Loess

Loess (pronunciation: /ˈloʊ.əs/, /ˈlʌs/, /ˈlɛs/, or UK /ˈlɜːrs/; from German Löss [lœs]) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. It covers about 10% of the Earth's surface.

Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs.

The word loess, with connotations of origin by wind-deposited accumulation, came into English from German Löss ([lœs]), which can be traced back to Swiss German and is cognate with the English word loose and the German word los. It was first applied to Rhine River valley loess about 1821.

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