, or faults with 50 metres (160 ft) of vertical displacement as is the case of the second and fifth gorges. Headward erosion along these structural lines of weakness would establish a new fall line and abandonment of the earlier line. North-south oriented joints control the south flowing sections of the river. One of these is the "Boiling Pot", which links the First Gorge with the Second Gorge. The falls may have already started cutting back the next major gorge, at the dip in one side of the "Devil's Cataract", between the western river bank and Cataract Island. The lip in the current falls is lowest here and carries the greatest concentration of water at flood stage. The sedimentary sequence overlying the basalt at the Zambezi River margins is called the Victoria Falls Formation, which consists of gravel, the Pipe sandstone, Kalahari Sands, and aeolian sand and alluvium. A 15–45 m scarp bounds the river about 5–6 km from the main channel, and a series of river terraces are evident between the scarp and the channel. Source: Wikipedia 
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