Why do waterfalls retreat?

January 1, 2021

Did you know that waterfalls themselves, and not just the water in them, are constantly moving? The water rushes forward and falls, but the waterfall itself is slowly sliding back. This paradox can easily be explained by the laws of nature.

ISSUE: #02 JANUARY 2021

Topic Last Updated on 08-07-2024

Nature’s Erosion in Action

It seems simple enough: a river encounters a cliff, creating a waterfall. But where did the cliﬀ come from? Of course, it could occur as the result of an earthquake in the streambed of the river, but usually, it’s the river itself that forms the waterfall.

Waterfalls form in areas where hard rock meets soft rock. Initially, the river flows along a straight channel, but over time the soft rock begins to erode. A plunge pool forms, with a ledge hanging over it — that’s how a waterfall is created. However, hard rock can’t resist the water flow forever; the rocky ledge eventually wears away, causing the waterfall to “recede” towards the river source. For example, Niagara Falls moves backward by about about 12 in a year!

Waterfall Formation

A cliff can end up receding until it reaches a human settlement or a bridge. This process cannot be stopped completely, but it can be slowed down. To do so, the government regulates the volume of the water stream and diverts part of it towards hydroelectric power stations. Taking all the necessary precautions can decrease the velocity of Niagara Falls by 10 times while increasing the production of clean energy.

Waterfalls are not only spectacular but also very noisy. This happens because rocky grottoes, high humidity, and temperature inversion collect and bend sound waves.

For example, in the rainy season, the noise of Victoria Falls spreads across 25 mi, and people right next to the falls can hardly hear one another.

In of spite their seeming simplicity, waterfalls can have varying and peculiar shapes: “horsetail,” “bridal veil,” “crevice,” “curtain,” “fan,” “leaf,” etc. However, there is no strict classification. As usual, we will take a look at the most notable examples.

Angel Falls (Kerepakupai Merú)

Height: 3,212 ft

Location: Venezuela

Over half a mile long, this is the tallest waterfall on the planet. In 1933, American pilot James Angel was searching for gold and diamond reserves in the mountains of Venezuela. He did not find any precious stones, but, from high up in the sky, he spotted a hill with a tremendous waterfall. The plane broke down when Angel attempted a landing, so he and his passengers had to descend the mountain on foot and walk another 11 days to reach civilization. The adventure made it to the world news, and the waterfall (already known to geographers, by the way) was named in Angel’s honor. In 2009, President of Venezuela Hugo Chávez suggested the waterfall be renamed to Kerepakupai Merú (“Waterfall of the deepest place” in the indigenous Pemon language). That way, the country’s most famous landmark bore a local name.

Victoria Falls

Height: 354 ft

Location: Zambia, Zimbabwe

This waterfall is not a record-breaker in any specific category, but it could be named the “golden mean.” Victoria Falls has both an impressive height and width (5,604 ft). Each second, more than a thousand cubic meters of water flow over the falls, and even more in the rainy season. The natural wonder was discovered by a prominent explorer of Africa, David Livingstone — or rather, he was the one to introduce it to Europe. Local people clearly knew about the waterfall long before. In fact, they guided Livingstone’s expedition to the destination. The British explorer named his finding in honor of Queen Victoria. The indigenous name, Mosi-oa-Tunya, means “the smoke that thunders” — spray from the waterfall rises hundreds of meters up into the air and forms a thick fog.

Niagara Falls

Height: 174 ft

Location: US, Canada

Niagara Falls is not one, but three waterfalls. This hasn’t always been the case — around 600 years ago, Niagara Falls was whole. The waterfall moved over time and reached a group of islands that separated it into three. Each of the waterfalls in the resulting complex received its own name: Horseshoe Falls (also called Canadian Falls), American Falls, and Bridal Veil Falls. Despite the region’s cold winters, Niagara Falls doesn’t usually freeze, with some exceptions (for instance, 2018 and 2019). Niagara’s hydroelectric stations supply over a quarter of all electricity used in the Canadian province of Ontario and New York state. The hydroelectric station uses more water at night than in the daytime so that tourists can fully enjoy the grand spectacle.

Khone Falls

Height: 69 ft

Location: Laos

By the standards of other waterfalls, the Khone seems quite small, but make no mistake: 69 ft is around the height of a seven-story house! The Khone Falls leads in a diﬀerent category: the total width of its cascades (35,377 ft!) makes it the widest on the planet. It is practically impossible to raft along the Mekong river, where the Khone is located, because the area is full of rapids and tiny islands. However, during flood seasons, the river “swallows” all the irregularities, causing the waterfall to disappear into the deep water. Moreover, around the Khon, you can find the largest freshwater fish on Earth — the gigantic catfish Pangasianodon gigas. Its specimens can reach a mass of up to 440–660 lb. Such a giant is an attractive prey for fishermen; thus, the species is under threat of extinction.

Guaíra Falls

Height: 375 ft

Location: Brazil, Paraguay

Despite its unremarkable size, Guaíra Falls had incredible power. According to various estimates, its flow rate ranged from 460,000 to 1,765,733 ft³ per second, which made it the highest volume of falling water in the world. Why are we talking about it in the past tense? The Guaíra no longer exists — in 1982, the building of a dam and artificial lake on the Paraná River submerged the waterfall. As soon as the project went public, thousands of tourists flocked to the area to see the falls for the last time. This led to tragedy: a bridge serving as an observation platform collapsed under the weight of the tourists, and forty people drowned.