Waterfall

Last updated

Angel Falls in Venezuela is the world's tallest waterfall at 979 m (3,212 ft). Salto del Angel-Canaima-Venezuela08.JPG
Angel Falls in Venezuela is the world's tallest waterfall at 979 m (3,212 ft).

A waterfall is an area where water flows over a vertical drop or a series of steep drops in the course of a stream or river. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf.

Contents

Formation

Formation of a waterfall WaterfallCreationDiagram.svg
Formation of a waterfall

Waterfalls are commonly formed in the upper course of a river where lakes fall into in steep mountains. [1] Because of their landscape position, many waterfalls occur over bedrock fed by little contributing area, so they may be ephemeral and flow only during rainstorms or significant snowmelt. The further downstream, the more perennial a waterfall can be. Waterfalls can have a wide range of widths and depths.

Aerial view of Victoria Falls on the Zambezi River in southern Africa. The cloud formed by the mist is called cataractagenitus. Victoria Falls (2541711854).jpg
Aerial view of Victoria Falls on the Zambezi River in southern Africa. The cloud formed by the mist is called cataractagenitus.

When the river courses over resistant bedrock, erosion happens slowly and is dominated by impacts of water-borne sediment on the rock, while downstream the erosion occurs more rapidly. [1] [3] As the watercourse increases its velocity at the edge of the waterfall, it may pluck material from the riverbed, if the bed is fractured or otherwise more erodible. Hydraulic jets and hydraulic jumps at the toe of a falls can generate large forces to erode the bed, [4] especially when forces are amplified by water-borne sediment. Horseshoe-shaped falls focus the erosion to a central point, also enhancing riverbed change below a waterfalls. [5] A process known as "potholing" involves local erosion of a potentially deep hole in bedrock due to turbulent whirlpools spinning stones around on the bed, drilling it out. Sand and stones carried by the watercourse therefore increase erosion capacity. [1] 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. [6] The rate of retreat for a waterfall can be as high as one-and-a-half metres per year. [1]

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 in the gorge downstream.

Streams can 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. However, a study of waterfalls systematics reported that waterfalls can be wider or narrower above or below a falls, so almost anything is possible given the right geological and hydrological setting. [7] 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. [1] 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. [1]

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); and Sutherland Falls (Class 5). [8]

Researchers

Alexander von Humboldt (1820s) "Father of Modern Geography" Humboldt was mostly marking waterfalls on maps for river navigation purposes.

Oscar von Engeln (1930s) Published "Geomorphology: systematic and regional", this book had a whole chapter devoted to waterfalls, and is one of the earliest examples of published works on waterfalls.

R. W. Young (1980s) Wrote "Waterfalls: form and process" this work made waterfalls a much more serious topic for research for modern Geoscientists. [9]

Types

An example of an ephemeral waterfall. This one, when flowing, feeds into the Chagrin River (Ohio). An ephemeral waterfall.jpg
An example of an ephemeral waterfall. This one, when flowing, feeds into the Chagrin River (Ohio).

Some waterfalls are also distinct in that they do not flow continuously. Ephemeral waterfalls only flow after a rain or a significant snowmelt. [11] [12] [13]

Examples

Significant waterfalls, [15] listed alphabetically:

See also

Related Research Articles

Iguazu Falls

Iguazú Falls or Iguaçu Falls are waterfalls of the Iguazu River on the border of the Argentine province of Misiones and the Brazilian state of Paraná. Together, they make up the largest waterfall in the world. The falls divide the river into the upper and lower Iguazu. The Iguazu River rises near the heart of the city of Curitiba. For most of its course, the river flows through Brazil; however, most of the falls are on the Argentine side. Below its confluence with the San Antonio River, the Iguazu River forms the border between Argentina and Brazil.

Yosemite Valley

Yosemite Valley is a glacial valley in Yosemite National Park in the western Sierra Nevada mountains of Central California. The valley is about 7.5 miles (12 km) long and approximately 3000–3500 feet deep, surrounded by high granite summits such as Half Dome and El Capitan, and densely forested with pines. The valley is drained by the Merced River, and a multitude of streams and waterfalls flow into it, including Tenaya, Illilouette, Yosemite and Bridalveil Creeks. Yosemite Falls is the highest waterfall in North America and is a big attraction especially in the spring, when the water flow is at its peak. The valley is renowned for its natural environment and is regarded as the centerpiece of Yosemite National Park, attracting visitors from around the world.

