A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.

Formation

Typically, a river flows 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. 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.

Waterfalls can occur along the edge of a 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.

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 Afonso 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, Lower Yellowstone Falls and Umphang Thee Lor Sue Waterfall (Class 6).

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.

left|220px|thumb|Frozen waterfall in southeast New York

• 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.

Examples of large waterfalls

Significant waterfalls are listed alphabetically:

• Angel Falls is the world's tallest 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 tallest waterfall in England.

• Colonial Creek Falls, the second tallest waterfall in North America at 2,584 ft (788 m), is located in the North Cascades National Park, Washington, United States.

• Dettifoss, 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 100 m wide and have a drop of 44 m down to the Jökulsárgljúfur canyon.

• Eas a' Chual Aluinn, at 200 m (658 ft), is the tallest waterfall in both Scotland and the United Kingdom.

• Gocta is the fifth tallest 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 is a tall and extremely wide waterfall located in South America on the Argentina/Brazil border.

• James Bruce Falls, the tallest waterfall in North America at 840 m, is located in the Princess Louisa Marine Provincial Park, British Columbia, Canada.

• Jog Falls is India's tallest (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 high and 30 ft wide.

• Niagara Falls are the most powerful falls in North America.

• Pissing Mare Falls, at 350 m (1148 ft), is the tallest in eastern North America.

• Pistyll Rhaeadr, the tallest waterfall in Wales at 240ft (73m).

• Ramnefjellsfossen is the world's third tallest at 808 m (2685 ft), at Stryn, Nesdalen, Norway.

• Rhine Falls is Europe's widest and is 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.

• Swallow Falls is one of Wales's largest waterfalls.

• Takakkaw Falls is a 384 m (1260 feet) in Yoho National Park in Canada.

• Tequendama Falls is a 132 m high waterfall on the Bogotá River, about 30 km southwest of Bogotá in Colombia.

• Tugela Falls is the world's second tallest 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.

• 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, the tallest waterfall in the United States at 2,600 ft (792 m), is located in the Waimanu Valley, Hawaii, United States.

• Yosemite Falls, the fourth tallest waterfall 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.

See also

right|thumb|Plitvice lakes, Croatia

• Stream pool

• Water feature

• Tributary