Waterfalls are commonly formed when a river is young.At
these times the channel is often narrow and deep. When the river courses over
resistant bedrock, erosion happens slowly, while downstream
the erosion occurs more rapidly. As the
watercourse increases its velocity at the edge of the waterfall, it plucks
material from the riverbed. Whirlpools created in the turbulence as well as
sand and stones carried by the watercourse increase the erosion capacity. This
causes the waterfall to carve deeper into the bed and to recede upstream. Often
over time, the waterfall will recede back to form a canyon or gorge downstream
as it recedes upstream, and it will carve deeper into the ridge above it.The
rate of retreat for a waterfall can be as high as one and half meters per
Often, the rock stratumjust below the more resistant shelf will
be of a softer type, meaning that undercutting due to splashback will occur here
to form a shallow cave-like formation known as a rock shelter 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
battar george waterfall and Lebanon
Streams become wider and shallower just above waterfalls due to flowing over
the rock shelf, and there is usually a deep area 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. After a long period of
being fully formed, the water falling off the ledge will retreat, causing a
horizontal pit parallel to the waterfall wall. Eventually, as the pit grows
deeper, the waterfall collapses to be replaced by a steeply sloping stretch of
river bed. In
addition to gradual processes such as erosion, earth movement caused by earthquake or landslides or volcanoes can cause a differential in land
heights which interfere with the natural course of a water flow, and result in
A river sometimes flows over a large step in the rocks that may have been
formed by a fault line. Waterfalls can occur along the edge
of a glacial trough, where 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,
which is referred to as a hanging valley. Another reason hanging valleys
may form is where two rivers join and one is flowing faster than the other.
Waterfalls can be grouped into ten broad classes based on the average volume of
water present on the fall (which depends on both the waterfall's average flow
and its height) using a logarithmic scale. Class 10 waterfalls include Niagara Falls, Paulo Afonso Falls and Khone Falls.