Niagara Escarpment

The Niagara Escarpment is a long escarpment, or cuesta, in the United States and Canada that runs predominantly east–west from New York, through Ontario, Michigan, Wisconsin, and Illinois. The escarpment is most famous as the cliff over which the Niagara River plunges at Niagara Falls, for which it is named.

Angel Falls waterfall in Venezuela and the tallest uninterrupted waterfall in the world

Angel Falls is a waterfall in Venezuela. It is the world's highest uninterrupted waterfall, with a height of 979 metres (3,212 ft) and a plunge of 807 m (2,648 ft). The waterfall drops over the edge of the Auyán-tepui mountain in the Canaima National Park, a UNESCO World Heritage site in the Gran Sabana region of Bolívar State. The height figure, 979 m (3,212 ft), mostly consists of the main plunge but also includes about 400 metres (1,300 ft) of sloped cascade and rapids below the drop and a 30-metre (98 ft) high plunge downstream of the talus rapids.

Fluvial processes Processes associated with rivers and streams

In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.

Mardalsfossen

Mardalsfossen is a waterfall in Molde Municipality in Møre og Romsdal county, Norway. It is sometimes referred to as one of the tallest waterfalls in Europe. The falls are on the Mardøla river which flows out of a hanging valley into the lake Eikesdalsvatnet, about 2 kilometres (1.2 mi) northwest of the village of Eikesdalen. The waterfall was depicted in the coat of arms of the old Nesset Municipality.

Giants kettle

A giant's kettle, also known as either a giant's cauldron, moulin pothole, or glacial pothole, is a typically large and cylindrical pothole drilled in solid rock underlying a glacier either by water descending down a deep moulin or by gravel rotating in the bed of subglacial meltwater stream.

Knickpoint

In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous erosion due to glaciation or variance in lithology. In the cycle of erosion model, knickpoints advance one cycle upstream, or inland, replacing an older cycle.

Plunge pool Depression at the base of a waterfall created by the erosional force of falling water and rocks where it lands

A plunge pool is a deep depression in a stream bed at the base of a waterfall or shut-in. It is created by the erosional forces of cascading water on the rocks at formation's base where the water impacts. The term may refer to the water occupying the depression, or the depression itself.

Augrabies Falls

The Augrabies Falls is a waterfall on the Orange River, the largest river in South Africa. Since 1966 the waterfall, set in a desolate and rugged milieu, is enclosed by the Augrabies Falls National Park. The falls are around 183 feet (56 m) in height. Some sources cite an approximate height of 480 feet; this is actually the height from the base of the canyon to the top of the walls, not that of the falls themselves.

Wapama Falls

Wapama Falls is the larger of two waterfalls located on the northern wall of Hetch Hetchy Valley in Yosemite National Park. It flows almost year-round and during peak flow has been known to inundate the trail bridge crossing its base, making the falls impossible to pass. The falls consist of two primary drops angled roughly 60 degrees to each other, and a broad cascade at its base. Wapama Falls is fed by Lake Vernon, a few miles to the north, and is below Hetch Hetchy Dome.

Horsetail Fall (Yosemite)

Horsetail Fall, located in Yosemite National Park in California, is a seasonal waterfall that flows in the winter and early spring. The fall occurs on the east side of El Capitan. If Horsetail Fall is flowing in February and the weather conditions are just right, the setting sun illuminates the waterfall, making it glow orange and red. This natural phenomenon is often referred to as the "Firefall", a name that pays homage to Yosemite Firefall, the manmade event that once took place in Yosemite.

Stream Body of surface water flowing down a channel

A stream is a body of water with surface water flowing within the bed and banks of a channel. The flow of a stream is controlled by three inputs - surface water, subsurface water and groundwater. The surface and subsurface water are highly variable between periods of rainfall. Groundwater, on the other hand, has a relatively constant input and is controlled more by long-term patterns of precipitation. The stream encompasses surface, subsurface and groundwater fluxes that respond to geological, geomorphological, hydrological and biotic controls.

River Natural flowing watercourse

A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.

