Editing Waterfall (section)

=== Caprock model ===
The caprock model of waterfall formation{{Sfn|Goudie|2020|p=63}} states that the river courses over resistant [[bedrock]], erosion happens slowly and is dominated by impacts of water-borne sediment on the rock, while downstream the erosion occurs more rapidly.<ref name="fenh" /><ref name="howstuff">{{cite web|url=http://geography.howstuffworks.com/terms-and-associations/waterfall.htm/printable|title=How Waterfalls Work |first1=John |last1=Fuller |website=Howstuffworks |date=16 June 2008|access-date=10 November 2016|archive-date=21 September 2010|archive-url=https://web.archive.org/web/20100921080941/http://geography.howstuffworks.com/terms-and-associations/waterfall.htm/printable}}</ref> As the watercourse increases its velocity at the edge of the waterfall, it may pluck material from the riverbed, if the bed is fractured or otherwise more erodible. Hydraulic jets and hydraulic jumps at the toe of a falls can generate large forces to erode the bed,<ref>{{Cite journal|last1=Pasternack|first1=Gregory B.|last2=Ellis|first2=Christopher R.|last3=Marr|first3=Jeffrey D.|date=1 July 2007|title=Jet and hydraulic jump near-bed stresses below a horseshoe waterfall |bibcode-access=free |s2cid-access=free |journal=Water Resources Research|language=en|volume=43|issue=7|pages=W07449|doi=10.1029/2006wr005774|bibcode=2007WRR....43.7449P|s2cid=64365663|issn=1944-7973|url=http://www.escholarship.org/uc/item/8460z7p8|access-date=26 January 2019|archive-date=21 February 2019|archive-url=https://web.archive.org/web/20190221224121/https://escholarship.org/uc/item/8460z7p8|url-status=live|doi-access=free}}</ref> especially when forces are amplified by water-borne sediment. Horseshoe-shaped falls focus the erosion to a central point, also enhancing riverbed change below a waterfall.<ref>{{Cite web|url=http://pasternack.ucdavis.edu/research/projects/waterfalls/horseshoe-falls/|title= Watershed Hydrology, Geomorphology, and Ecohydraulics :: Horseshoe Falls|website=Dr. Gregory B. Pasternack |language=en|access-date=11 June 2017|archive-date=25 August 2017|archive-url=https://web.archive.org/web/20170825234342/http://pasternack.ucdavis.edu/research/projects/waterfalls/horseshoe-falls/|url-status=live}}</ref>

A process known as "potholing" involves local erosion of a potentially deep hole in bedrock due to turbulent [[whirlpool]]s spinning stones around on the bed, drilling it out. Sand and stones carried by the watercourse therefore increase erosion capacity.<ref name="fenh" /> 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.<ref name="visual">{{cite web|url=http://www.classzone.com/books/earth_science/terc/content/visualizations/es1305/es1305page01.cfm?chapter_no=visualization|title=Observe river erosion creating waterfalls and chasms.|access-date=10 November 2016|archive-date=17 May 2015|archive-url=https://web.archive.org/web/20150517030906/http://www.classzone.com/books/earth_science/terc/content/visualizations/es1305/es1305page01.cfm?chapter_no=visualization|work=Exploring Earth |publisher=ClassZone }}</ref> The rate of retreat for a waterfall can be as high as one-and-a-half metres per year.<ref name="fenh" />

Often, the rock [[stratum]] just 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 [[outcrop]]ping, 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 (erosion)|attrition]] as they collide with each other, and they also erode the base of the waterfall by [[Abrasion (geology)|abrasion]], creating a deep [[plunge pool]] in the gorge downstream.<ref name=":3" />

Streams can 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. However, a study of waterfalls systematics reported that waterfalls can be wider or narrower above or below a falls, so almost anything is possible given the right geological and hydrological setting.<ref name=":0">{{Cite journal|last1=Wyrick|first1=Joshua R.|last2=Pasternack|first2=Gregory B.|date=1 September 2008|title=Modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps|journal=Journal of Geophysical Research: Earth Surface|language=en|volume=113|issue=F3|pages=F03003|doi=10.1029/2007jf000873|bibcode=2008JGRF..113.3003W|issn=2156-2202|url=http://www.escholarship.org/uc/item/98m7s64p|access-date=26 January 2019|archive-date=13 September 2019|archive-url=https://web.archive.org/web/20190913180502/https://escholarship.org/uc/item/98m7s64p|url-status=live}}</ref>{{Original research inline|date=July 2024}} 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.<ref name="fenh"/> In addition to gradual processes such as erosion, earth movement caused by [[earthquake]]s or [[landslide]]s or [[volcano]]es can lead to the formation of waterfalls.<ref name=":3" />