Waterfall
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A waterfall is usually a geological formation resulting from water, often in the form of a stream, flowing over an erosion-resistant rock formation that forms a nickpoint, or sudden break in elevation.
Some waterfalls form in mountain environments in which the erosive water force is high and stream courses may be subject to sudden and catastrophic change. In such cases, the waterfall may not be the end product of many years of water action over a region, but rather the result of relatively sudden geological processes such as landslides, faults or volcanic action. In cold places, snow will build up in winter and melt and turn into a waterfall in summer.
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[edit] Formation
Typically, a river flows only once a month over a large step in the rocks that may have been formed by a fault line. As it increases its velocity at the edge of the waterfall, it plucks material from the riverbed. 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.
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 or plunge pool 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 pool 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.
Waterfalls can occur along the edge of glacial trough, whereby 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. The rivers are flowing from hanging valleys.
[edit] Classifying Waterfalls
Waterfalls are grouped into ten broad classes based on the average volume of water present on the fall using a logarithmic scale. Class 10 waterfalls include Niagara Falls, Paulo Alfonso Falls and Khone Falls.
Classes of other well-known waterfalls include Victoria Falls and Kaieteur Falls (Class 9); Rhine Falls, Gullfoss and Sutherland Falls (Class 8); Angel Falls and Dettifoss (Class 7); Yosemite Falls and Lower Yellowstone Falls and Umphang Thee Lor Sue Water Fall Thailand (Class 6).[1]
[edit] Types of waterfalls
- Block: Water descends from a relatively wide stream or river.
- Cascade: Water descends a series of rock steps.
- Cataract: A large, powerful waterfall.
- Fan: Water spreads horizontally as it descends while remaining in contact with bedrock.
- Horsetail: Descending water maintains some contact with bedrock.
- Plunge: Water descends vertically, losing contact with the bedrock surface.
- Punchbowl: Water descends in a constricted form and then spreads out in a wider pool.
- Segmented: Distinctly separate flows of water form as it descends.
- Tiered: Water drops in a series of distinct steps or falls.
- Multi-step: A series of waterfalls one after another of roughly the same size each with its own sunken plunge pool.
[edit] Examples of large waterfalls
Significant waterfalls are listed alphabetically:
- Angel Falls is the world's highest at 979 metres (3212 feet) in Venezuela.
- Bambarakanda Falls is Sri Lanka's tallest waterfall at 263 m.
- Bridalveil Fall in Yosemite Valley is 189 m (620 ft) high with a sheer drop when flowing.
- Cascata delle Marmore in Italy is the tallest man-made waterfall in the world.
- Cautley Spout, at 175 m (580 ft), is the highest waterfall in England.
- Colonial Creek Falls, the tallest waterfall in North America at 2,584 ft (788 m), is located in the North Cascades National Park, Washington, United States.
- Eas a' Chual Aluinn, at 200 m (658 ft), is the highest waterfall in both Scotland and the United Kingdom.
- Gocta is the fifth-highest in the world at 771 m (2532 ft) and located in the province Chachapoyas, Peru.
- Hannoki Falls is the tallest waterfall in Asia at 1,640 ft (500 m) and located in Tateyama, Japan.
- High Force on the River Tees is one of the tallest waterfalls in England.
- Huangguoshu Waterfall in Anshun, Guizhou, China, is the largest waterfall in Asia.
- Iguazu Falls are tall and extremely wide falls located in South America on the Argentina/Brazil border.
- Jog Falls is India's eighth-highest (listed as 314 ranking on the World Waterfall Database), located in Karnataka state, India.
- Jurong Falls in Singapore is the tallest artificial waterfall in the world.
- Kaieteur Falls (Potaro River in central Guyana), located in the Kaieteur National Park, is 226 m (741 ft).
- Krimmler Wasserfälle, at 380 m, is Austria's second tallest waterfall and located in Krimml, Salzburg, Austria.
- Multnomah Falls is 611 feet (186 m) high and 30 ft wide.
- Niagara Falls are the most powerful falls in North America.
- Pissing Mare Falls, at 350 m (1148 ft), are the highest in eastern North America.
- Ramnefjellsfossen is the world's third-highest at 808 m (2685 ft), at Stryn, Nesdalen, Norway.
- Rhine Falls are Europe's widest and located in Switzerland.
- ShirAbad Waterfall is located in Iran, Golestan,Khanbebin, Shirabad.
- St.Clair's Falls is Sri Lanka's widest waterfall 265 ft high.
- Tequendama Falls is a 132m high waterfall on the Bogotá River, about 30 km southwest of Bogotá in Colombia.
- Tugela Falls is the world's second-highest at 947 m (3110 ft) in KwaZulu-Natal province, Republic of South Africa.
- Victoria Falls is the largest waterfall in the world and is more than a mile long. It is located on the Zambezi river on the border of Zimbabwe and Zambia.
- Waihilau Falls, the tallest waterfalls in the United States at 2,600 ft (792 m), are located in the Waimanu Valley, Hawaii, United States.
- Yosemite Falls, the second tallest in North America at 2,425 ft, is located in Yosemite National Park, United States.
- Yumbilla Falls is the world's fifth-tallest waterfall and located in Peru.
[edit] See also
[edit] External links
[edit] References
- ^ Richard H. Beisel Jr., International Waterfall Classification System, Outskirts Press, 2006 ISBN 1598003402