Waterfall Country is an English name often given to the Vale of Neath in South Wales. The tourist area around the head of valley has an unusually large number of publicly accessible waterfalls. The area is not officially defined but generally includes the group of falls on the Nedd Fechan, Pyrddin, Hepste and Mellte rivers, all of which lie between the villages of Pontneddfechan and Ystradfellte in the Brecon Beacons National Park.

Salt Creek Falls

Salt Creek Falls is a cascade and plunge waterfall on Salt Creek, a tributary of the Middle Fork Willamette River, that plunges into a gaping canyon near Willamette Pass in the Willamette National Forest, near Oakridge, Oregon. The waterfall is notable for its main drop of 286 feet (87 m) which makes it the third highest plunge waterfall in Oregon after Multnomah Falls and Watson Falls the second highest, which was re-measured in 2009 and found to be 293 feet rather than an earlier measurement of 272 feet passing Salt Creek Falls. The pool at the bottom of the waterfall is 20 metres (66 ft) deep.

Pothole (landform) Natural bowl-shaped hollow carved into a streambed

In Earth science, a pothole is a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, found carved into the rocky bed of a watercourse. Other names used for riverine potholes are pot, (stream) kettle, giant's kettle, evorsion, hollow, rock mill, churn hole, eddy mill, and kolk. Although somewhat related to a pothole in origin, a plunge pool is the deep depression in a stream bed at the base of a waterfall. it is created by the erosional forces of turbulence generated by water falling on rocks at a waterfall's base where the water impacts. Potholes are also sometimes referred to as swirlholes. This word was created to avoid confusion with an English term for a vertical or steeply inclined karstic shaft in limestone. However, given widespread usage of this term for a type of fluvial sculpted bedrock landform, pothole is preferred in usage to swirlhole.

References

  1. 1 2 3 4 5 6 Carreck, Rosalind, ed. (1982). The Family Encyclopedia of Natural History. The Hamlyn Publishing Group. pp. 246–248. ISBN   978-0711202252.
  2. Sutherland, Scott (23 March 2017). "Cloud Atlas leaps into 21st century with 12 new cloud types". The Weather Network. Pelmorex Media. Retrieved 24 March 2017.
  3. 1 2 3 4 5 "Adventure". 16 June 2008. Retrieved 10 November 2016.
  4. Pasternack, Gregory B.; Ellis, Christopher R.; Marr, Jeffrey D. (1 July 2007). "Jet and hydraulic jump near-bed stresses below a horseshoe waterfall". Water Resources Research. 43 (7): W07449. Bibcode:2007WRR....43.7449P. doi:10.1029/2006wr005774. ISSN   1944-7973.
  5. "Dr. Gregory B. Pasternack - Watershed Hydrology, Geomorphology, and Ecohydraulics :: Horseshoe Falls". pasternack.ucdavis.edu. Retrieved 11 June 2017.
  6. "Observe river erosion creating waterfalls and chasms" . Retrieved 10 November 2016.
  7. Wyrick, Joshua R.; Pasternack, Gregory B. (1 September 2008). "Modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps". Journal of Geophysical Research: Earth Surface. 113 (F3): F03003. Bibcode:2008JGRF..113.3003W. doi:10.1029/2007jf000873. ISSN   2156-2202.
  8. Richard H. Beisel Jr., International Waterfall Classification System, Outskirts Press, 2006 ISBN   1-59800-340-2
  9. Hudson, B. J. (2013) Waterfalls, science and aesthetics
  10. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 "Worldwaterfalls.com". 11 September 2015. Retrieved 10 November 2016.
  11. https://www.terragalleria.com Ephemeral waterfall seen from inside cave. Mammoth Cave National Park.
  12. https://www.kidsdiscover.com About Horsetail Falls, One of Yosemite's Ephemeral Waterfalls.
  13. https://www.wncwaterfalls Bird Rock Falls.
  14. "Showing all Waterfalls in India". World Waterfalls Database. Archived from the original on 1 September 2009. Retrieved 20 June 2010.
  15. "World Waterfall Database - The webs most authoritative source about Waterfalls". Archived from the original on 12 July 2011. Retrieved 10 November 2016.
  16. "Falls of Lora Information" The Falls of Lora. Retrieved 18 September 2011.