Angel Falls in Venezuela is usually named the tallest waterfall on Earth. Its water drops 979 metres, and 807 metres of that is one unbroken plunge. A waterfall forms wherever a river or stream flows over a steep drop, usually where hard rock sits on top of softer rock that wears away faster. Victoria Falls in southern Africa makes the biggest single curtain of falling water, 1,708 metres wide. Iguazu Falls, on the border of Argentina and Brazil, splits into between about 150 and 300 separate falls. The Boyoma Falls in the Democratic Republic of the Congo carry more water each year than any other waterfall. Waterfalls come in types such as plunge, horsetail, cascade and tiered. Some freeze solid in winter, and some even have birds nesting behind the spray.
Hard Rock on Top, Soft Rock Below: How Niagara Falls Formed
Most big waterfalls start with a rock sandwich. A layer of hard rock sits on top of a layer of softer rock. The river flows across the hard layer and wears it down only slowly. Where the river reaches the edge, it tumbles onto the soft rock below. That soft layer wears away much faster.
Splashing water digs out the soft rock under the edge. Soon the hard top layer sticks out like a diving board, with nothing holding it up. In the end it snaps off and crashes down. The broken blocks swirl around at the bottom and grind out a deep hole called a plunge pool. Then the whole thing happens again. Each time, the edge of the waterfall moves a little bit upstream.
Niagara Falls, on the border between Canada and the United States, is the perfect example. Its top layer is hard limestone and dolomite. Under it lies soft shale. The falls began forming at the end of the last ice age, when melting glaciers filled the Great Lakes. The Niagara River then spilled over a long cliff called the Niagara Escarpment.
About 10,900 years ago, the falls stood near the towns of Queenston, Ontario, and Lewiston, New York. Since then they have crept about 10.9 kilometres upstream. That trail of retreat left behind the long Niagara Gorge. For at least 560 years, the falls moved back about 1 to 1.5 metres every year. Engineers have since slowed that to about 30 centimetres a year. They built underwater walls to steer the strongest currents and strengthened the top of the falls. In 1969 they even switched off the American Falls for several months with a temporary dam, so they could study and bolt the rock.
At today’s speed, Niagara would need about 50,000 years to wear its way back the last 32 kilometres to Lake Erie. Then the falls would disappear.
Angel Falls and Tugela Falls: The Tallest Drops on Earth
Angel Falls pours off the edge of Auyán-tepui, a flat-topped mountain in Canaima National Park in Venezuela. The park is a UNESCO World Heritage Site. The total height of 979 metres includes the giant plunge plus about 400 metres of sloping rapids and one more 30-metre drop lower down. The water flows on into rivers that join the Orinoco.
The waterfall is named after Jimmie Angel, an American pilot. He was the first person to fly over it, on 16 November 1933. The Pemon people, who live in the region, call it Kerepakupai Vená. In 2009 Venezuela’s president Hugo Chávez spoke in favour of using the Pemon name.
Angel Falls has a close rival. Tugela Falls in the Drakensberg mountains of South Africa drops 948 metres in five separate leaps. Both were measured from far away, so nobody is completely sure which one is really taller. Angel Falls is usually named the tallest uninterrupted waterfall in the world.
Victoria Falls: “The Smoke That Thunders”
Victoria Falls is on the Zambezi River, right on the border between Zambia and Zimbabwe. It is nowhere near the tallest waterfall. So why do people call it the largest? Because it is both wide and tall. The whole river drops as much as 108 metres in one go, along a line 1,708 metres long. That makes the biggest single sheet of falling water in the world.
The water falls into a narrow crack in the rock called the First Gorge. The only way out is a gap about 110 metres wide. So the whole huge river squeezes through that one slot.
The local Lozi name is Mosi-oa-Tunya, which means “the smoke that thunders”. The spray rises like smoke, and the roar sounds like thunder. The Scottish explorer David Livingstone was the first European known to see the falls, on 16 November 1855. He named them after Queen Victoria. Both names are used today.
Iguazu Falls: Hundreds of Waterfalls in One
Iguazu Falls sits on the Iguazu River, on the border between Argentina and Brazil. Its name comes from Guarani or Tupi words meaning “big water”. Together the falls make up the largest waterfall system in the world.
