View source for Plunge pool

{{Short description|Depression at the base of a waterfall}}
{{for|the small swimming pool|Swimming pool#Private pools}}
[[File:Seljalandsfoss plungepool.jpg|thumb|Surface of the [[Seljalandsfoss]] plunge pool (Iceland)]]
[[File:Plunge pool.png|thumb|Water going over the falls carries sand and pebbles that scour a plunge pool at its base.]]

A '''plunge pool''' (or '''plunge basin''' or '''waterfall lake''') is a deep depression in a stream bed at the base of a [[waterfall]] or [[Shut-in (river)|shut-in]]. It is created by the [[erosion|erosional]] forces of cascading water on the rocks at the formation's base where the water impacts.<ref name=EG>Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. {{ISBN|978-0393196566}}</ref> The term may refer to the water occupying the depression, or the depression itself.<ref>Robert L Bates, Julia A Jackson, ed. ''Dictionary of Geological Terms: Third Edition'',  p. 391, [[American Geological Institute]] (1984)</ref>

==Formation==

Plunge pools are formed by the natural force of  falling water, such as at a [[waterfall]] or cascade; they also result  from man-made structures such as some [[spillway]] designs.<ref>[https://books.google.com/books?id=x66ppt1lkHoC&pg=PA105 The Management of the Zambezi River Basin and Kariba Dam], p. 105 (2010)</ref> Plunge pools  are often very deep, generally related to the height of the fall, the volume of water, the resistance of the rock below the pool and other factors.<ref>Vincent J. Zipparro, Hans Hasen, [https://books.google.com/books?id=JIJUAAAAMAAJ&q=plunge+pool Davis' Handbook of Applied Hydraulics], p. 16.46 (1993)</ref> The impacting and swirling water, sometimes carrying rocks within it, [[Abrasion (geology)|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]] in the [[Channeled Scablands]] of eastern [[Washington (state)|Washington]].<ref>[https://pubs.usgs.gov/gip/70007447/report.pdf  The Channeled Scablands of Eastern Washington: the geologic story of the Spokane flood ], p.18-19 [[United States Geological Survey]] (1973)</ref> They can also be found underwater in areas that were formerly above sea level, for example, [[Perth Canyon]] off the coast of [[Western Australia]].

Plunge pools are [[fluvial]] features of [[erosion (geology)|erosion ]] which occur in the [[cycle of erosion|youthful stage]] of river development, characterized by steeper [[Stream gradient|gradients]] and faster water flows. Where softer or fractured rock has been eroded back to a [[knickpoint]], 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 scour|bridge building]].

==See also==
{{Portal|Environment}}
*[[Stream pool]]
*{{annotated link|List of waterfalls by flow rate}}
*{{annotated link|List of waterfalls by type}}
*{{annotated link|Riffle}}
*{{annotated link|Tinaja}}

==References==
{{Reflist}}

==External links==
*[https://web.archive.org/web/20100527194434/http://smig.usgs.gov/SMIG/features_0300/otis_fs.html USGS: Stream Modeling website]

{{Pond}}
{{River morphology}}
{{Rivers, streams and springs}}

[[Category:Bodies of water]]
[[Category:Erosion landforms]]
[[Category:Fluvial landforms]]
[[Category:Garden features]]
[[Category:Geomorphology]]
[[Category:Hydrology]]
[[Category:Natural pools]]
[[Category:Swimming pools]]
[[Category:Water streams]]