Zastruga

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Sastrugi at the South Pole.

Sastrugi, or zastrugi, are sharp irregular grooves or ridges formed on a snow surface by wind erosion, saltation of snow particles, and deposition, and found in polar and temperate snow regions. They differ from sand dunes in that the ridges are markedly parallel to the prevailing winds. Smaller irregularities of this type are known as ripples (small, ~10 mm high), or wind ridges.

Larger features are especially troublesome to skiers and snowboarders. Traveling on the irregular surface of sastrugi can be very tiring, and can risk breaking equipment—ripples and waves are often undercut, the surface is hard and unforgiving with constant minor topographic changes between ridge and trough.

Etymology

The words sastrugi/zastrugi are Russian-language plurals: the singular is sastruga or zastruga. The form sastruga is the German-language transliteration of Russian: Заструга.[1]

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

Formation mechanism

Under the wind, free snow particles accumulate and drift similarly to barchan dunes of sand, and the resulting drifting snow shapes are also popularly referred to as barchans. Inuit of Canada call them kalutoqaniq. When winds slacken, barchans/kalutoqaniq consolidate via sublimation and recrystallization. Subsequent winds erode kalutoqaniq into sculptured forms of zastrugi. Inuit call large sculpturings kaioqlaq and the small ripples tumarinyiq. Further erosion may turn kaioqlaq back into a drifting kalutoqaniq. An intermediate stage of erosion is mapsuk, an overhanging shape. At the windward end of a ridge, the base erodes faster than above, producing a recognizable shape of anvil tip pointing upwind.[2]

Zastrugi on sea ice

Zastrugi are more likely to form on first-year sea ice as opposed to multiyear ice. First-year ice is smoother than multiyear ice that allows the wind to pass uniformly over the surface without topographic obstructions. Except for the melt season, snow is dry and light allowing it to be easily blown and create zastrugi parallel to the wind direction. It has been shown that the location of zastrugi are fixed by March and may be linked to the formation of melt ponds. Melt ponds are more likely to form in the depressions between zastrugi on first year ice.[3]

See also

References

  1. ↑ Rapport du Comité consultatif: Report of the Advisory committee, Google books
  2. ↑ Wonders, William C., Canada's changing North, Mcgill Queens Univ Press, 2003 ISBN 978-0773526402 p. 40
  3. ↑ Petrich, C., H. Eicken, C. M. Polashenski, M. Sturm, J. P. Harbeck, D. K. Perovich, and D. C. Finnegan (2012), Snow dunes: A controlling factor of melt pond distribution on Arctic sea ice, J. Geophys. Res., 117, C09029, doi:10.1029/2012JC008192.
  • Grey, D. M. & Male, D. H. (editors). (2004). Handbook of Snow: Principles, Processes, Management and Use. ISBN 1-932846-06-9
  • Shackleton, Sir Ernest Henry. (1909) The Heart of the Antarctic: Being the Story of the British Antarctic Expedition, 1907-1909 ISBN 978-0-7867-0684-6
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