Victoria Falls

Long, long ago, hot melted rock flowed out and cooled into hard, dark rock.

The rock has long cracks in it. The river wore one crack deep and wide, and now it falls into it. Bit by bit, the falls move back up the river.

The rock at Victoria Falls is basalt, a hard, dark rock made from ancient lava flows. Long cracks called joints run through it. Just above the falls, the Zambezi bends to flow south, and the whole river plunges into a deep, narrow slot worn out along one of these cracks. That slot is the chasm the falls drop into today.

Below the falls, the river zigzags through a series of steep gorges, turning from one crack to the next. UNESCO says seven earlier waterfalls once stood in seven of them. The falling water slowly wears away the bottom of the cliff until the rock above gives way, so the falls creep upstream. The Devil's Cataract, on the Zimbabwe side, is where the next cut has begun.

The falls cross banded basalt from ancient lava flows, with Kalahari sandstones and chalcedony; UNESCO notes that, unlike the vertical columns of the Giant's Causeway, these basalts are layered. Geologists writing in GEO ExPro identify the rock as the Batoka Basalt, part of the Karoo large igneous province of about 180 million years ago, creased by families of roughly east-west joints. Just upstream the Zambezi bends south and plunges 108 m into a chasm less than 120 m wide, carved along one of those joints.

IUCN's 1989 evaluation for UNESCO says that since the uplift of the Makgadikgadi Pan area some two million years ago, the Zambezi has been cutting through the basalt, exploiting weak fissures and forming a series of retreating gorges. The plunging water undercuts the base of the falls until the cliff collapses, so the falls migrate upstream. UNESCO calls the gorges an outstanding example of river capture: eight steep-sided gorges zigzag for about 150 km, seven previous waterfalls occupied the seven gorges below the present falls, and the Devil's Cataract is the starting point for cutting back to a new waterfall.

The spray from the falls is like rain that never stops.

So a small green forest grows right next to the falls. Monkeys, birds and warthogs live there. Special birds build nests in the steep gorges.

The cloud of spray from the falls can rise about 500 meters high. It drifts down like rain on the land beside the waterfall, keeping it wet all year. Because of this, a narrow strip of rainforest grows there, full of vines and trees.

Visitors on the Zimbabwe side may see warthogs, vervet monkeys, baboons and birds such as the bright Livingstone's turaco and the trumpeter hornbill. The flame lily, Zimbabwe's national flower, grows here too. The steep gorges below the falls are nesting places for endangered birds, including the Taita falcon and the black eagle.

UNESCO describes a riverine rainforest within the splash zone: a fragile, discontinuous forest on sandy alluvium that depends on abundant water and the high humidity of a spray plume up to about 500 m tall.

The eight gorges and the islands in the core zone are breeding sites for four endangered and migratory bird species, among them the Taita falcon and the black eagle, and the property is an Important Bird Area. National Geographic notes that a fence keeps most large animals out of the main viewing area in Zimbabwe, but warthogs, vervet monkeys, baboons, Livingstone's turaco and trumpeter hornbills are often seen, with vines, mahogany trees and the flame lily along the path. UNESCO also records stone tools from early humans and hunter-gatherers in the area.

Some months, the river is full and the falls roar.

Other months, there is less water. Then you can see the dark rock wall. Rainbows shine in the spray on sunny days.

How the falls look depends on the season. From March to May the Zambezi is at its fullest, after the summer rains, and the spray can be so thick it is hard to see the falls at all. From September to November, the hot, dry season, there is much less water, and you can see the rock walls of the gorge.

Rainbows often appear in the spray, especially in the middle of the morning and the middle of the afternoon. On some nights near the full moon, visitors can even see a moonbow, a rainbow made by moonlight.

National Geographic describes the cycle: the falls are at their high-water peak in the southern autumn (March to May), still flowing strongly but with less spray in winter (June to August), at their lowest in the hot, dry spring (September to November), when the geology of the gorge is easiest to see, and refilling with the summer rains from December.

UNESCO says the spray can be seen 30 km away from the Lusaka road in Zambia and 50 km away from the Bulawayo road in Zimbabwe. Rainbows are common in mid-morning and mid-afternoon, and around the full moon the Zimbabwe park reopens in the evening for lunar rainbows, which form when moonlight is refracted through the spray, depending on the weather and the spray.