AY Honors/Waterfalls/Answer Key

For other uses see Waterfall (disambiguation)

Hopetoun Falls near Otway National Park, Victoria, Australia

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.

Some waterfalls form in mountain environments where erosion is rapid 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.

Waterfalls may also be artificial, and they are sometimes created as garden and landscape ornaments.

Formation

Formation of a waterfall

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 (also known as a rock house 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.

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 due to the kinetic energy of the water hitting the bottom.

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.

Types of waterfalls

Havasu Falls, near Supai, Arizona, is an example of a plunge waterfall

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Powerscourt Waterfall, near Enniskerry, Wicklow County, is an example of a horsetail waterfall

• Block: Water descends from a relatively wide stream or river.
• Cascade: Water descends a series of rock steps.
• Cataract: A large 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.

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See also

• Water feature

External links

• World Waterfall Database