Aeolian processes
Deposition

Wind is very effective at separating sand from silt and clay. As a result, there are distinct sandy (erg) and silty (loess) aeolian deposits, with only limited interbedding between the two. Loess deposits are found further from the original source of sediments than ergs. An example of this is the Sand Hills of Nebraska, US. Here vegetation-stabilized sand dunes are found to the west and loess deposits to the east, further from the original sediment source in the Ogallala Formation at the feet of the Rocky Mountains.

Some of the most significant experimental measurements on aeolian landforms were performed by Ralph Alger Bagnold, a British army engineer who worked in Egypt prior to World War II. Bagnold investigated the physics of particles moving through the atmosphere and deposited by wind. He recognized two basic dune types, the crescentic dune, which he called " barchan ", and the linear dune, which he called longitudinal or "seif" (Arabic for "sword"). Bagnold developed a classification scheme that included small-scale ripples and sand sheets as well as various types of dunes.

Bagnold's classification is most applicable in areas devoid of vegetation. In 1941, John Tilton Hack added parabolic dunes, which are strongly influenced by vegetation, to the list of dune types. The discovery of dunes on Mars reinvigorated aeolian process research, which increasingly makes use of computer simulation.

Wind-deposited materials hold clues to past as well as to present wind directions and intensities. These features help us understand the present climate and the forces that molded it. For example, vast inactive ergs in much of the modern world attest to late Pleistocene trade wind belts being much expanded during the Last Glacial Maximum. Ice cores show a tenfold increase in non-volcanic dust during glacial maxima. The highest dust peak in the Vostok ice cores dates to 20 to 21 thousand years ago. The abundant dust is attributed to a vigorous low-latitude wind system plus more exposed continental shelf due to low sea levels.

Wind-deposited sand bodies occur as ripples and other small-scale features, sand sheets, and dunes.
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