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Sastrugi, or zastrugi, are features formed by
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
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 ridges.
Sastrugi are distinguished by upwind-facing points, resembling
anvil
An anvil is a metalworking tool consisting of a large block of metal (usually forged or cast steel), with a flattened top surface, upon which another object is struck (or "worked").
Anvils are as massive as practical, because the higher th ...
s, which move downwind as the surface erodes.
These points usually lie along ridges perpendicular to the prevailing wind;
they are steep on the
windward
Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...
side and sloping to the
leeward
Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...
side.
[ Smaller irregularities of this type are known as ]ripples
Ripple may refer to:
Science and technology
* Capillary wave, commonly known as ripple, a wave traveling along the phase boundary of a fluid
** Ripple, more generally a disturbance, for example of spacetime in gravitational waves
* Ripple (electri ...
(small, ~10 mm high) or wind ridges.
Large sastrugi are troublesome to ski
A ski is a narrow strip of semi-rigid material worn underfoot to glide over snow. Substantially longer than wide and characteristically employed in pairs, skis are attached to ski boots with ski bindings, with either a free, lockable, or partial ...
ers and snowboard
Snowboards are boards where the user places both feet, usually secured, to the same board. The board itself is wider than most skis, with the ability to glide on snow."snowboarding." Dictionary.com Unabridged (v 1.1). Random House, Inc. 17 Mar ...
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
The plural (sometimes abbreviated pl., pl, or ), in many languages, is one of the values of the grammatical category of number. The plural of a noun typically denotes a quantity greater than the default quantity represented by that noun. This de ...
s; the singular
Singular may refer to:
* Singular, the grammatical number that denotes a unit quantity, as opposed to the plural and other forms
* Singular homology
* SINGULAR, an open source Computer Algebra System (CAS)
* Singular or sounder, a group of boar, ...
is ''zastruga''. The form ''sastruga'' started as the German-language transliteration of the Russian word заструга (plural: заструги).[C. Fitzhugh Talman: ]
The singular of “sastrugi”
', Monthly Weather Review 43, February 1915, p. 85–86
A Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
-type analogical singular ''sastrugus'' is used in various writings on exploration of the South Pole, including Robert Falcon Scott
Captain Robert Falcon Scott, , (6 June 1868 – c. 29 March 1912) was a British Royal Navy officer and explorer who led two expeditions to the Antarctic regions: the ''Discovery'' expedition of 1901–1904 and the ill-fated ''Terra Nov ...
's expedition's diaries and Ernest Shackleton
Sir Ernest Henry Shackleton (15 February 1874 – 5 January 1922) was an Anglo-Irish Antarctic explorer who led three British expeditions to the Antarctic. He was one of the principal figures of the period known as the Heroic Age of ...
's '' The Heart of the Antarctic''.
Formation mechanism
Under the action of steady wind, free snow particles accumulate and drift like the sand grains in barchan
A barchan or barkhan dune (from Kazakh бархан ) is a crescent-shaped dune. The term was introduced in 1881 by Russian naturalist Alexander von Middendorf, based on their occurrence in Turkestan and other inland desert regions. Barchans ...
dune
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...
s, and the resulting drifting snow shapes are also popularly referred to as ''barchans''. Inuit
Inuit (; iu, ᐃᓄᐃᑦ 'the people', singular: Inuk, , dual: Inuuk, ) are a group of culturally similar indigenous peoples inhabiting the Arctic and subarctic regions of Greenland, Labrador, Quebec, Nunavut, the Northwest Territories ...
of Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
call them ''kalutoqaniq''. When winds slacken, the drifted formations consolidate via sublimation and 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.[Wonders, William C., ''Canada's changing North,'' Mcgill Queens Univ Press, 2003]
p. 40
/ref>
On sea ice
Sastrugi are more likely to form on first-year sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
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 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 pools of open water that form on sea ice in the warmer months of spring and summer. The ponds are also found on glacial ice and ice shelves. Ponds of melted water can also develop under the ice.
Melt ponds are usually darker tha ...
. Melt ponds are more likely to form in the depressions between sastrugi on first-year ice.
See also
* Cape Sastrugi
Cape Sastrugi () is a sharply projecting point on the west side of Deep Freeze Range, standing 1.5 nautical miles (2.8 km) northwest of Snowy Point and overlooking the north portion of Nansen Ice Sheet, in Victoria Land. First explored by th ...
* Cornice (snow)
A snow cornice or simply cornice (from the Italian cornice meaning "ledge") is an overhanging edge of snow on a ridge or the crest of a mountain and along the sides of gullies.
Formation
A snow cornice forms by wind blowing snow over sharp terr ...
* Föhn wind
A Foehn or Föhn (, , ), is a type of dry, relatively warm, downslope wind that occurs in the leeward, lee (downwind side) of a mountain range.
It is a rain shadow wind that results from the subsequent adiabatic warming of air that has dropped m ...
* Snowdrift
A snowdrift is a deposit of snow sculpted by wind into a mound during a snowstorm. Snowdrifts resemble sand dunes and are formed in a similar manner, namely, by wind moving light snow and depositing it when the wind has virtually stopped, u ...
References
*
* {{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 , isbn= 978-0-7867-0684-6 , url-access= registration , url= https://archive.org/details/heartofantarctic0000shac
Snow or ice weather phenomena
Aeolian landforms
Geography of the Arctic
Geography of Antarctica