Research in the field of eolian sediment transport, over the past several decades, has fallen fairly naturally into three overlapping areas: soil erosion; transport of sand by saltation; and the nature and dynamics of eolian bed forms (wind ripples and eolian dunes). (The adjective eolian, meaning produced, eroded, carried, or deposited by the wind, and spelled aeolian in British-style English, comes from the name of a minor Greek god, Aeolos, who was the keeper of the four winds; see the Encyclopedia Mythica or the Wikipedia on the Internet for more information.) This chapter deals with the second of those areas. Loess—deposits of windblown silt that is carried in suspension far from its source, for tens or even hundreds of kilometers—covers a far larger percentage of the Earth’s surface than eolian sand, and it is important for agriculture in many parts of the world, but the topic of loess deposition is beyond the scope of these notes.
- 11.1: Introduction
- Everyone knows that winds on the Earth are commonly strong enough to erode, transport, and deposit sediment. What is perhaps less obvious is that the modes of sediment transport by the wind are greatly different from those of sediment transport by water flows. This great difference lies in the greatly different ratio of sediment density to fluid density, which is almost eight hundred times greater in air than in water.
- 11.2: Saltation I
- The characteristic mode of motion of sand particles in air is saltation: particles are launched from the bed, take arching trajectories of widely varying heights and lengths, and splash down onto the bed at low angles, commonly rebounding and/or putting other particles into motion. Movement by saltation has also been invoked for water transport of particles near the bed (see chapter 10), although the distinctiveness of saltation in water is not nearly as clear as in air.