ventifact

{{short description|Rock that has been eroded by wind-driven sand or ice crystals}}

{{refimprove|date = April 2019}}

A ventifact (also wind-faceted stone, windkanterKlaus K. E. Neuendorf, Glossary of Geology, [https://books.google.com/books?id=yD79FqfECCYC&pg=PA723 p. 723]) is a rock that has been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals.{{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.}} 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 particle transport, where there are frequently strong winds, and where there is a steady but not overwhelming supply of sand.

File:Weisse Wüste.jpg" shaped rocks are the centerpiece of White Desert National Park, Egypt]]

Ventifacts can be 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 may form as the outcrop is eroded by 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 surfaces where these same wind-driven processes have slowly worn away the rock.

Ventifacts are typically of three types:

• Einkanters having one polished side (excluding the bottom part) (the German word 'ein' means 'one')
• Zweinkanters having two polished sides (excluding the bottom part) (the German word 'zwei' means 'two')
• Dreinkanters having three polished surface (excluding the polished surface at bottom) that meet up at sharp angles (the German word 'drei' means 'three'){{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}}

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 striations cut into the rock.

Ventifacts have also been discovered on Mars, where such sharp immobile rocks have caused significant damage to the wheels of the Curiosity rover.NASA, [https://llis.nasa.gov/lesson/22401 Premature Wear of the MSL Wheels], 2017-09-26 An example of a Martian ventifact was named Jake Matijevic. By analyzing its shape, it was possible to reconstruct the main wind direction which sculpted the rock.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).

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.

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 (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 Province, Chile (Segerstrom, 1962)

file:Yardang Lea-Yoakum Dunes.jpg|Wind-carved, sandstone yardang in a 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).