Editing Ventifact (section)

{{short description|Rock that has been eroded by wind-driven sand or ice crystals}}
{{refimprove|date = April 2019}}
A '''ventifact''' (also '''wind-faceted stone''', '''windkanter'''<ref>Klaus K. E. Neuendorf, ''Glossary of Geology'', [https://books.google.com/books?id=yD79FqfECCYC&pg=PA723 p. 723]</ref>) is a [[rock (geology)|rock]] that has been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals.<ref>{{cite book|first=Julie E. |last=Laity |chapter=19. Landforms, landscapes, and processes of aeolian erosion |editor-last=Parsons|editor-first=Anthony J.|title=Geomorphology of desert environments|date=2009|publisher=Springer|location=[Dordrecht]|isbn=978-1402057199|pages=597–628|edition=2nd.|editor2-last=Abrahams |editor2-first=Athol D.}}</ref> The word "Ventifact" is derived from the [[Latin]] word "Ventus" meaning '[[wind]]'. These geomorphic features are most typically found in arid environments where there is little [[vegetation]] to interfere with [[aeolian processes|aeolian]] particle transport, where there are frequently strong [[winds]], and where there is a steady but not overwhelming supply of [[sand]].

[[File:Weisse Wüste.jpg|thumb|right|Wind-carved "[[mushroom]]" shaped rocks are the centerpiece of [[White Desert National Park]], [[Egypt]]]]
Ventifacts can be [[Abrasion (geology)|abraded]] to eye-catching natural sculptures such as the main features of the [[White Desert National Park]] near [[Farafra Oasis]] in [[Egypt]]. In moderately tall, isolated rock outcrops, [[mushroom]]-shaped pillars of [[Rock (geology)|rock]] may form as the outcrop is eroded by [[Saltation (geology)|saltating]] sand grains. This occurs because, even in strong [[winds]], [[sand]] grains cannot be continuously held in the [[air]]. Instead, the [[particles]] bounce along the ground, rarely reaching higher than a few feet above the [[Earth]]. Over time, the bouncing [[sand]] grains can erode the lower portions of a ventifact, while leaving a larger, less-eroded cap. The resulting forms thus frequently resemble fantastical [[stone]] [[mushrooms]].

Individual stones, such as those forming [[desert pavement]], are often found with grooved, etched, or polished [[surface]]s where these same wind-driven processes have slowly worn away the [[Rock (geology)|rock]]. 

Ventifacts are typically of three types:
* '''Einkanters''' having one polished side (excluding the bottom part) (the [[German language|German]] word 'ein' means 'one')
* '''Zweinkanters''' having two polished sides (excluding the bottom part) (the [[German language|German]] word 'zwei' means 'two')
* '''Dreinkanters''' having three polished surface (excluding the polished surface at bottom) that meet up at sharp angles (the [[German language|German]] word 'drei' means 'three')<ref>{{Cite book |last=Livingstone |first=Ian |title=Aeolian geomorphology: an introduction |last2=Warren |first2=Andrew |date=1996 |publisher=Longman |isbn=978-0-582-08704-0 |location=Harlow}}</ref> 

When ancient ventifacts are preserved without being moved or disturbed, they may serve as a paleo-[[wind]] indicators. The wind direction at the time the ventifact formed will be parallel to grooves or [[Striation (geology)|striations]] cut into the [[Rock (geology)|rock]]. 

Ventifacts have also been discovered on [[Mars]], where such sharp immobile [[rocks]] have caused significant damage to the wheels of the [[Curiosity (rover)|''Curiosity'' rover]].<ref name=llis>NASA, [https://llis.nasa.gov/lesson/22401 Premature Wear of the MSL Wheels], 2017-09-26</ref> An example of a [[Mars|Martian]] ventifact was named [[Jake Matijevic (rock)|Jake Matijevic]]. By analyzing its shape, it was possible to reconstruct the main [[wind]] direction which sculpted the [[Rock (geology)|rock]].<ref name="PZ13">Patrick Zasada (2013) ''Entstehung des Mars-Gesteins "Jake Matijevic"''. [http://www.sternzeit-online.de/ Sternzeit], [http://www.sternzeit-online.de/?p=archiv&q=2%2F2013 issue 2/2013]: pp. 98–101. (German language).</ref>

<gallery widths="200px">
file:Mendenhall 1905 USGS.jpg|[[Schist]] boulder pitted by sand blast near Palm Springs Station, [[Colorado Desert]]. [[Riverside County]], [[California]] (Mendenhall, 1905)
file:VentifactMojaveDesert031511.jpg|Ventifact from the [[Mojave Desert]] near [[Barstow, California|Barstow]], [[California]].
file:Ventifact_at_Ventifact_Ridge_in_Death_Valley.jpg|Ventifact at Ventifact Ridge in [[Death Valley]] (Mayer, 2003)
file:Bradley_1930_dreikanter.jpg|[[Granite]] dreikanter polished by windblown sand, [[Sweetwater County]], Wyoming ([[W. H. Bradley|Bradley]], 1930)
file:Segerstrom_1962_USGSProPaper450C.jpg|Outcrop of [[granite]] that has been undercut by the abrasive action of windblown sand, Llano de [[Caldera]], [[Atacama Desert|Atacama]] Province, [[Chile]] (Segerstrom, 1962)
file:Yardang Lea-Yoakum Dunes.jpg|Wind-carved, [[sandstone]] [[yardang]] in a [[Blowout (geology)|blowout]] near [[Meadow, Texas]] (Stout, 2002)
file:Im Salar de Uyuni.jpg|The [[Árbol de Piedra]] is a 7-metre-tall ventifact in the [[Altiplano]] region of [[Bolivia]] (Wilken, 2002).
</gallery>