Waterfalls are classified by how the water leaves the rock and how it lands. The main types are plunge (water falls free of the cliff, like Angel Falls in Venezuela), horsetail (water keeps touching the rock as it falls), block or curtain (a wide river drops as one sheet, like Victoria Falls), segmented (the flow splits into separate streams, like Iguazu Falls), tiered (a series of distinct drops, like Yosemite Falls), punchbowl (a narrow chute shoots into a wide pool) and cascade (water tumbles down a staircase of small steps). Fuller classifications add the ledge, the fan, the chute, the cataract and the moulin, a waterfall inside a glacier. Many real falls combine two or three types. The quickest way to understand them is to look at the places that define each one.
Angel Falls, Venezuela: the plunge in its purest form
A plunge waterfall is one where the water loses contact with the rock face and falls through open air. Angel Falls, known in the Pemon language as Körepakupai Vená, is the textbook case. It pours off the rim of Auyán-tepui, a flat-topped table mountain in Canaima National Park in Bolívar State, and its uninterrupted drop is 807 metres (2,648 ft). The full height usually quoted, 979 metres (3,212 ft), adds about 400 metres of sloping cascades and rapids below the main fall and a final 30-metre plunge, so even the world's tallest waterfall is technically a combination type.
A plunge forms where a stream runs to the edge of a sheer cliff with nothing below the lip to deflect it. On a tepui the stream crosses the summit plateau and simply runs out of mountain. Over such a long fall, much of the water breaks into mist before it reaches the base, and in the dry season the stream can thin to a white thread that frays into spray. The falls take their English name from Jimmie Angel, a US aviator who first flew over them on 16 November 1933. Whether Angel Falls or South Africa's Tugela Falls is actually taller has never been settled by a new survey, because both were measured from a considerable distance.
Horsetail Falls and Punch Bowl Falls: two Oregon falls that show their types
Two waterfalls in the Columbia River Gorge, both in Multnomah County, Oregon, carry the names of waterfall types and show them clearly. Horsetail Falls, on Horsetail Creek beside the Historic Columbia River Highway, drops over a rounded face of columnar basalt. Because the rock bulges outward, the water stays in contact with it for most of the descent and fans into a shape like a horse's tail. That is the defining feature of a horsetail fall: the water slides down the rock rather than leaping clear of it, as a plunge does.
Punch Bowl Falls, on Eagle Creek, is small at 11 metres (35 ft) tall and 3 metres (10 ft) wide, but it is the waterfall credited with giving the punchbowl type its name. Eagle Creek squeezes through a narrow notch in the basalt and shoots out into a wide, almost circular pool ringed by mossy walls. A punchbowl needs both parts: a tight constriction that concentrates the flow, and a broad basin below that the falling water has scoured out. In 2017 the cliff on the left side of the creek collapsed between Punch Bowl and Lower Punch Bowl Falls, and the debris changed the stream's course between the two drops, a reminder that these shapes keep changing.
Victoria Falls: a block waterfall dropping into a basalt fracture
A block, sheet or curtain waterfall is one where a wide river goes over the edge as a single front of water. Victoria Falls on the Zambezi, on the border between Zambia and Zimbabwe, is the largest example. It is 1,708 metres (5,604 ft) wide and up to 108 metres (354 ft) high, which together make it the world's largest single sheet of falling water. The Lozi name, Mosi-oa-Tunya, means "the smoke that thunders", after the spray that rises more than 400 metres and can be seen from up to 50 kilometres away.
The geology explains the shape. Upstream, the Zambezi flows across a flat sheet of basalt. At the falls, the entire width of the river drops into the First Gorge, a straight chasm that follows a fracture zone in that basalt. The only exit from the chasm is a gap about 110 metres wide, which sends the river into a zigzag series of gorges, from the Second Gorge spanned by the Victoria Falls Bridge to the Songwe Gorge, 140 metres deep.
Victoria Falls also shows that a waterfall's type can change with the seasons. The Zambezi floods from February to May, peaking in April, when the curtain is unbroken and the spray hides the foot of the falls. Between September and January, islands on the crest widen and up to half the rock face can run dry, splitting the curtain into separate streams such as the Devil's Cataract, Main Falls, Rainbow Falls and Eastern Cataract. In the dry months, then, it behaves more like a segmented fall.
