Waterfalls are commonly formed in the upper course of the river. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens slowly, while downstream the erosion occurs more rapidly. As the watercourse increases its velocity at the edge of the waterfall, it plucks material from the riverbed. Whirlpools created in the turbulence as well as sand and stones carried by the watercourse increase the erosion capacity. This causes the waterfall to carve deeper into the bed and to recede upstream. Often over time, the waterfall will recede back to form a canyon or gorge downstream as it recedes upstream, and it will carve deeper into the ridge above it. The rate of retreat for a waterfall can be as high as one and half meters per year.
Often, the rock stratum just below the more resistant shelf will be of a softer type, meaning that undercutting due to splashback will occur here to form a shallow cave-like formation known as a rock shelter under and behind the waterfall. Eventually, the outcropping, more resistant cap rock will collapse under pressure to add blocks of rock to the base of the waterfall. These blocks of rock are then broken down into smaller boulders by attrition as they collide with each other, and they also erode the base of the waterfall by abrasion, creating a deep plunge pool or gorge.
Streams become wider and shallower just above waterfalls due to flowing over the rock shelf, and there is usually a deep area just below the waterfall because of the kinetic energy of the water hitting the bottom. Waterfalls normally form in a rocky area due to erosion. After a long period of being fully formed, the water falling off the ledge will retreat, causing a horizontal pit parallel to the waterfall wall. Eventually, as the pit grows deeper, the waterfall collapses to be replaced by a steeply sloping stretch of river bed. In addition to gradual processes such as erosion, earth movement caused by earthquakes or landslides or volcanoes can cause a differential in land heights which interfere with the natural course of a water flow, and result in waterfalls.
A river sometimes flows over a large step in the rocks that may have been formed by a fault line. Waterfalls can occur along the edge of a glacial trough, where a stream or river flowing into a glacier continues to flow into a valley after the glacier has receded or melted. The large waterfalls in Yosemite Valley are examples of this phenomenon, which is referred to as a hanging valley. Another reason hanging valleys may form is where two rivers join and one is flowing faster than the other. Waterfalls can be grouped into ten broad classes based on the average volume of water present on the fall (which depends on both the waterfall's average flow and its height) using a logarithmic scale. Class 10 waterfalls include Niagara Falls, Paulo Afonso Falls and Khone Falls.
Classes of other well-known waterfalls include Victoria Falls and Kaieteur Falls (Class 9); Rhine Falls and Gullfoss (Class 8); Angel Falls and Dettifoss (Class 7); Yosemite Falls, Lower Yellowstone Falls and Umphang Thee Lor Sue Waterfall (Class 6); Sutherland Falls (Class 5).
- Ledge waterfall: Water descends vertically over a vertical cliff, maintaining partial contact with the bedrock.
- Plunge: Fast moving water descends vertically, losing complete contact with the bedrock surface. The contact is typically lost due to horizontal thrust of the water before it falls. It always starts from a narrow stream.
- Punchbowl: Water descends in a constricted form and then spreads out in a wider pool.
- Horsetail: Descending water maintains good contact with bedrock most of the time.
- Cascade: Water descends a series of rock steps.
- Tiered/Multi-step/Staircase: A series of waterfalls one after another of roughly the same size each with its own sunken plunge pool.
- Cataract: A large, powerful waterfall.
- Segmented: Distinctly separate flows of water form as it descends.
- Catadupa: A cataract or waterfall, originally those of the Nile. The term catadupae refers to people inhabiting near such cataracts; there are suppositions that these people are deaf due to the constant din.
- Tide fall: A waterfall that directly empties into the sea or ocean.
- Frozen: Any waterfall which has some element of ice or snow.
Examples of famous waterfalls
Significant waterfalls, listed alphabetically:
- Angel Falls in Venezuela is the world's tallest above-water waterfall at Script error: No such module "convert"..
- Ban Gioc–Detian Falls, a transnational waterfall on the border between China and Vietnam.
- Bridalveil Fall in Yosemite Valley is Script error: No such module "convert". high with a sheer drop.
- Cumberland Falls in Kentucky is one of several falls in the world at which a moonbow is visible.
- Dettifoss in northeast Iceland is the largest waterfall in Europe in terms of volume discharge, having an average water flow of 200 m³/s.The falls are Script error: No such module "convert". wide and have a drop of Script error: No such module "convert". down to the Jökulsárgljúfur canyon.
- Eas a' Chual Aluinn in Scotland, at Script error: No such module "convert"., the tallest waterfall in the United Kingdom.
- Falls of Lora, also in Scotland, is an unusual rapids in the sea that is created when the waters in Loch Etive pour out through the narrow mouth of the loch over a rocky shelf.
