US Geological Survey


Date of this Version



In: Encyclopedia of Geology, 2nd edition, Alderton & Elias, eds. (Academic Press, 2021) v.5, pp.34-369.


U.S. government work


Eolian (windblown) sediments form some of the world’s most dramatic landscapes and comprise important parts of the geologic record. This article reviews the characteristics, origins, and significance of eolian deposits, including windblown sand, silt, and dust.

Landforms composed of eolian sand, either as dunes or sand sheets, occupy substantial areas over the surface of the Earth (perhaps as much as 6% globally, but over ~20% of the world’s arid zones, according to Pye and Tsoar, 2009). Low-latitude arid or semiarid regions, usually under the influence of subtropical high-pressure cells, are some of the largest areas of eolian sand accumulation (Lancaster, 1995; Pye and Tsoar, 2009). Active dune fields exist over large areas of the planet today (Fig. 1). Similar sand seas existed in deeper geologic time, too, throughout much of the Paleozoic and Mesozoic, and provide valuable clues about paleoclimate at these earlier times in the Earth’s history.

Loess is eolian silt that typically mantles pre-existing topography and is thick enough to form a recognizable unit when observed in the field. Reviews of loess can be found in Pye (1987) and Muhs (2013a). As much as 10% of the Earth’s present land surface may be covered by loess, primarily in mid-latitude regions, notably in Asia, Europe, South America, and North America (Figs. 2 and 3). Smaller areas of loess are found in New Zealand, Australia, Japan, the Middle East and North Africa. Loess provides a valuable Quaternary stratigraphic record, with intercalated buried soils (paleosols) generally recording interglacial periods and loess typically recording glacial periods. Much loess, in fact, is of a glaciogenic origin. Glaciers are very efficient producers of silt, or “rock flour,” as they traverse landscapes. Loess is now recognized in the pre-Quaternary rock record as well, and may have been the source material for many siltstones in the geologic record.