Iguazu Falls: a segmented waterfall split by islands
A segmented waterfall is one where the river reaches the edge as several distinct streams. Iguazu Falls, on the Iguazu River between the Argentine province of Misiones and the Brazilian state of Paraná, is the largest waterfall system in the world. Its edge runs for 2.7 kilometres, and islands along it split the river into between 150 and 300 separate falls depending on the water level, often given as roughly 275. About half the river pours into the Devil's Throat (Garganta del Diablo), a chasm 80 to 90 metres wide.
The falls are also a two-step staircase. Three layers of basalt from the Serra Geral formation create steps of 35 and 40 metres, and the hard, bubble-filled basalt at the top of each layer controls where the edge sits. Individual falls range from 60 to 82 metres high. Average flow is about 1,746 m³/s, and the record was 45,700 m³/s on 9 June 2014. The greatest volume of water usually pours over between December and February, one of the wettest periods in this humid subtropical region.
Yosemite Falls: a tiered drop from a hanging valley
A tiered waterfall descends in a series of separate drops, each with its own base. Yosemite Falls in California's Sierra Nevada falls a total of 739 metres (2,425 ft) in three sections. Upper Yosemite Fall is a 440-metre (1,430 ft) plunge, more than half the total. Below it, four smaller drops known as the Middle Cascades add 206 metres (675 ft) in a narrow gorge most viewpoints never show, and Lower Yosemite Fall finishes with 98 metres (320 ft) before Yosemite Creek joins the Merced River.
The origin is glacial. Yosemite Creek flows across Eagle Creek Meadow in a hanging valley, a side valley left high above the main Yosemite Valley after glaciers deepened the main valley far more than its tributaries. The other large falls of Yosemite Valley formed the same way. Many are also seasonal: Yosemite Falls peaks in late spring with snowmelt, and in all but the wettest years it stops flowing in late summer or autumn. Nearby, Horsetail Fall on El Capitan runs only in winter and early spring.
Plitvice Lakes, Croatia: cascades that build their own steps
A cascade is water tumbling down a series of small rock steps rather than one big drop. Most cascades form where a stream crosses broken or layered rock, but at Plitvice Lakes National Park in Croatia, a UNESCO World Heritage Site since 1979, the steps build themselves. The water is rich in dissolved calcium carbonate from the surrounding karst. As it flows it deposits tufa, also called travertine, and those deposits grow into natural dams. Sixteen lakes are visible at the surface, stepped one above another and linked by cascades.
The barriers grow by up to 13 millimetres a year, faster than the water wears them away, so Plitvice runs the opposite way from most waterfalls. About 400 years ago, Lake Kozjak was two lakes: a faster-growing barrier downstream drowned a 40-metre tufa wall that had once formed a waterfall. Elsewhere in the park, Veliki slap ("Big Waterfall"), falls 78 metres (256 ft) on the Plitvica stream.
Niagara's Horseshoe Falls: how a caprock waterfall moves upstream
Niagara's Horseshoe Falls shows the process behind many plunge and block waterfalls: the caprock model. On the Canadian side of the Niagara River, the falls are about 57 metres (187 ft) high and 790 metres wide. The lip is hard limestone and dolomite of the Lockport Formation. Below it lies the softer shale of the Rochester Formation. Spray and turbulence wear away the shale, the dolomite above is left overhanging, and eventually blocks of caprock break off into the plunge pool. Each collapse moves the edge a little further upstream.
About 10,900 years ago the falls stood near present-day Queenston, Ontario, and Lewiston, New York. Since then they have cut back roughly 10.9 kilometres, leaving the Niagara Gorge behind them. Over at least the last 560 years the falls retreated an average of 1 to 1.5 metres a year. Today, after engineering works including underwater weirs and a strengthened crest, the rate is about 30 centimetres a year. Iguazu's basalt edge retreats more slowly, at an estimated 1.4 to 2.1 centimetres a year, which shows how much the type of rock under the lip controls a waterfall's shape and life.
Every type above comes back to the same few variables: how hard the rock at the lip is, how wide the river is when it arrives, whether a glacier or a fault left a step in the land, and how much the flow changes through the year. For the erosion process in more detail, see how waterfalls are formed. The individual guides to Angel Falls and the waterfalls of Plitvice cover two of the clearest examples, and the Iguazu Falls guide follows the world's largest segmented falls from the Devil's Throat to the Paraná.