AY Honors/Waterfalls/Answer Key

A waterfall is a geological formation resulting from a stream flowing over an erosion-resistant rock formation that forms a sudden break in elevation.

Some waterfalls form in montane environments where erosion is rapid and stream courses may be subject to sudden and catastrophic change. In such cases, the existence of the waterfall may not be due to 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.

Most waterfalls are the result of many years' worth 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-resistent 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 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.

Notable waterfalls include:

• Angel Falls, the world's highest, in Venezuela in South America
• Iguaçu Falls, in South America, on the Iguaçu River on the border between Brazil and Argentina
• Victoria Falls, the world's largest, in Africa, on the Zambezi River on the border between Zambia and Zimbabwe
• Niagara Falls, the best-known in North America, located on the Niagara River on the border between New York, United States, and Ontario, Canada
• Cumberland Falls, the only waterfall in North America featuring a "moonbow"; located in southeast Kentucky
• Rhine Falls, Europe's largest, located in Switzerland