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.
Waterfalls are commonly formed in the upper course of a river in steep mountains.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.
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.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, 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. 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. 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-a-half metres 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 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.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); and Sutherland Falls (Class 5).
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.
Some waterfalls are also distinct in that they do not flow continuously. Ephemeral waterfalls only flow after a rain or a significant snowmelt.
Significant waterfalls,listed alphabetically:
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Yosemite Falls is the highest waterfall in Yosemite National Park, dropping a total of 2,425 feet (739 m) from the top of the upper fall to the base of the lower fall. Located in the Sierra Nevada of California, it is a major attraction in the park, especially in late spring when the water flow is at its peak.
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 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.
The Wallaman Falls, a cascade and horsetail waterfall on the Stony Creek, is located in the UNESCO World Heritage–listed Wet Tropics in the locality of Wallaman, Shire of Hinchinbrook in the northern region of Queensland, Australia. The waterfall is notable for its main drop of 268 metres (879 ft), which makes it the country's tallest single-drop waterfall. The pool at the bottom of the waterfall is 20 metres (66 ft) deep. An estimated 100,000 people visit the waterfall annually.
Jog Falls located near Jog Village. Falling point of water is located in Siddapur, Uttara Kannada and the view point in Sagara Karnataka. Jog Falls is also known as Gerusoppe falls, Joga jalapatha and Jogada gundi in the regional Kannada language.
Kaieteur Falls is the world's largest single drop waterfall by the volume of water flowing over it. Located on the Potaro River in the Kaieteur National Park, it sits in a section of the Amazon rainforest included in the Potaro-Siparuni region of Guyana. It is 226 metres (741 ft) high when measured from its plunge over a sandstone and conglomerate cliff to the first break. It then flows over a series of steep cascades that, when included in the measurements, bring the total height to 251 metres (822 ft). While many falls have greater height, few have the combination of height and water volume, and Kaieteur is among the most powerful waterfalls in the world with an average flow rate of 663 cubic metres per second.
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.
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.
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.
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.
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.
A stream pool, in hydrology, is a stretch of a river or stream in which the water depth is above average and the water velocity is below average.
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.
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.
Overdeepening is a characteristic of basins and valleys eroded by glaciers. An overdeepened valley profile is often eroded to depths which are hundreds of metres below the deepest continuous line along a valley or watercourse. This phenomenon is observed under modern day glaciers, in salt-water fjords and fresh-water lakes remaining after glaciers melt, as well as in tunnel valleys which are partially or totally filled with sediment. When the channel produced by a glacier is filled with debris, the subsurface geomorphic structure is found to be erosionally cut into bedrock and subsequently filled by sediments. These overdeepened cuts into bedrock structures can reach a depth of several hundred metres below the valley floor.
The Earth scientists, who study rivers and streams, define a pothole as 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.