- Gocta, the sixteenth tallest in the world at Script error: No such module "convert"., is located in the province of Chachapoyas, Peru.
- Huangguoshu Waterfall in Anshun, Guizhou, China, is the largest waterfall in East Asia.
- Iguazu Falls is an extensive series of waterfalls along a 2.7-km (1.7-mile) stretch of escarpment on the Argentina-Brazil border.
- James Bruce Falls, the tallest waterfall in North America at Script error: No such module "convert"., is located in the Princess Louisa Marine Provincial Park, British Columbia, Canada.
- Jiao Lung Waterfall in Alishan, Chiayi, Taiwan, is the tallest waterfall in East Asia at Script error: No such module "convert"..
- Jog Falls in Karnataka, India, is the second-highest plunge waterfall in India.
- Kaieteur Falls (Potaro River in central Guyana), located in the Kaieteur National Park, is Script error: No such module "convert"..
- Niagara Falls are the widest, most powerful falls in North America.
- Nohkalikai Falls is India's tallest plunge waterfall, located in Meghalaya state, India.
- Pissing Mare Falls, at Script error: No such module "convert"., is among the tallest waterfalls in eastern North America.
- Ramnefjellsfossen in Stryn, Nesdalen, Norway, is the world's third tallest at Script error: No such module "convert"..
- Reichenbach Falls in Switzerland, a series of falls totaling Script error: No such module "convert". in height, were the site of the disappearance and purported death of fictional detective Sherlock Holmes in the story "The Final Problem".
- Rhine Falls near Schaffhausen, Switzerland, are among the largest in Europe, at Script error: No such module "convert". wide.
- Ribbon Fall, a seasonal waterfall in Yosemite National Park, is the highest single-drop fall in North America, at Script error: No such module "convert"..
- Shir-Abad Waterfall is located near Khan Bebin in Golestan Province, Iran.
- Shoshone Falls in Idaho has been termed the "Niagara of the West".
- St.Clair's Falls, Sri Lanka's widest waterfall, is Script error: No such module "convert". tall.
- Takakkaw Falls, Script error: No such module "convert". high, are in Yoho National Park in Canada.
- Tequendama Falls is a Script error: No such module "convert". waterfall on the Bogotá River, about Script error: No such module "convert". southwest of Bogotá in Colombia.
- Tugela Falls is the world's second tallest at Script error: No such module "convert". in KwaZulu-Natal province, Republic of South Africa.
- Venta Rapid in Latvia, said to be Europe's widest waterfall, is more than Script error: No such module "convert". wide but only about Script error: No such module "convert". high.
- Victoria Falls, on the Zambezi river along the border between Zimbabwe and Zambia, is among the largest waterfalls in the world. During periods of high flow, it creates an unbroken sheet of water more than a mile wide.
- Virginia Falls (Northwest Territories) on South Nahanni River, Northwest Territories, Canada. World's 14th largest waterfall located in Nahanni National Park Reserve a UNESCO World Heritage Site.
- Waihilau Falls, at Script error: No such module "convert"., is located in the Waimanu Valley, Hawaii, United States.
- Yosemite Falls, Script error: No such module "convert"., located in Yosemite National Park, United States.
- Yumbilla Falls is the world's fifth tallest waterfall and located in Peru.
- Thailand 484 song khon.jpg
Song Khon Waterfall in Loei Province, Thailand is an example of a cascade waterfall.
- 1st fall of the Elephant falls, Shillong.jpg
First fall of Elephant Falls in Shillong, India, is an example of a horsetail-punchbowl waterfall.
- Sempervirens Falls.JPG
Sempervirens Falls in California, USA, is an example of a plunge-punchbowl waterfall.
- Plitvice Lakes, Barrier between Gavanovac and Kaluderovac.JPG
Several of the scores of waterfalls of various types at Plitvice Lakes, Croatia
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- List of waterfalls
- List of waterfalls by height
- List of waterfalls by flow rate
- List of waterfalls by type
- Stream pool
- Water feature
- Artificial waterfall
- Carreck, Rosalind, ed. (1982). The Family Encyclopedia of Natural History. The Hamlyn Publishing Group. pp. 246–248. ISBN 0711202257.
- Richard H. Beisel Jr., International Waterfall Classification System, Outskirts Press, 2006 ISBN 1-59800-340-2
- 12px This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). "Catadupa". Cyclopædia, or an Universal Dictionary of Arts and Sciences (first ed.). James and John Knapton, et al. p. 169.
- World Waterfall Database
- "Falls of Lora Information" The Falls of Lora. Retrieved 18 Sept 2011.
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