waterfall

waterfall

[waw-ter-fawl, wot-er-]
waterfall, a sudden unsupported drop in a stream. It is formed when the stream course is interrupted as when a stream passes over a layer of harder rock—often igneous—to an area of softer and therefore more easily eroded rock; the edge of a cliff or plateau; or the edge of a hanging valley formed under glacial conditions (see glacial periods). Normally, as a stream grows older, the waterfall, by undercutting and erosion of the waterfall edge and stream bed above the fall, moves upstream and loses height until it eventually becomes a series of rapids and finally disappears. Waterfalls are often a source of waterpower for cities such as the string of cities in the United States that grew up along the waterfall line where streams from the Appalachians descend suddenly to the coastal plain and early textile and flour mills used power from waterfalls. Angel Falls in Venezuela is the world's highest waterfall.

Area where flowing river water drops abruptly and nearly vertically. A waterfall may also be termed a falls, or, when large volumes of water are involved, a cataract. Waterfalls of small height and less steepness or a series of small falls are called cascades. Still gentler stretches of river that exhibit turbulent flow and white water are called rapids.

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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 sudden break in elevation or nickpoint.

Some waterfalls form in mountain environments where 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 in the winter snow will build up. And when summer come it melts and turns into a water fall

Formation

Typically, a river flows over a large step in the rocks which may have been formed by a fault line. Over a period of years, the edges of this shelf will gradually break away and the waterfall will steadily retreat upstream, creating a gorge of recession. Often, the rock stratum just below the more resistant shelf will be of a softer type, meaning 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 more shallow 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.

Classifying Waterfalls

Waterfalls are grouped into 10 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).

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, 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 include these alphabetically:

See also

References

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