The edge of the falls is 2.7 kilometres long. Islands split the river into many separate falls, between 60 and 82 metres high. When the river is low there are about 150 of them. When it is high there can be about 300. Almost 80 percent of the falls are on the Argentine side.
About half of all the water pours into one long, narrow chasm called the Devil’s Throat. In Spanish it is Garganta del Diablo. It is 80 to 90 metres wide and 70 to 80 metres deep. The border between the two countries runs right through it. Argentina protected its side as a UNESCO World Heritage Site in 1984, and Brazil followed in 1986.
Boyoma and Inga: The Congo River’s Water Champions
Tall waterfalls are not always the most powerful. The record for the most water belongs to falls you might never have heard of, on the Congo River in the Democratic Republic of the Congo.
The Boyoma Falls are a chain of seven small falls on the Lualaba River, the upper part of the Congo. They stretch over more than 100 kilometres between the towns of Ubundu and Kisangani. None of the steps is more than 5 metres high, and the total drop is 61 metres. But so much water rushes through that they are the largest waterfall in the world by yearly flow, beating both Niagara and Iguazu. Local Wagenya fishermen set big baskets in the rapids, tied to wooden poles wedged into holes in the rock, to catch large fish.
Further down the Congo River are the Inga Falls, near the city of Matadi. Here the river drops 96 metres over 15 kilometres. Usually about 42,000 cubic metres of water pass every second. At its highest, the flow has reached 71,000. Niagara averages about 2,400. Many experts say Inga is really a set of rapids, not a true waterfall, which is why it is not always on record lists.
Plunge, Horsetail, Cascade and Tiered: Waterfall Types in Yosemite and Beyond
Scientists sort waterfalls by the way the water falls. Here are some of the main types.
- Plunge: the water drops straight down and loses touch with the rock. The great free fall of Angel Falls is a plunge.
- Horsetail: the water keeps touching the rock as it slides down, like a horse’s swishing tail. Despite its name, Horsetail Fall in Yosemite National Park, California, drops mostly through the air. It flows only in winter and early spring. On some February evenings, the setting sun makes it glow orange and red, so people call it the “Firefall”.
- Cascade: the water bounces down a staircase of rock steps.
- Tiered: several falls follow one after another. Yosemite Falls has three tiers: the Upper Fall drops 440 metres, the Middle Cascades 206 metres, and the Lower Fall 98 metres.
- Block or sheet: water falls from a wide river in a broad curtain, like Victoria Falls.
- Segmented: the water splits into separate streams as it falls, often around rocks or islands at the edge.
Yosemite has so many waterfalls because of glaciers. Long ago, a huge glacier deepened the main valley more than the side valleys. Those side valleys were left “hanging” high on the cliffs. Their streams now spill over the edge as waterfalls.
Frozen Niagara and the Swifts That Nest Behind the Spray
In very cold places, waterfalls can freeze. Usually the outside turns to ice while water keeps running underneath. Climbers with ice axes and spiked boots called crampons even climb frozen waterfalls for sport.
Niagara Falls ices up most winters but almost never stops. On 29 March 1848, though, a jam of ice blocked the river upstream. For as long as 40 hours, hardly any water went over the falls. Water-powered mills and factories had to shut down. In 1912 the American Falls froze completely, while the bigger Horseshoe Falls kept flowing. Niagara also partly froze in other years, including 1911, 2014, 2017 and 2019.
Waterfalls are home to some tough animals. The great dusky swift of South America nests in big colonies on cliffs beside or behind waterfalls. At Iguazu it is known for flying straight through the falling water. In North America, the American black swift builds its mossy nest behind or next to waterfalls too. One place it nests is Johnston Canyon in Banff National Park, Canada. The American dipper, a small grey songbird, sometimes builds its round nest behind a waterfall as well.
In Hawaii, a little fish does something even more surprising. Young Nopili rock-climbing gobies hatch in mountain streams and are washed out to sea. When they come back, they climb the wet rock under and beside very high waterfalls. They hold on with suckers made from their mouth and their belly fins.
For more on the record-holders, take a closer look at Angel Falls, learn about the rock behind Niagara Falls’ geography, or compare flow rates in our list of the most powerful waterfalls in the world.