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{{short description|Sharp irregular grooves or ridges formed on a snow surface}}
[[File:Anta0183 (19778502135).jpg|300px|thumb|Wind sculpted snow near South Pole Station, forming sastrugi features.]]
'''Sastrugi''', or '''zastrugi''', are features formed by the [[erosion]] of snow by wind. 
They are found in polar regions, and in snowy, wind-swept areas of temperate regions, such as frozen lakes or [[mountain ridge]]s.<ref name="mountain ridges">{{Cite journal|last1=Kochanski|first1=K.|last2=Anderson|first2=R.S.|last3=Tucker|first3=G.|date=Jun 2018|title=Statistical classification of self-organized snow surfaces|journal=Geophysical Research Letters|volume=45|issue=13|pages=6532–6541|doi=10.1029/2018GL077616|bibcode=2018GeoRL..45.6532K |osti=1539740|doi-access=free|url=https://repository.library.noaa.gov/view/noaa/26516/noaa_26516_DS1.pdf}}</ref> 
Sastrugi are distinguished by upwind-facing points, resembling [[anvil]]s, which move downwind as the surface erodes.<ref name="move">{{Cite journal|last1=Kochanski|first1=K.|last2=Anderson|first2=R.S.|last3=Tucker|first3=G.|date=2019|title=The evolution of snow bedforms in the Colorado Front Range|journal=The Cryosphere|volume=13|pages=1267–1281|doi=10.5194/tc-13-1267-2019|doi-access=free}}</ref> 
These points usually lie along ridges parallel to the prevailing wind;<ref name="parallel">{{Cite journal|last1=Leonard|first1=K. C.|last2=Tremblay|first2=B.|date=Dec 2006|title=Depositional origin of snow sastrugi|journal=AGU Fall Meeting Abstracts|volume=2006|pages=C21C–1170|bibcode=2006AGUFM.C21C1170L|id=#C21C-1170}}</ref> they are steep on the [[Windward and leeward|windward]] side and sloping to the [[Windward and leeward|leeward]] side.<ref name=talman/> Smaller irregularities of this type are known as [[ripple marks|ripples]] (small, ~10&nbsp;mm high) or wind ridges.

Large sastrugi are troublesome to [[ski]]ers and [[snowboard]]ers. Traveling on the irregular surface of sastrugi can be very tiring and can risk breaking equipment; ripples and waves are often undercut, and the surface is hard and unforgiving, with constant minor topographic changes between ridge and trough.

== Etymology ==
The words ''sastrugi'' and ''zastrugi'' are Russian-language [[plural]]s; the [[Grammatical number|singular]] is ''zastruga''. The form ''sastruga'' started as the German-language transliteration of the Russian word заструга (plural: заструги).<ref name=talman>C. Fitzhugh Talman: ''[http://docs.lib.noaa.gov/rescue/mwr/043/mwr-043-02-0085.pdf The singular of “sastrugi”]'', Monthly Weather Review 43, February 1915, p. 85–86</ref>

A [[Latin]]-type analogical singular ''sastrugus'' is used in various writings on exploration of the South Pole, including [[Robert Falcon Scott]]'s expedition's diaries and [[Ernest Shackleton]]'s ''[[The Heart of the Antarctic]]''.

== Formation mechanism ==
[[File:Lake Vostok Sat Photo color.jpg|464px|thumb|Large sastrugi seen in radar image around the south edge (left side) of [[Lake Vostok]] in Antarctica ([[RADARSAT]], [[NASA]]). White and black colors on sastrugi are not lights and shadows; they demonstrate a difference in radioreflectivity of snow deposits on the windward and leeward sides of a sastruga.]]

Under the action of steady wind, free snow particles accumulate and drift like the sand grains in [[barchan]] [[dune]]s, and the resulting drifting snow shapes are also popularly referred to as ''barchans''. [[Inuit]] of [[Canada]] call them ''kalutoqaniq''. When winds slacken, the drifted formations consolidate via [[Sublimation (phase transition)|sublimation]] and [[Recrystallization (geology)|recrystallization]]. Subsequent winds erode kalutoqaniq into the sculptured forms of sastrugi. Inuit call large sculpturings ''kaioqlaq'' and small ripples ''tumarinyiq''. Further erosion may turn ''kaioqlaq'' back into drifting ''kalutoqaniq''. An intermediate stage of erosion is ''mapsuk'', an overhanging shape. On the windward side of a ridge, the base erodes faster than the top, producing a shape like an anvil tip pointing upwind.<ref name= wonders>Wonders, William C., ''Canada's changing North,'' Mcgill Queens Univ Press, 2003 {{ISBN|978-0773526402}} [https://books.google.com/books?id=PHsyINzEEgEC&dq=zastrugi&pg=PA40 p. 40]</ref>

== On sea ice ==

Sastrugi are more likely to form on first-year [[sea ice]] than on multiyear ice. First-year ice is smoother than multiyear ice, which allows the wind to pass uniformly over the surface without topographic obstructions. Except during the melt season, snow  is dry and light in climates cold enough for sea ice, allowing the snow to be easily blown and create sastrugi parallel<ref name="parallel" /><ref name="parallel2">{{cite web |url= http://www.hko.gov.hk/prtver/html/docs/education/edu01met/01met_antarctic/ele_sastrugi_e.shtml |title= Sastrugi |first= John K.W. |last= Chan |publisher= Hong Kong Observatory (HKO) }}</ref> to the wind direction. The locations of sastrugi are fixed by March in the northern hemisphere and may be linked to the formation of [[melt ponds]]. Melt ponds are more likely to form in the depressions between sastrugi on first-year ice.<ref>{{cite journal |last1= Petrich |first1= C. |first2= H. |last2= Eicken |first3= C. M. |last3= Polashenski |first4= M. |last4= Sturm |first5= J. P. |last5= Harbeck |first6= D. K. |last6= Perovich |first7= D. C. |last7= Finnegan |date= 25 Sep 2012 |title= Snow dunes: A controlling factor of melt pond distribution on Arctic sea ice |journal= J. Geophys. Res. |volume= 117 |issue= C09029 |pages= C09029 |doi= 10.1029/2012JC008192 |bibcode= 2012JGRC..117.9029P |hdl= 2060/20140011040 |hdl-access= free }}</ref>

== See also ==
* [[Cape Sastrugi]]
* [[Cornice (snow)]]
* [[Föhn wind]]
* [[Snowdrift]]

== References ==
{{reflist}}
* {{cite book |editor-last1= Grey |editor-first1= D. M. |editor-last2= Male |editor-first2= D. H. |date= 2004 |title= Handbook of Snow: Principles, Processes, Management and Use |publisher= Blackburn Press |isbn= 978-1-932846-06-5 }}
* {{cite book |last= Shackleton |first= Sir Ernest Henry |date= 1909 |title= The Heart of the Antarctic: Being the Story of the British Antarctic Expedition, 1907-1909 |publisher= Basic Books |isbn= 978-0-7867-0684-6 |url-access= registration |url= https://archive.org/details/heartofantarctic0000shac }}

[[Category:Snow or ice weather phenomena]]
[[Category:Aeolian landforms]]
[[Category:Geography of the Arctic]]
[[Category:Geography of Antarctica]]