A plunge pool (or plunge basin or waterfall lake) is a deep depression in a stream bed at the base of a

waterfall A waterfall is a point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in several wa ...

or shut-in. It is created by the erosional forces of cascading water on the rocks at formation's base where the water impacts.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. The term may refer to the water occupying the depression, or the depression itself.

Formation

Plunge pools are formed by the natural force of falling water, such as at a

or cascade; they also result from man-made structures such as some

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

designs. Plunge pools are often very deep, generally related to the height of fall, the volume of water, the resistance of the rock below the pool and other factors. The impacting and swirling water, sometimes carrying rocks within it, abrades the riverbed into a basin, which often features rough and irregular sides. Plunge pools can remain long after the waterfall has ceased flow or the stream has been diverted. Several examples of former plunge pools exist at

Dry Falls Dry Falls is a scalloped precipice with four major alcoves, in central Washington scablands. This cataract complex is on the opposite side of the Upper Grand Coulee from the Columbia River, and at the head of the Lower Grand Coulee, northern ...

in the

Channeled Scablands The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods ...

of eastern

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

. The Channeled Scablands of Eastern Washington: the geologic story of the Spokane flood
p.18-19

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

(1973) They can also be found underwater in areas that were formerly above sea level, for example

Perth Canyon Perth Canyon is a submarine canyon located on the edge of the continental shelf off the coast of Perth, Western Australia, approximately west of Rottnest Island. It was carved by the Swan River, probably before the Tertiary, when this part of t ...

off the coast of

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

. Plunge pools are

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

features of erosion which occur in the youthful stage of river development, characterized by steeper

gradients In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the grad ...

and faster water flows. Where softer or fractured rock has been eroded back to a

knickpoint In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous e ...

, water continues to bombard its base. Because this rock is often less resistant than overlying strata, the water from the higher elevation continues eroding downward until an equilibrium is achieved. A somewhat similar bowl-shaped feature developed by flowing water, as opposed to falling water, is known as a scour hole. These occur both naturally and as a result of

bridge building A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

References

External links

USGS: Stream Modeling website
{{Rivers, streams and springs Bodies of water Erosion landforms Fluvial landforms Garden features Geomorphology Hydrology Natural pools Swimming pools Water streams

Formation

See also

References

External links