AY Honors/Waterfalls/Answer Key

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. Waterfalls may also be artificial, and they are sometimes used for garden and landscape ornament.

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 thrust faults or volcanic action.

Formation

Formation of a waterfall

Some waterfalls are the result of action of water on the underlying strata. Typically, a stream will flow across an area of formations, and more resistant rock strata will form shelves across the streamway, elevated above the further stream bed when the less erosion-resistant rock around it disappears. Over a period of years, the edges of this shelf will gradually break away and the waterfall will steadily move upstream. Often, the rock strata just below the more resistant shelf will be of a softer type, and will erode out to form a shallow cave-like formation known as a rock shelter (also known as a rock house) under and behind the waterfall.

Streams often 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.

Types of waterfalls

Cascade-style waterfall in Oregon, United States.

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.

Examples of large waterfalls

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Angel Falls, the world's highest at 979 m (3230 ft), in Venezuela
Victoria Falls, the world's largest, on the Zambezi River, on the border between Zambia and Zimbabwe
Boyoma Falls, with the world's highest volume, 17,000 m³/s (600,000 ft³/s), on the Congo River, Democratic Republic of the Congo
Yosemite Falls, the tallest in North America, located in Yosemite National Park, United States
Niagara Falls, most voluminous in North America, on the border between the United States and Canada
Rhine Falls, Europe's largest, located in Switzerland
Iguazu Falls, a tall and extremely wide fall located in South America on the Argentina/Brazil border
Jog Falls, India's highest and second highest in Asia, located in Karnataka state, India
Jurong Falls in Singapore is said to be the tallest man-made waterfall in the world