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 created as 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.
Typically, a stream flow across an area of formations 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.
Waterfalls can also form due to glaciation, 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.
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.
Turning Off Niagara Falls Could Reveal Geological Secrets Live Science - February 9, 2016
For the first time in nearly 50 years, officials are debating turning off the tap for part of Niagara Falls. Officials have proposed drying out two of the three waterfalls that make up Niagara Falls - American Falls and Bridal Veil Falls - so that workers can repair the aging pedestrian bridges that span the rapids along the river that feeds the falls. Horseshoe Falls is the third waterfall that makes up Niagara. The proposed "dewatering" would do more than provide the curious with a rare chance to see the landscape transformed. It could also yield unprecedented insights into the rock-cutting process that is hidden beneath the flow of millions of gallons of water. Niagara Falls are "very spectacular aesthetically, but they're not studied a lot geologically," said Marcus Bursik, a geologist with the University at Buffalo, who is proposing to measure some of the changes in the falls if the water is cut off. The new plan could provide a one-time chance to do some of that geological research.
Gallery: Most Famous Waterfalls in the US Live Science - May 31, 2013
Waterfalls have an irresistible draw on the American public. Whether people want to photograph them or ride over them in barrels, the rushing water has an indomitable, captivating power. The United States is rich with famous waterfalls. From world-renowned names to little-known cult favorites, and from roaring falls to scenic trickles, there are waterfalls in every state in the Union. Here are the most famous falls that America has to offer.
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