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yardang
A yardang is a streamlined protuberance carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion by dust and sand, and deflation which is the removal of loose material by wind turbulence.〔(Desert Processes Working Group: Yardangs ) 〕 Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of a boat. Facing the wind is a steep, blunt face that gradually gets lower and narrower toward the lee end. Yardangs are formed by wind erosion, typically of an originally flat surface formed from areas of harder and softer material. The soft material is eroded and removed by the wind, and the harder material remains. The resulting pattern of yardangs is therefore a combination of the original rock distribution, and the fluid mechanics of the air flow and resulting pattern of erosion.
==Etymology==
The word itself is of Turkic origin,〔"yardang." ''Webster's Third New International Dictionary, Unabridged''. Merriam-Webster, 2002. (''web link'' )〕〔"yardang." ''Dictionary.com Unabridged (v 1.1)''. Random House, Inc. 12 Mar. 2008. (''web link'' )〕 meaning ‘steep bank’, and was first introduced to the English-speaking world by the Swedish explorer Sven Anders Hedin in 1903.〔Hedin, S.A. (1903) (''Central Asia and Tibet'' ), 2 vols, pp. 608, New York and London: Charles Scribner and Sons〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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